A summary of breeding seabirds on Skokholm in Total ( in parenthesis)

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2 A summary of breeding seabirds on Skokholm in Total ( in parenthesis) Productivity ( in parenthesis) Fulmar 194 aia (179, 179, 170) 0.57 (0.47, 0.53, 0.34) Manx Shearwater 297 responses in 8000m 2 (269, 241, 263) 0.68 (0.68, 0.63, 0.75) Storm Petrel 90 transect responses (93, 89, 100) 0.58 (0.55, 0.69, -) Puffin 6692 adults (6665, 5070, 4834) 0.73 (0.75, 0.74, 0.73) Razorbill 2242 aol (2382, 2052, 2294) 0.39 (0.21, 0.40, 0.66) Guillemot 3949 aol (3603, 3512, 3466) - (-, -, ) Lesser Black-backed Gull 1397 aia (1486, 1565, 1476) 0.23 (0.15, 0.30, 0.16) Lesser Black-backed x Larus hybrid 1 pair (1, 2, 2) 0 (0, 0, -) Herring Gull 322 nests (289, 300, 263) 0.86 (0.66, 0.70, 0.72) Great Black-backed Gull 93 nests (83, 84, 74) 1.38 (1.66, 0.93, 1.80) Fulmar Fulmarus glacialis Fairly Common Breeder first bred in : 34 trapped Aderyn-drycin y Graig Two birds were on ledges in Hog Bay when staff returned to the Island on the afternoon of 28 th February, however the North Coast cliffs were empty. The following day saw 166 birds logged, 144 of which were on ledges. Colony attendance in March was similarly sporadic with a monthly maximum of 216 on the 8 th followed by a count of just five the following day. Despite lows of between four and 24 on six dates during the month, days when in the majority of cases there was a gale from the westerly quarter, early spring counts higher than in previous years hinted at what was to come. April saw regular departures from the cliffs, with lows of between 36 and 55 noted on six dates but three-figure counts logged on ten dates. Following a 2 nd May total of 102, there was the usual prelaying exodus with 14 days when counts ranged between 12 (on the 9 th, 10 th and 13 th ) and 60. Numbers then increased sharply with 127 logged on the 17 th and 188 the following day when the first egg was noted; the first egg of 2015 was on 21 st May and the first of 2014 was on the 28 th. The three study plots counted annually since 2006 were visited on ten dates between 29 th May and 11 th June. The mean plot count in each year between 2008 and 2014 was routinely three or four birds above the lowest single visit count, however last year saw very consistent totals over the study period and a mean only one bird up on the lowest count (see table below). The number of apparently incubating adults this year was again very similar on each study visit, with a range of just five over the ten dates being the second tightest spread to date. The mean of 27 was the same as logged in 2015 and 2014, the most recorded since the plots were instigated in Although the total was the same, there was again one less pair at Little Bay Point (for a third consecutive year) but one more pair at Middle Rock (also for a third consecutive year). Quite why the Little Bay Point population has declined in each year since 2013, despite the increases seen over the rest of the Island, is unclear. The whole Island totals (apparently incubating adults), mean plot totals, range of totals over the ten study plot visits and the percentage of the Island total made up of study plot birds Island Plots Range (16-25) (16-27) (17-24) (16-22) (16-25) (22-28) (23-29) (26-29) (25-29) Plot % The whole Island count of apparently incubating adults (aia) undertaken between the 2 nd and 5 th June yielded an average of 194aia, an increase of 8.4% on the 179 logged in 2015 and 2014 and the 2 S k o k h o l m S e a b i r d R e p o r t

3 highest total yet recorded on Skokholm. The largest increase was observed along the northeast cliffs where an extra 11aia were between Smiths and Far Bays, whereas totals were static in Hog Bay, Peter s Bay and at the Bluffs. The proportion of the Island total made up of study plot birds thus dropped to 13.9%, the lowest recorded since the plots were begun. Given that the study plot count in previous years has generally followed the same trend as the whole Island count, a static count in a year when the population increased may be a first indication that there is little room in the plots for more pairs. The 2016 whole Island count includes approximately 40 pairs which would be difficult or impossible to see from the Island itself (birds seen from a boat north of North Gully, near Wreck Cove, on the Little Neck and in hidden crevices between Smiths Bay and Little Bay Point). The dip in numbers observed between 2006 and 2012 may perhaps be linked to a lack of boat access. The total number of apparently incubating Fulmar recorded on Skokholm since breeding began in 1967 and the number within the study plots since It is possible that the increase in Fulmar numbers may affect other species; last year saw the departure of a heavily Fulmar-oiled Herring Gull result in the death of its chicks and this year again saw both adult Herring Gulls and their chicks oiled by nesting Fulmars. 3 S k o k h o l m S e a b i r d R e p o r t

4 On 21 st May 54 incubating adults were selected for productivity monitoring (nine at Twinlet, eight at North Gully, 20 around Little Bay Point, four at Rat Bay and 13 at Peter s Bay). Of these two failed at early egg stage, 17 failed at the egg/small chick stage and four failed having definitely produced a chick (with one empty nest seen to contain chick feathers and chicks left alone for one, three and five days prior to going missing); there were none of the failures at large chick stage seen in the previous two years. Thus 31 (57.41%) of the monitored attempts produced a fledgling; a productivity estimate of 0.57 fledglings per pair is 21.3% up on the 0.47 logged in 2015 and 32.6% up on the post 1972 average of Indeed 2016 proved the third best year for Fulmar breeding success on record, not quite matching the 0.59 chicks per pair observed in 2012 or the 0.63 of Nevertheless such high productivity, coupled with a record number of breeding pairs, predicts that 111 Fulmars fledged from Skokholm this year (the first ever three-figure prediction). Poor productivity at Peter s Bay between 2013 and 2015 influenced the overall figure for those years; Peter s Bay productivity in 2013 was 0.06 (compared with an overall figure of 0.34), in 2014 it was 0.33 (compared with 0.53 overall) and in 2015 it was 0.18 (compared with 0.47 overall). This year saw a change of fortunes at Peter s Bay, with seven of 13 monitored attempts fledging; a productivity figure of 0.54 was almost identical to the 2016 average. Fulmar productivity (total number of fledged chicks per monitored pair) for each year that it has been calculated between 1972 and The mean is 0.43 chicks per pair The first fledgling departed its nest ledge on 22 nd August (20 th August in 2015, 23 rd August in 2014 and 25 th August in 2013). All of the study chicks departed over the following 19 days, with 38.7% having fledged by 28 th August, 64.5% by the 30 th and 80.6% by 3 rd September. The last fledgling had departed the Neck by 5 th September and the last study chick fledged on 8 th September (two days earlier than the last of 2015). The number of birds around the cliffs dropped rapidly as the fledglings departed, with a maximum of 88 logged in early September, only 16 birds on the 14 th and the first zero count on the 17 th. Up to seven Fulmar were noted at sea on seven further dates to the end of September and in October there were singles at sea on the 16 th and 17 th and between three and five birds were in Broad Sound on each date from the 26 th to the 30 th ; this was a similar absence to that noted in 2015 and 2014 but contrasts with the higher counts logged in late October 2013 when numbers peaked at 155 on the 30 th. There were records on all but three dates between the 3 rd and 26 th November, with 80 or more logged on ten dates and highs of 161 on the 13 th, 227 on the 14 th, 158 on the 15 th and 160 on the 16 th ; five individuals returned to the breeding ledges at North Gully on the 10 th and birds then took to the ledges on 12 further dates before the departure of staff, with highs of 117 on the 11 th, 110 on the 13 th, 141 on the 14 th and 124 on the 15 th. Manx Shearwater Puffinus puffinus Aderyn Drycin Manaw Very Abundant Breeder a census estimated approximately pairs (46184 in 1998) 4 S k o k h o l m S e a b i r d R e p o r t

5 1447 trapped (including 112 pulli), 625 retrapped, 3 controls : 169,895 trapped, : 5363 trapped, 2065 retrapped, 12 controls One calling from a burrow at dusk on 25 th March was the first to be logged in 2016; this was the latest recorded arrival for six years, five days later than the first of last year. Numbers increased quickly with the first three birds recorded at sea on the 27 th (28 th in 2015), at least 40 around the Lighthouse on the night of the 28 th and 11 fresh corpses found on the 30 th. As in 2015, April seawatching produced some surprisingly small counts, with four-figure totals being logged on only five dates and a high of just 3030 recorded during a southeasterly gale on the 10 th. It proved a remarkably calm May and June, with winds rarely exceeding a moderate breeze and consequently very little diurnal passage off the Lighthouse; the highest spring counts were thus of birds congregating on an evening, with a maximum of noted on 18 th May when birds rafted early in Broad Sound. July counts were higher, with five five-figure counts and a peak of at least logged on a calm 23 rd when up to 600 birds a minute were passing the Lighthouse. The highest counts of the year came in August, with logged during a near gale southwesterly on the 3 rd and noted during similar conditions on the 20 th. A Manx Shearwater study transect was established in It was defined as the track between the Observatory and the Lighthouse and the length of a landing net to either side; ringers were not to deviate from the track. The aim was to see whether, by ringing birds on the surface in this defined area, the retrap data could be interpreted to provide large sample size estimates of adult survival and the recruitment of juveniles to the breeding population. This is very much a project in its infancy and it is too early to draw any conclusions, but here follows a brief summary of the results so far. Of the 875 adult birds ringed along the transect in 2013, 182 (20.8%) were retrapped in 2014 and an additional nine were found predated (with two also predated in the year of ringing). Additionally one was found freshly dead in Brazil in September A further 53 of the 875 were retrapped in 2015 (having not been retrapped in 2014), 32 were retrapped which had been handled in 2014 and five birds were found dead (one of which had been retrapped in 2014). This year there were 22 retrapped which had not been found in 2014 or 2015, 17 were retrapped which had been found in 2014 but not 2015, seven were retrapped which had been found in 2015 but not 2014 and seven were retrapped which have been handled in all three years since ringing. Ten were found dead in 2016, two of which had been retrapped in previous years (one in 2014 and one in 2015). Thus, of the 875 adults ringed in 2013, 278 (31.8%) have been encountered between 2014 and 2016 (and were 5 S k o k h o l m S e a b i r d R e p o r t

6 thus alive in 2014) and 26 birds (3.0%) have been found predated by Great Black-backed Gulls. There were 331 fledglings ringed along the Lighthouse Track in 2013, 11 of which were encountered in 2015 as two year olds. A further six were found this year and three more were handled which had first returned in The number of known age birds along the transect is increasing; along with the 331 fledglings ringed in 2013, there were 374 ringed in 2014, 286 in 2015 and 522 this year. Three areas of study burrows, that is to say natural burrows where a paving slab covers a manmade access point to the nest chamber, were established in 2012 and 2013 with all birds encountered within the burrows ringed. Of 283 breeding adults bearing rings in 2015, 230 were found this year (81.3%). Additionally several birds were encountered which were ringed in 2013 but not found in the study burrows subsequently; thus of 141 breeding adults bearing rings in 2013, 124 (87.9%) were definitely alive in However these figures are not an accurate estimate of adult survival as there was no searching for marked birds in neighbouring, non-study burrows. They do however give a good indication of burrow fidelity and show an interesting correlation with the stability of the colony; in the fragile Lighthouse colony 40 (48.8%) of marked birds were in the same burrow this year as in 2013, whereas in the more stable Crab Bay and Quarry Track colonies 30 (73.2%) and 11 (61.1%) were still present respectively. The fragile nature of the Lighthouse colony, along with the high density of burrowing birds, sees the structure of the breeding tunnels change annually and clearly some lose their suitability as nest sites. Interestingly 33 (53.2%) of the 62 birds which went missing this year had either failed with their breeding attempt in 2015 or had been found without an egg in a burrow in which they had previously bred. Given that this failure rate is significantly higher than the 31.8% observed overall in 2015, it could perhaps be concluded that some of the missing birds have not perished, but rather opted for more suitable nesting sites. The study burrows also facilitate an accurate assessment of breeding success on Skokholm. There were 129 burrows at the Lighthouse occupied by a pair which produced an egg, seven burrows contained an egg along the Quarry Track and 19 pairs produced an egg inland of Crab Bay. There were thus 155 burrows this year from which productivity could be assessed. Of these 19 definitely failed at egg stage and 26 failed at egg or very small chick stage (but neither eggs nor dead chicks were found). Two pairs failed with newly hatched chicks, one of which was found cold and dying alongside an adult which was not incubating it. Finally three pairs lost relatively large and healthy chicks (wings at 90mm, 98mm and 128mm), which were probably predated. For a chick to be 6 S k o k h o l m S e a b i r d R e p o r t

7 assumed to be of fledging size it was required to reach a wing length in excess of 200mm (although not necessarily ready to fledge, we have shown that chicks larger than this size may swap to a different burrow and therefore go undetected). There were 105 chicks which reached this size in Productivity was thus 0.68 fledging sized chicks per breeding pair (67.74% of pairs produced a fledging sized chick). This is a 0.7% drop on the almost identical 2015 figure of 68.24% (which gives the same productivity value of 0.68 fledglings per pair). It should be noted that this is the number of chicks which attained fledging size and does not reflect the number of fledglings which are lost to Great Black-backed Gull (and to a lesser extent corvid) predation as they exercise their flight muscles and make their first flights (see below). Having said that, only one of the 85 fledglings ringed in the Lighthouse study plot was found predated. In 1999 nine study areas, each a circle of 1000 square metres, were established to allow a reasonable subset of the Skokholm Manx Shearwater population to be monitored from year to year. Two of these plots were discontinued, one in 2006 and one in 2007, as the survey work was disturbing the Lesser Black-backed Gull colonies. New plots were established in 2006 and 2015 to maintain a good sample area, however only seven plots have been sampled for a full 17 years. On each annual visit the number of burrows within the area is counted, along with the number of burrows from which a response is elicited when the call of a male bird is played down them. The standard correction factor (1.98) is then used to estimate the population within the area (see the 2013 and 2014 Seabird Reports for checking of the correction factor). The total number of burrows, responses and the corrected population estimate for the 7000 square meters sampled annually since Responses Population Burrows The crash from 2007 numbers was previously attributed to the collapse of many burrows in the more fragile areas of Skokholm, particularly near the Lighthouse which was at one time the densest area of breeding Manx Shearwaters on the Planet (Smith et al., 2001). Although this may certainly have played a role, it seems unlikely that it would be a major factor as there are considerably more burrows than pairs and the number of burrows appears to fluctuate independently of the number of tape playback responses. The eighth sample plot, begun in 2006, shows nicely the apparent lack of connectivity between the number of burrows and the apparent number of breeding pairs (see graph below). This may be attributable to the number of burrows frequently being altered by Rabbits, the weather, in some areas by Puffins and perhaps most markedly in some places, the digging of nonbreeding Manx Shearwaters, particularly later in the season. 7 S k o k h o l m S e a b i r d R e p o r t

8 The total number of burrows, responses and the corrected population estimate for the 1000 square meter plot sampled annually since Although the number of birds in the 2006 plot (which lies to the south of North Pond) has seemingly declined since its introduction, this year saw a slight increase in responses compared with 2014 and The overall number of responses across 8000 square metres was the highest since This was the result of an increase of between one and eight responses in five of the seven longer-term study areas, with an identical number of responses from the Neck plot and a drop of three only noted at the plot on North Plain. It would appear that the Skokholm breeding population can still be cautiously regarded as stable, although the observed variance in the percentage of birds which respond to the playback on a given day highlights both the degree of error in these numbers and the importance of continued monitoring (see Brown and Eagle, 2013 and 2014). Some supporting evidence for a stable population comes from the adult ringing programme, with an overall return rate this year of 81.27% compared with 77.34% in 2015 and 82.27% in The estimated number of pairs in the 8000 square metres sampled since In the period between 1957 and 1997 the number of dead Manx Shearwaters located on Skokholm was recorded in the daily census log. The corpses were either stored or thrown into the sea to ensure that birds were not counted more than once. The practice was stopped in 1997 as it was felt that the removal of the corpses would be impacting the specialist community of species evolved to exploit this food source. However, with a Great Black-backed Gull population more than twice the size it was when the counting was stopped, the study was begun again in To limit the impact on the scavenging community, the birds were left in situ but their wings were painted with stock marker so that they were not double counted. This year, as in 2015, corpses were marked by neatly slicing the flight feathers of both wings with a pair of scissors. The number of Manx Shearwater corpses found between 1957 and 1983 from Gynn (1984) plus data from 1984 to 1991 and 2014 to The number of Great Black-backed Gull breeding pairs is also included for each year Corpses GBBGU Responses Population Burrows 8 S k o k h o l m S e a b i r d R e p o r t

9 25/3-31/3 1/4-7/4 8/4-14/4 15/4-21/4 22/4-28/4 29/4-5/5 6/5-12/5 13/5-19/5 20/5-26/5 27/5-2/6 3/6-9/6 10/6-16/6 17/6-23/6 24/6-30/6 1/7-7/7 8/7-14/7 15/7-21/7 22/7-28/7 29/7-4/8 5/8-11/8 12/8-18/8 19/8-25/8 26/8-1/9 2/9-8/9 9/9-15/9 16/9-22/9 23/9-29/9 30/9-6/10 7/10-13/10 14/10-20/10 21/10-27/10 28/10-3/ Corpses GBBGU Corpses GBBGU Corpses GBBGU As might be expected with a larger Great Black-backed Gull breeding population, the number of corpses marked over the last three years has been the most ever. However the average number of corpses per pair has been lower than in all years except 1959, 1970 and One possible explanation for this reduction in kills per pair is that the breeding gulls were routinely disturbed between 1949 and 1985 which, although reducing the number of breeding pairs, probably inflated the non-breeding flock which would still be taking shearwaters The number of Manx Shearwater corpses found during each week from 25 th March until 3 rd November Puffinosis Fledglings Chicks Adults There was a reduction in the number of dead Manx Shearwaters located this season, despite the increase observed in the number of breeding Great Black-backed Gulls. This was primarily due to a significant decline in the number of adult birds located; in 2014 there were 2931 dead adults marked, in 2015 there were 2702 and in 2016 there were only Up until 30 th June numbers were relatively consistent with previous years (just 46 down on 2014), but between 1 st July and the end of the season there were 586 fewer corpses than in 2014 and 193 fewer than in It is tempting to think that a major factor influencing the number of shearwaters being taken each year is the size of the Rabbit population (Rabbits being the other main prey item on Skokholm). The data from the last three years lends some support to this theory, with the North Plain Rabbit population being considerably lower in 2014 (when adult mortality was at its highest). In contrast to adult mortality, the number of young shearwaters found predated this year was the highest ever; there were 1288 young birds found predated in 2014, 1324 in 2015 and 1398 this season. Intriguingly Rabbit numbers declined during the middle of the 2016 season, with totals beginning at a level similar to that seen in 2015 before declining to a level similar to the autumn low of 2014 (see graph below); perhaps the decline in Rabbit numbers led to the increase in autumn shearwater mortality. 9 S k o k h o l m S e a b i r d R e p o r t

10 04-Jul 07-Jul 10-Jul 13-Jul 16-Jul 19-Jul 22-Jul 25-Jul 28-Jul 31-Jul 03-Aug 06-Aug 09-Aug 12-Aug 15-Aug 18-Aug 21-Aug 24-Aug 27-Aug 30-Aug 02-Sep Of course young shearwaters, which provide a considerably larger meal than an adult and which are less experienced on land, may prove to be the preferred prey item for the gulls regardless of the number of Rabbits. The Skokholm Rabbit population has been considerably lower than in previous years during the three years of this carcass marking study; for example in 2013 the highest plot count was 463 on 22 nd May compared with a maximum count of 150 during the last three years. A return to 2013 Rabbit numbers would provide ideal conditions for monitoring their impact on shearwater predation. The total number of Manx Shearwater carcasses found each week and the number of Rabbits counted in the North Plain census plot during the same period [Grab your 2014 Total 2015 Total 2016 Total 2014 Rabbits 2015 Rabbits 2016 Rabbits The growth of 12 Manx Shearwater chicks was monitored in the Lighthouse Study Plot (see graph below). There were no synchronised drops in weight (as was observed during bad weather in 2014) and four individuals reached weights in excess of 600g (with one attaining 684g); the heaviest of 24 chicks monitored in 2014 and 2015 were 595g, 594g and 592g The weights (g) of 12 Manx Shearwater chicks in the Lighthouse Plot Study Burrows. The first fledglings were seen above ground on the night of 23 rd August, two days later than in 2015, two days earlier than in 2014 and on the same date as in The first fledgling showing symptoms 10 S k o k h o l m S e a b i r d R e p o r t LH11 LH16 LH25 LH75 LH81 LH66 LH52 LH104 LH109 LH137 LH91A LH80

11 of puffinosis was encountered during the day on 29 th August, two days later than last year. There was a small drop in the number of dead shearwaters showing signs of the disease this year (85 compared with 97 in 2015); it should be noted however that, unlike predated birds which are taken to open areas, puffinosised birds may die deep in the Bracken and thus go undetected. Puffinosis is a mysterious affliction which, possibly due to the actions of a virus which leads to bacterial infection, sees the development of blistered feet, conjunctivitis and problems with limb control; it is often fatal. In an attempt to achieve a better understanding of how puffinosised birds are distributed across Skokholm during the course of the autumn, a transect established in 2015 was walked by Island staff over eight nights during September (see the 2015 report for details of the route). The position of each encountered fledgling was recorded using a GPS unit before it was inspected for signs of puffinosis. The 2016 puffinosis survey. Manx Shearwater fledgling density is shown in green, with the darker areas around the Well and Knoll Wall holding more birds. Each puffinosised bird encountered over the eight visits is marked by a yellow dot. The number of Manx Shearwater fledglings located along the transect is likely to be different between years, not just because of fluctuations in productivity, but perhaps more critically due to differences in the weather and the moon cycle. In total over the eight visits there were 234 fewer fledglings encountered this season (a drop of 24.5%). The overall proportion of birds showing signs of puffinosis was also well down, with 13.47% of birds showing signs this year compared with 29.14% in Interestingly the proportion of birds showing signs of puffinosis did not increase during the course of September as it did in 2015; this increase was considered to be not just a reflection of the emergence period of infected birds, but also due to their inability to fledge causing a prolonged presence in the study area. As in 2015, puffinosised birds were primarily distributed in the wetter areas of Skokholm, away from more exposed aspects which also typically lack Bracken. 11 S k o k h o l m S e a b i r d R e p o r t

12 The number of fledgling Manx Shearwater encountered along the transect in 2016 and 2015, the number which showed signs of puffinosis and the proportion of encountered birds made up of those showing signs nd -3 rd 5 th -6 th 8 th -9 th 11 th -12 th 14 th -15 th 17 th -18 th 20 th -21 st 23 rd -24 th Birds Puffinosised % Puffinosised st -2 nd 4 th -5 th 7 th -8 th 10 th -11 th 13 th -14 th 16 th -17 th 19 th -20 th 21 st -22 nd Birds Puffinosised % Puffinosised The last two adult birds to be encountered along the study transect were retrapped on 26 th September, three weeks later than the last of September seawatch counts peaked at 732 individuals on the 3 rd, with seven further three figure counts logged during the month. However there was only one bird seen at sea in 90 minutes on the 10 th and there were no at sea records on the 17 th (one day later than the first zero count day of 2015 and 2014). Birds were noted at sea on 11 subsequent dates in September and fledglings were still encountered each night. In October there were four at sea on the 17 th and fledglings were recorded each night (or freshly predated the following morning) on all but six dates to the 23 rd. There were five records at sea during November, with singles in Broad Sound or off the Lighthouse on the 5 th, 12 th and 17 th, five shearing their way west together off the Lighthouse on the evening of the 22 nd and two in Broad Sound the following day which were the last of the year (five days later than the last of 2015 and eight days later than in 2014). The only later Skokholm records are singles logged on the 24 th and 26 th November Ringing recovery EB52831 Originally ringed as a chick, SKOMER ISLAND, PEMBROKESHIRE 30 th July 2013 Recovered SOUTH HAVEN, SKOKHOLM 7 th August 2016 Finding condition At colony but not necessarily breeding Distance travelled 4km at 163 degrees (SSE) Days since ringed 1104 A three year old bird exploring a colony away from its natal island. Ringing recovery EF98315 Originally ringed as a chick, LUNDY ISLAND, DEVON 7 th September 2007 Recovered MANX SHEARWATER TRANSECT, SKOKHOLM 18 th August 2016 Finding condition At colony but not necessarily breeding Distance travelled 74km at 325 degrees (NW) Days since ringed 3268 Rats had officially been eradicated on Lundy by 2006 (although the last recorded activity was in February 2004). By 2013 the shearwater population there had increased by over 3000 pairs. As with the preceding recovery, this nine year old seemingly investigated a colony away from its natal site; given the age of this bird it seems likely that it then selected a nest burrow on Skokholm. Ringing recovery EX28101 Originally ringed as a juvenile, FRESHWATER WEST, PEMBROKESHIRE 9 th September 2011 Recovered MANX SHEARWATER TRANSECT, SKOKHOLM 5 th August 2016 Finding condition At colony but not necessarily breeding Distance travelled 16km at 291 degrees (WNW) Days since ringed 1792 Further evidence that birds which inadvertently reach the mainland after fledging can go on to survive, as long as they make it back out to sea. 12 S k o k h o l m S e a b i r d R e p o r t

13 Ringing recovery EY86519 Originally ringed as a breeding adult, LIGHTHOUSE STUDY PLOT, SKOKHOLM 31 st May 2014 Recovered OXWICH POINT, SWANSEA 30 th July 2016 Finding condition Dead on strand line Distance travelled 79km at 103 degrees (ESE) Days since ringed 791 This bird bred in the same nest chamber in 2014, 2015 and 2016, however the attempt failed in all three years (twice at egg stage, once with a small chick). The reason for failure in 2016 is now clear. Ringing recovery EZ16472 Originally ringed as an adult, MANX SHEARWATER TRANSECT, SKOKHOLM 22 nd July 2015 Recovered OLIVENÇA, ILHÉUS, BRAZIL 17 th October 2016 Finding condition Dead on beach Distance travelled 8106km at 205 degrees (SSW) Days since ringed 453 Ringing recovery EZ16723 Originally ringed as an adult, SKOKHOLM 15 th August 2015 Recovered near SAO MATEUS, ESPIRITO SANTO, BRAZIL 24 th September 2016 Finding condition Dead on beach, eaten by scavengers Distance travelled 8558km at 204 degrees (SSW) Days since ringed 406 Ringing recovery EZ17838 Originally ringed as an adult, MANX SHEARWATER TRANSECT, SKOKHOLM 11 th August 2016 Recovered INGLESES, FLORIANÓPOLIS, BRAZIL 28 th September 2016 Finding condition Dead on beach Distance travelled 9765km at 206 degrees (SSW) Days since ringed 48 There was a single recovery from Brazil in the winter of 2014/15, two from the winter of 2015/16 and already three from 2016/17, totals which probably reflect the increase in the number of Skokholm ringed birds. The last of these three recoveries was part of a mass stranding. Ringing recovery EZ16946 Originally ringed as a fledgling, MANX SHEARWATER TRANSECT, SKOKHOLM 3 rd September 2015 Recovered TEXACO OIL REFINERY, ANGLE, PEMBROKESHIRE 2 nd November 2015 Finding condition Dead at a Peregrine roost Distance travelled 19km at 96 degrees (E) Days since ringed 60 Storm Petrel Hydrobates pelagicus Pedryn Drycin Abundant to Very Abundant Breeder a 2016 whole Island survey predicted 1910 occupied sites 705 trapped (including 6 pulli), 38 retrapped, 25 controls : 18,526 trapped, : 1838 trapped, 136 retrapped, 72 controls Despite the sizable breeding population on Skokholm, Storm Petrels again proved a rare sight at sea. The only records were of eight on 20 th August (seven in a two hour morning seawatch and one in the evening), two west off the Lighthouse on the evening of 21 st August and a single there on 3 rd September; all other observations came at night, with the exception of a small number of incubating adults visible in shallow crevices or in nest boxes. A minimum of seven birds watched at the Quarry on 19 th April was the first record of the year, three days earlier than the first of 2015 and five days 13 S k o k h o l m S e a b i r d R e p o r t

14 earlier than in The first diurnal record was of a vocal bird in the Quarry on 8 th May. Nights in May saw small numbers observed at various locations around the Island and there were minimum counts from the Quarry of 80 on the 21 st and 90 on the 25 th. The Quarry in 2003 and The massive rocks labelled A, B and C, along with a substantial number of surrounding boulders, slipped between the mornings of 19 th and 21 st June Transect two, which ended at a cave between B and C, was in the most part destroyed. A B C 14 S k o k h o l m S e a b i r d R e p o r t

15 Four transects established at the Quarry in 2010, along with further plots in North Haven Gully and along two of the walls which radiate from the Farm, provide much more reliable population monitoring than nocturnal count data. Between 91 and 129 responses were elicited at these sites in the years 2010 to 2015, however this season saw a substantial rock slide significantly reduce the area which could be directly compared to these years (see photographs above). Quarry transect two, which has held between eight and 22 responding birds, was almost entirely destroyed (presumably with the loss of the majority of petrels incubating at the time). Additionally Quarry transect one was showered with loose rubble and undercut on its southern edge. It would seem from the records that this was by far the largest such event for over 30 years. Transect two was not accessed at all for the 2016 survey and transect one was only accessed on four occasions, rather than the usual ten, owing to concerns over its stability. The rock slide was not seemingly caused by any extremes of weather, with winds during June not exceeding a fresh breeze and with no intense rainfall events; however 15 dry days had been followed by an 11 day period in which rain fell, albeit in unremarkable quantities, on nine dates, conditions perhaps responsible for a change in the soil which supported some of the rocks. It is hoped that the winter will be sufficient to stabilise transects one and two and allow the sites to be used again during the 2017 season; if this area remains unstable, alternative sites will be incorporated into the project to maintain a reasonable sample size. For a third consecutive year we welcomed a long-term Storm Petrel volunteer who made ten visits to the study areas between 15 th June and 8 th July. A recording of male song was played into every crevice encountered along the transects, both numbered (and therefore used previously) and unmarked, with each crevice from which a response was elicited being recorded and marked if new. It was first noted in 2013 how some study burrows had deviated from the two metre wide transects and in 2014 the data collected since 2010 was reassessed to bring it back in line with the original protocol. As was the case in 2014 and 2015, the playback census this year was focused on the area of the transects delineated by marked burrows, although the results were then divided into those which fell within the true transect and those which fell just outside (see table below). The total number of apparently occupied crevices (located over ten visits) responding to a recording of male song at each of the seven study sites. Numbers in parenthesis are the totals from the 2m wide Quarry transects (as stipulated in the project guidelines) as opposed to the more wayward crevices included since the project s inception. The mean is that from Year North Pond Wall Little Bay Wall North Haven Gully Quarry transect 1 Quarry transect 2 Quarry transect 3 Quarry transect 4 Quarry total Total (5) 15 (12) 11 (8) 32 (17) 66 (42) 97 (73) (5) 13 (8) 10 (7) 25 (14) 59 (34) 91 (66) (5) 8 (4) 10 (5) 33 (17) 63 (31) 98 (66) (4) 15 (8) 10 (7) 46 (27) 85 (46) 129 (90) (5) 18 (9) 18 (12) 37 (22) 87 (48) 121 (82) (5) 22 (9) 12 (7) 40 (25) 87 (44) 128 (89) * (2)* ** ** 11 (8) 41 (26) 61 (36) 99 (74) Mean * Transect 1 was only visited on four occasions due to safety concerns. ** Transect 2 was not visited in 2016 due to a rock fall. Owing to the loss of transect two and a reduced number of visits to transect one, the number of active crevices located this year was the lowest since However, given the reduced study area, it was encouraging that the total still exceeded that logged between 2010 and If transects one and two are removed from the equation, the 2016 season proved the third best on record, with totals extremely similar to the previous year; in areas where a direct comparison can be made, there 15 S k o k h o l m S e a b i r d R e p o r t

16 were only three fewer responses than in 2015 (and only one less response if the study area is confined to the two metre wide Quarry transects). The number of responses elicited at each site visited ten times were very close to the means. The largest differences were at Little Bay Wall, where there appears to have been a genuine increase since , and at Quarry transect four which has seen a similar increase over the same period. The number of responses at North Haven Gully was the same as in 2015, with the breeding season population at this site stable after the significant scouring event of winter which removed 21 of the crevices occupied between 2010 and 2013 (and 16 of those occupied in 2013). It seems likely that the Skokholm study population away from the Quarry rock fall area can still be regarded as stable, a conclusion which is probably applicable to the Island population as a whole (assuming of course that substantial rock fall events such as that witnessed this year remain rare). This is positive news following what may have been a significant population decline between 1996 and 2010 (Sutcliffe and Vaughan, 2011). The total number of responses elicited with Quarry transects one and two omitted. Numbers in parenthesis are the totals which include only the 2m wide Quarry transects. The mean is that from Mean 74 (56) 67 (53) 78 (57) 100 (78) 89 (68) 93 (73) 90 (72) 83.5 (64.2) Clearly some Storm Petrel nest crevices can be short lived (nearly a third of those found over the course of this study have only been occupied for one year), but there also seems to be evidence that the birds react to the changing landscape and maintain a stable population; this of course assumes that further nest sites open up as others are lost. Stable sites are also in existence; over a quarter of the active crevices located during this seven year study have shown signs of occupancy in five or more years and over 6% of crevices have contained a calling bird in every year. The number of crevices which have at some point been occupied over the seven year study (a total of 247), subdivided to show how many years the crevices have been apparently occupied for and the percentage of crevices occupied for a particular number of years. Quarry Transects The Walls North Haven Gully Total % of total 1 year of apparent occupancy years of apparent occupancy years of apparent occupancy years of apparent occupancy years of apparent occupancy years of apparent occupancy years of apparent occupancy Total In areas of rock fall (in the Quarry and North Haven Gully), the percentage of known active crevices which responded to a recording of male song during any single visit was down on the previous two years. At the walls a higher proportion of birds responded than in 2015 and On average over the last three years, a significantly higher proportion of birds have responded at the walls than in the rock fall on each visit. It is tempting to think that this site specific variation may be due to the distance that the birds are from the playback device, however other factors such as the density of breeding or non-breeding birds (which will affect how often they are usually exposed to real Storm Petrel song), may also be at play. If more non-breeders (birds which may leave a crevice unattended or occupy multiple crevices during the study period), are present in areas of high breeder density such as the Quarry, then the overall response rate would be lower at this site. To account for these differences, it may be best to treat the two habitat types separately when calculating a correction 16 S k o k h o l m S e a b i r d R e p o r t

17 factor which predicts the number of birds present based on just a single visit (see table below). During the 2016 study period a mean correction factor of 3.61 would most accurately predict the number of birds in any area (a figure really quite similar to the 3.33 of 2015 and the 3.56 of 2014). However, of the ten visits made in 2016 to sites which contained 90 active crevices, the lowest number of responses from a single visit was ten and the highest 41, meaning that the correction factor could vary from 9.00 to 2.20 depending on the visit. There was similar variance around the habitat specific response rates; in the rock fall areas there were 69 active crevices and a mean of 16.5 responses per visit, although on one occasion only five birds responded and on another 28 giving a correction factor which varied between and 2.46 (with a mean of 4.18); at the Walls, where there were 21 active crevices, a mean of 8.4 birds per visit responded, although on one occasion it was five and on another 13 (the correction factor thus varied between 4.20 and 1.62 with a mean of 2.50). The percentage of known active crevices which responded to male song during any single visit, averaged across all visits (the resulting correction factor is given in parenthesis). Year The Walls North Haven Quarry Rock fall Average (2.76) 40.0 (2.50) 26.2 (3.82) 26.4 (3.79) 28.1 (3.56) (3.48) 37.4 (2.68) 28.9 (3.46) 30.4 (3.29) 30.1 (3.33) (2.50) 25.9 (3.86) 23.3 (4.30) 23.9 (4.18) 27.7 (3.61) Despite the variation observed in response rates, the production of a correction factor is the best way to predict the number of birds present in a large area when ten visits are not logistically feasible. With this in mind, a whole Island Storm Petrel census was undertaken in 2016, with funding from Natural Resources Wales providing six staff and equipment (see Wood et al., 2017). A single visit was made to every area of Skokholm containing suitable nesting habitat (with the exception of a small number of cliff faces and the Quarry rock fall area which were either extrapolated for using areas of similar habitat or monitored using an infrared viewer as the birds returned at night). The majority of individuals which responded to the playback survey were hidden in complex crevices, however a small number of birds were found to be using surprisingly open sites; the incubating bird pictured below was in an open, angled crevice, however the resulting chick was always found to be dry following rainfall and it went on to fledge. The whole Island census period was the same as that used for the transect survey, with the vast majority of work undertaken between 15 th June and 8 th July. The exception was a small number of sites which are also used by breeding auks or raptors; at the Bluffs and along the coast of Mad Bay the survey period was extended to 13 th July so as to avoid disturbance to auks and Peregrines and at 17 S k o k h o l m S e a b i r d R e p o r t

18 Wreck Cove the survey was conducted on 21 st July when the Buzzard fledgling had left the site. The earlier study period is preferable as it in the most part avoids the influx of non-breeding birds which occurs from July onwards, birds which occupy crevices during the day and respond to playback (leading to an overestimation of the breeding population). The most complex rock fall area on Skokholm, the Quarry, was surveyed using a recent aerial photograph (captured using a University of Gloucestershire drone), to map out discreet areas using recognisable rocks to delineate the boundaries; each of these intuitive polygons could be surveyed separately, without the risk of missing areas or double counting as may occur if such large expanses of complex habitat are visited in one go. The remaining areas of rock fall on Skokholm proved sufficiently discreet for each to be surveyed separately, with completed areas recorded on a map of the Island. The intuitive polygons used to survey the Quarry in The use of a recent photograph meant that all of the stones used as marker points were present on the ground. Although it would perhaps prove difficult to survey exactly the same areas in future years (owing to the movement of marker stones), a similar technique should be used. The Danger Area affected by the June rock slide was not accessed in This is very much a three dimensional habitat, with several of the polygons containing caves into which the survey workers could crawl (from Wood et al., 2017). The Quarry total is an amalgamation of data from transects three and four, intuitive polygons and the extrapolated danger zone. The Quarry transects were visited ten times and contained a total of 18 S k o k h o l m S e a b i r d R e p o r t

19 52 apparently occupied sites (AOS). The danger area was calculated as being 1.2 times the area of transects three and four, giving a predicted total of 62.4 sites (although previous survey work had suggested that this area contained a particularly high density of birds). There were 139 responses elicited from the polygons. It was important to get a separate total for the Quarry as a whole as this area has traditionally been the focus of the majority of survey work on Skokholm (see below); several previous whole Island estimates have been extrapolated from the Quarry total. Across the whole of Skokholm there were 350 AOS discovered in areas of rock fall (including the Quarry polygons) and 27 AOS in the walls. The mean correction factor of 3.61 ( ), predicts a total of ( ) AOS in rock fall and ( ) in the walls. The habitat specific correction factors predict a rock fall total of ( ) AOS and a walls total of ( ) AOS. Much of Skokholm is burrowed due to Rabbit, Puffin and Manx Shearwater activity. Such burrows, particularly those made by Rabbits, are used by a large proportion of the French breeding Storm Petrel population and they have been reported from earthen sites on Skokholm too (although this is currently believed to be a rare occurrence). In an effort to assess burrow use on Skokholm, an area north of the Table measuring 1000m 2 was surveyed, with every burrow having Storm Petrel song played down it. This location was considered a good place to search for burrow nesters as its close proximity to the Quarry would increase the likelihood that the burrows had been encountered by prospecting petrels. No responses were elicited. It may still prove to be the case that some Storm Petrels use burrows on Skokholm, but in the absence of any recent records of such activity this habitat type was subsequently excluded from the whole Island survey. A small number of inaccessible areas not covered by the playback census were found to hold Storm Petrels, namely rock fall at the bottom of Oven Point, Nell s Bay, Fossil Bay, Steep Bay and Twinlet and the cliff faces at the Quarry and Hump Bay. These areas were monitored using an infrared 19 S k o k h o l m S e a b i r d R e p o r t

20 viewer and the number of birds watched entering crevices was compared to that at a similar site which could be surveyed using the playback technique (thus allowing a correction factor to be calculated for the inaccessible sites). There were nine birds recorded at North Haven (where 17 responses were elicited over ten visits using playback). The resulting correction factor of 1.89 predicts that there were AOS at the inaccessible sites (Wood et al., 2017). Combining all of the data collected during the 2016 whole Island census, a total of 1597 AOS is predicted using the mean correction factor and 1766 AOS are predicted using the habitat specific correction factor. However there is a third, preferred technique. The data collected this season has been further analysed as, after ten visits to the playback areas, a small number of new sites were still being found. The correction factors were thus increased to include birds predicted to have been present but which did not respond during the ten visit study period (using a method which predicts the eventual asymptote in the cumulative number of occupied sites see Wood et al., 2017). This technique predicted a total of 1910 sites, a figure which is considered the most accurate Skokholm total to date (Wood et al., 2017). One issue with such a technique is that the number of breeding birds responding to the playback may have already reached an asymptote, the active burrows detected late in the survey being non-breeders. There is an obvious need to know what responding birds are actually doing; it is unclear how the 1910 AOS predicted this year actually corresponds to the number of breeding pairs on Skokholm. Given that previous attempts to use an endoscope in natural sites have failed, one way to improve our knowledge is to encourage petrels to occupy accessible artificial nest sites. With this in mind a study wall containing 119 nest holes was created during the 2016 season. Any uptake will be reported in future Skokholm Seabird Reports. 20 S k o k h o l m S e a b i r d R e p o r t

21 Previous studies have concentrated on securing an accurate estimate for the Quarry (and on occasion a subset of other areas) and have used this density to predict a total for the rest of the Island based on an estimate of available habitat. Even in these cases the Quarry totals were extrapolated, typically from surveys of 250m 2 (17.5% of an estimated Quarry area of 1425m 2 ). Additionally, previous whole Island estimates have been based on differing evaluations of available habitat, with the ratio of Quarry to suitable habitat across the whole Island being predicted to be in the region of 1.92 to 3.30 (the 5.31 used on Thompson s 2003 survey by Sutcliffe (2010) appears erroneous). The different results from previous surveys are thus in part due to the different techniques used. Previous whole Island censuses predicted 4200 sites in 1994 (Betts, 1994), in 1995 (Vaughan & Gibbons, 1996), in 2001 (Vaughan, 2001), in 2003 (Thompson, 2003 and Sutcliffe, 2010) and 1920 in 2010 (Sutcliffe, 2010). Although the downwards trend between 1994 and 2016 is perhaps in part the result of differing survey techniques, the significantly higher Quarry totals predicted in the mid-1990s suggest that the Skokholm Storm Petrel population has undergone a genuine decline before subsequently stabilising in the 21 st Century; the Quarry has previously been estimated at 1550 pairs, more than twice the number believed to be there now. Nevertheless, the 2016 survey suggests that Skokholm is still the fourth largest Storm Petrel colony in Britain and the largest in Wales. In 2013 a thermal imaging camera recorded a Short-eared Owl hunting Storm Petrels in the Quarry, an event which is perhaps more regular than previously realised. The remains of six petrels were found that year, 16 in 2014 and 18 in 2015, the vast majority of which were believed to be owl victims. This season there were 51 corpses located between 30 th April and 4 th September, the majority of birds again thought to have fallen prey to Short-eared Owls (due to the presence of feathers or pellets near the bodies). Although it is tempting to link this 2016 rise to increased vigilance in coastal areas during the whole Island census, the majority of corpses were found near the path network or in areas of the Quarry visited regularly for transect monitoring. What is perhaps thus a genuine increase in the number of predated Storm Petrels may be linked to increased Shorteared Owl activity this season; whereas in recent years it was believed that owls were commuting from Skomer to feed, this season there were up to two present in May (including a male which occasionally gave its advertising call) and very regular sightings during June and July. Additionally there was an increase in the number of owls encountered in the Quarry at night, with guided walks on the 21 st and 28 th May and on the 6 th, 13 th and 18 th July encountering hunting Short-eared Owls. The owls did not breed successfully on Skokholm this year, indeed there is no record of a breeding attempt in over 80 years of observations, but it seems likely that they were at least resident for a time this summer. Two of the Storm Petrel carcasses were in Peregrine nests (one in each); there were no records of Peregrines taking petrels during the previous three years. There were 19 sites discovered this season where an incubating bird was evident early enough in the nesting period to allow a productivity estimate to be made (20 sites in 2015 and 13 in 2014); although some early egg stage failures may have been missed, the study is biased towards birds in shallow crevices or boxes and the sample size is far from great, these visible birds provide a rare opportunity to estimate productivity on Skokholm. Seven of these visible birds, including six in boxes, were this season used for a British Trust for Ornithology tracking project; four birds were fitted with geolocators and three birds were handled for a similar period but not fitted with trackers. The remaining 12 study burrows were thus used for producing a 2016 productivity figure which could be compared with the previous two seasons. Of these four failed at egg stage, one failed with a chick which was at least 30 days old and seven fledged young; productivity was thus calculated at 0.58 fledglings per pair, a figure very similar to the 0.55 observed in 2015 but down on the 0.69 recorded in All four tracker birds failed with their breeding attempts; although one healthy chick was found flooded from its nest chamber, in at least one other case it was felt that a chick died because it was not being fed regularly (having reached 32.3g it dropped to 21.8g, increased to 30.3g 21 S k o k h o l m S e a b i r d R e p o r t

22 30-Jul 01-Aug 03-Aug 05-Aug 07-Aug 09-Aug 11-Aug 13-Aug 15-Aug 17-Aug 19-Aug 21-Aug 23-Aug 25-Aug 27-Aug 29-Aug 31-Aug 02-Sep 04-Sep 06-Sep 08-Sep 10-Sep 12-Sep 14-Sep 16-Sep Wing length (mm) Weight (g) and then gradually lost weight, this compared to the other study chicks which all reached at least 42.7g). Of the three birds handled in the same way as the tracker birds, one failed at chick stage (although it was believed that the chick may have been predated as feathers were found around the entrance to the box) whilst two fledged young (0.67 fledglings per pair) Monitoring the development of three Storm Petrel chicks Bluffs 10 wing Quarry box A wing 40 Quarry 18 wing Bluffs 10 weight 20 Quarry box A weight Quarry 18 weight The first two hatched eggshells were not found until 17 th July this year, 15 days later than the first of 2015; given that the majority of eggshell remains in the crevice, it would seem likely that these dates are not a good indication of when chicks first hatch. The first study burrow chick left alone during the day was found on 24 th July. The growth of three chicks was monitored from when they were 22 S k o k h o l m S e a b i r d R e p o r t

23 known to be unattended during the day (see graph above). These chicks were from different burrows to those used in the three previous seasons as those regular sites were used for the tracking project. The three chicks monitored this year reached peak weights of 48.0g, 48.8g and 46.5g; the heaviest monitored chick in either 2014 or 2015 reached only 46.5g. One of the geolocator project control nests contained a chick which reached a staggering 50.1g on 30 th August. As in the previous two years some chicks were found to move from their natal cavity although, unlike last year when some small chicks moved during bad weather, only young close to fledging were found to relocate this year. All nine of the study burrows which contained fledglings were vacated between the 16 th and 22 nd September. Adult Storm Petrels were mist netted on eight nights this year, three fewer than in The largest catch was the 247 trapped on the night of 22 nd July. Of all the birds handled this year, 6.8% were already wearing a ring (12.3% in 2015, 7.5% in 2014), there were two retraps from 2014, 20 retraps from 2015 and 22 (3.03%) of handled birds had been ringed elsewhere (3.45% in 2015). Along with generating some fantastic data, these nights also proved very popular with guests to the Island. Unless stated otherwise, all of the following recoveries were of birds deliberately mist netted. Additional to the birds listed below, we received news of eight birds ringed at Wooltack Point (4km to the NNE) retrapped on Skokholm (seven after between 22 and 28 days and one after 1112 days), six birds ringed on Skokholm and retrapped on Wooltack (after 315, 324, 325, 332, 689 and 705 days respectively), four birds ringed on Skomer (4km to the NNW) retrapped on Skokholm (after between one and four days) and six birds ringed on Skokholm and retrapped on Skomer (after three, 25, 370, 716, 741 and 756 days). Two of the birds retrapped on Skomer had also been retrapped there the previous year (without tape luring) and are perhaps thus breeding there. Ringing recovery Originally ringed as an adult, ST JUSTINIAN, ST DAVID S, PEMBROKESHIRE 30 th July 2016 Recovered SOUTH HAVEN, SKOKHOLM 14 th August 2016 Distance travelled 19km at 170 degrees (S) Days since ringed 15 Storm Petrel made the reverse journey; having been ringed on Skokholm on 26 th July 2016, it was mist netted at St Justinian four days later. Ringing recovery Originally ringed as an adult, BARDSEY ISLAND, GWYNEDD 21 st July 2016 Recovered SOUTH HAVEN, SKOKHOLM 23 rd July 2016 Distance travelled 122km at 196 degrees (SSW) Days since ringed 2 Ringing recovery Originally ringed as an adult, BARDSEY ISLAND, GWYNEDD 12 th August 2016 Recovered SOUTH HAVEN, SKOKHOLM 14 th August 2016 Distance travelled 122km at 196 degrees (SSW) Days since ringed 2 Ringing recovery Originally ringed as an adult, GRASSHOLM, PEMBROKESHIRE 5 th August 2016 Recovered SOUTH HAVEN, SKOKHOLM 6 th August 2016 Distance travelled 15km at 106 degrees (ESE) Days since ringed 1 Three birds ringed on Skokholm in July 2016 were subsequently mist netted on Grassholm, namely there 13 days later, there ten days later and also there ten days later. 23 S k o k h o l m S e a b i r d R e p o r t

24 Ringing recovery Originally ringed as an adult, HARTLAND POINT, DEVON 7 th July 2016 Recovered SOUTH HAVEN, SKOKHOLM 10 th August 2016 Distance travelled 95km at 326 degrees (NNW) Days since ringed 34 Storm Petrel ringing recoveries (over 10km) received since the Bird Observatory was reaccredited. Google Imagery 2014 TerraMetrics Ringing recovery Originally ringed as an adult, HARTLAND POINT, DEVON 8 th July 2016 Recovered SOUTH HAVEN, SKOKHOLM 26 th July 2016 Distance travelled 95km at 326 degrees (NNW) Days since ringed 18 Ringing recovery Originally ringed as an adult, MWNT, CEREDIGION 24 th July 2015 Recovered SOUTH HAVEN, SKOKHOLM 6 th August 2016 Distance travelled 65km at 223 degrees (SW) Days since ringed 379 Ringing recovery Originally ringed as an adult, THE LIZARD, CORNWALL 17 th June 2015 Recovered SOUTH HAVEN, SKOKHOLM 6 th August S k o k h o l m S e a b i r d R e p o r t

25 Distance travelled 193km at 359 degrees (N) Days since ringed 416 Ringing recovery Originally ringed as an adult, SOUTH HAVEN, SKOKHOLM 24 th July 2014 Recovered BARDSEY ISLAND, GWYNEDD 28 th June 2016 Distance travelled 122km at 16 degrees (NNE) Days since ringed 705 Additionally ringed in South Haven on 31 st July 2015 and ringed on 2 nd August 2015 were mist netted on Bardsey this year, after 313 days and 311 days respectively. Ringing recovery Originally ringed as an adult, PORTLAND BILL, DORSET 6 th July 2016 Recovered SOUTH HAVEN, SKOKHOLM 26 th July 2016 Distance travelled 238km at 304 degrees (NW) Days since ringed 20 Ringing recovery Originally ringed as an adult, PORTLAND BILL, DORSET 15 th July 2016 Recovered SOUTH HAVEN, SKOKHOLM 23 rd July 2016 Distance travelled 238km at 304 degrees (NW) Days since ringed 8 In the last four years there have been eight Portland Bill ringed birds reach Skokholm. This is the fastest recovery between the two sites to date. Ringing recovery Originally ringed as an adult, SOUTH HAVEN, SKOKHOLM 30 th July 2015 Previously recovered WOOLTACK POINT, MARLOES, PEMBROKESHIRE 26 th June 2016 Recovered PORTH IAGO, LLANGWNNADL, GWYNEDD 1 st August 2016 Distance travelled 134km at 17 degrees (NNE) Days since ringed 368 Ringing recovery Originally ringed as an adult, THE LIZARD, CORNWALL 6 th June 2016 Recovered SOUTH HAVEN, SKOKHOLM 24 th July 2016 Distance travelled 193km at 359 degrees (N) Days since ringed 48 Ringing recovery Originally ringed as an adult, THE LIZARD, CORNWALL 4 th July 2016 Recovered SOUTH HAVEN, SKOKHOLM 24 th July 2016 Distance travelled 193km at 359 degrees (N) Days since ringed 20 In the four years since Storm Petrel ringing recommenced on Skokholm there have been 17 birds ringed on the Lizard which have reached the Island, more than from any site further than 4km away. Ringing recovery P15687 Originally ringed as an adult, BURHOU ISLAND, ALDERNEY, CHANNEL ISLANDS 29 th July 2016 Recovered SOUTH HAVEN, SKOKHOLM 14 th August 2016 Distance travelled 307km at 316 degrees (NW) Days since ringed S k o k h o l m S e a b i r d R e p o r t

26 05-Apr 07-Apr 09-Apr 11-Apr 13-Apr 15-Apr 17-Apr 19-Apr 21-Apr 23-Apr 25-Apr 27-Apr 29-Apr 01-May 03-May 05-May 07-May 09-May 11-May 13-May 15-May 17-May 19-May 21-May 23-May 25-May 27-May 29-May 31-May Puffin Fratercula arctica Very Abundant Breeder 31 trapped, 4 retrapped : 5411 trapped, : 436 trapped, 11 retrapped, 1 control Pâl The first record of the season was of a lone bird drifting off North Gully on 13 th March; this was four days earlier than the first of 2015, 13 days earlier than the first of 2014 and the earliest since 28 were logged on 26 th February Not only was the first record of 2016 earlier than average, the March total of 3270 proved one of the highest on record; the only higher March totals logged since 1960 are in 2012, 4308 in 2004, 6934 in 2003 and 4504 in The bulk of the March total was made up of raft counts of 1528 on the 22 nd and 1476 on the 31 st, the latter including a minimum of 164 which landed on the Neck that evening; first landfall was noted on 2 nd April in 2015, 31 st March in 2014 and 6 th April in Daily counts were made from around the Neck each evening, from 5 th April until 31 st May, to record the pattern of colony attendance (see chart below). April counts varied dramatically with whole Island totals of 3941 on the 5 th, 3666 on the 12 th, 6692 on the 13 th, 3450 on the 18 th and 4225 on the 19 th but with no birds logged at all on the 2 nd and further lows of ten on the 3 rd, 94 on the 6 th, one on the 7 th, 122 on the 15 th and one on the 16 th. The number of Puffins seen from the Neck between 5 th April and 31 st May The transect again began from a line due north of North Haven and finished at Peter s Bay Land Air Sea For a third consecutive year the maximum whole Island count coincided with the highest count achieved from the Neck; there were 2210 birds logged from the Neck on 13 th April with simultaneous counts from the rest of the Island taking the total to 6692 for the evening. This was a remarkably similar count to the 6665 maximum logged on the considerably later date of 14 th May in 2015 and was up on the 2014 high of 5070 which was achieved on the similar date of 10 th April. The 2016 total was the highest spring count since the early 1950s (when a minimum of was logged on 22 nd April 1953 and 25 th May 1951), but well down on Lockley s pre-war spring estimates of approximately Although the whole Island counts provide a relatively consistent long-term method for monitoring the trend in numbers, how the totals reflect the Skokholm breeding population is difficult to ascertain. The Crab Bay count for the evening of 13 th April was 1610 birds, however more focused monitoring at this site revealed a study population of 82 burrows in an area which comprises approximately 10% of the colony and where less than half of the active burrows in that area were study burrows; thus we might predict a very rough minimum of 1640 pairs for Crab 26 S k o k h o l m S e a b i r d R e p o r t

27 01-Jun 02-Jun 03-Jun 04-Jun 05-Jun 06-Jun 07-Jun 08-Jun 09-Jun 10-Jun 11-Jun 12-Jun 13-Jun 14-Jun 15-Jun 16-Jun 17-Jun 18-Jun 19-Jun 20-Jun 21-Jun 22-Jun 23-Jun 24-Jun 25-Jun 26-Jun 27-Jun 28-Jun 29-Jun 30-Jun 01-Jul 02-Jul 03-Jul 04-Jul 05-Jul 06-Jul 07-Jul 08-Jul 09-Jul Bay (as active burrow distribution is apparently quite even) and expect nearly twice the number of birds to be using this area of sea than were logged during the peak whole Island count The maximum number of Puffins recorded each spring during the period A productivity plot established at Crab Bay in 2013 was used for a fourth season. The same 100 burrows individually numbered in 2013 were again used this year, with the exception of five where marker posts lost during the winter have been repositioned. Of these, 66 were seen to be occupied and were visible throughout the season (80 in 2015); productivity estimates are based on observations of these burrows. Five active burrows (7.58%) were not seen to be provisioned with fish and it is assumed that these failed at egg stage (5.00% in 2015, 6.58% in 2014). The first fish delivery witnessed this year was on 29 th May (31 st May in 2015, 3 rd June in 2014 and 30 th May in 2013), but it was not until 4 th June when fish were seen to be brought to the study plot (2 nd June in 2015 and 9 th June in 2014 and 2013). The pattern of fish delivery was rather similar to that observed in 2015, with over half of the study burrows being provisioned within a week of the first delivery to the plot. It would appear that chick hatching this season was approximately two days behind 2015, slightly earlier than in 2013 and approximately ten days earlier than in 2014 (the breeding season which followed the most severe winter storms recorded during this study) The number of study burrows which had been provisioned with fish by a particular date Although the study plot was visited for a minimum of one hour every day, it definitely cannot be assumed that the first and last fish provisioning was seen for each burrow. Indeed the 24 hour Puffin watches highlighted how many burrows are only provisioned once during daylight hours and how occasionally some chicks are not fed at all (see the second table below). Puffins can fledge having spent a minimum of 34 days as a burrow-bound chick, although this is more typically 38 days and 27 S k o k h o l m S e a b i r d R e p o r t

28 can be anything up to 60 days (Ferguson-Lees et al., 2011). However, taking into account that deliveries will have been missed, the same assumption made between 2013 and 2015 was used, namely that a chick which was seen to be provisioned for 31 days or more was of fledging size. Thus, of the 66 monitored breeding attempts, 42 (63.6%) were potentially successful (55.0% in 2015, 50.0% in 2014 and 49.4% in 2013). The following table shows the number of days between first and last fish provisioning for each of the 61 study burrows where a chick hatched. The number of days between first and last observed chick feeding. Days No. of burrows The number of fish deliveries to known active burrows during five daylight watches. No. of deliveries No. of burrows 10 June No. of burrows 17 June No. of burrows 2 July No. of burrows 14 July No. of burrows 20 July The obvious flaw with this ad hoc productivity monitoring is the potential for differences in effort between years. In an attempt to standardise effort we can remove the ad hoc observations from the data and only use sightings obtained during the daylight hours feeding/kleptoparasitism watches (see below). This is perhaps more in line with the Seabird Monitoring Handbook (Walsh et al., 1995) which states that, when monitoring Puffin productivity in colonies where the nest is inaccessible and the colony is shared with Manx Shearwaters, the most appropriate technique is, When birds are feeding large chicks, make a few watches to determine which burrows/crevices have fish taken down them. There are usually between four and five daylight watches per year on Skokholm. Calculating productivity using only three daylight watches. The first watch was between the 16 th and 28 th June (depending on the date of first fish delivery that year), the second between 30 th June and 8 th July and the third between the 12 th and 24 th July. Chicks are assumed to have fledged if present on a minimum of two consecutive watches. First fish in plot Last fish in plot Fed watch 1 & Jun 13-Aug Jun 05-Aug Jun 06-Aug Jun 14-Aug 11 Fed watch 2 & 3 Min. age 16 (17/6-2/7) 3 14 (18/6-1/7) 2 11 (28/6-8/7) 4 15 (16/6-30/6) 6 28 S k o k h o l m S e a b i r d R e p o r t Fed all 3 watches Min. age 13 (2/7-14/7) (1/7-12/7) (8/7-24/7) (30/6-13/7) 39 Min. chick age 28 (17/6-14/7) 25 (18/6-12/7) 27 (28/6-24/7) 28 (16/6-13/7) Prod. based on 2 watches 0.73 (48 of 66) 0.75 (60 of 80) 0.74 (56 of 76) 0.73 (56 of 77) The flaw with the three visit technique is that some chicks could potentially be counted as fledglings when they had only reached between 11 and 17 days of age. However it would be incorrect to assume that only those seen on all three watches went on to fledge as early hatchers could potentially have departed by the third watch whilst others may have hatched after the first watch. Although this three visit technique is more standardised than the ad hoc recording, the remarkably consistent productivity estimates of between 0.73 and 0.75 chicks per pair certainly include birds which did not fledge. With this in mind the data from five kleptoparasitism watches can be used for the period (only four watches were made in 2013). Ad hoc prod

29 Calculating productivity using five daylight watches. The first watch was between the 9 th and 21 st June (depending on the date of first fish delivery that year), the second between the 17 th and 28 th June, the third between the 1 st and 8 th July, the fourth between the 12 th and 24 th July and the last between 20 th July and 3 rd August. Chicks are assumed to have fledged if present on a minimum of three consecutive watches. First fish in plot Last fish in plot Fed watch 1 to 3, 4 or Jun 13-Aug Jun 05-Aug Jun 06-Aug 26 Fed watch 2 to 4 only Min. age 23 (10/6-2/7) 1 23 (9/6-1/7) 3 18 (21/6-8/7) 16 Fed Min. Watch 2 age or 3 to 5 28 (17/6-14/7) (18/6-12/7) 6 27 (28/6-24/7) 11 Min. chick age 19 (2/7-20/7) 22 (1/7-22/7) 27 (8/7-3/8) Prod. based on 3 watches 0.71 (47 of 66) 0.76 (61 of 80) 0.70 (53 of 76) The five visit technique counts chicks as fledged when they have only been seen as fed for between 18 and 28 days. Assuming that no food deliveries were missed during the first and last watches, birds seen only during the middle three watches were fed for no more than 39 days (in 2016) or 42 days (in 2015 and 2014) before fledging (or reached between 25 and 28 days old but did not fledge). Despite the increased effort required to do five watches rather than three, the resulting productivity values were very similar to those achieved using the three visit technique, indeed the value for 2015 goes up slightly as a bird was fed on dates either side of a watch when it was not seen to be fed. To standardise Puffin productivity monitoring on Skokholm it is recommended that the three visit technique is used from now on, bringing Skokholm in line with the other sites following the Seabird Monitoring Handbook. However the ad hoc monitoring and additional daylight watches will continue, allowing for further comparisons to be made in the future. While these productivity estimates include birds approaching fledging size, fledging success is almost impossible to ascertain reliably. Puffin chicks are particularly vulnerable when exercising their flight muscles at the burrow entrance prior to fledging and when making the journey to the sea. Great Black-backed Gulls were seen patrolling within the colonies during the chick provisioning period and were regularly observed taking young Puffins. The five 24 hour watches (made on the 10 th and 17 th June and the 2 nd, 14 th and 20 th July), were also 29 S k o k h o l m S e a b i r d R e p o r t

30 used to monitor kleptoparasitism by gulls. The study plot was again confined to the area of the 100 numbered burrow stakes at Crab Bay. On 10 th June 421 Puffins arrived to the study area with fish and of these 20 (4.75%) were successfully robbed. On 17 th June 733 birds arrived and of these 45 (6.14%) were robbed. On 2 nd July 889 birds arrived and 35 (3.94%) were robbed. On 14 th July 525 birds arrived and 28 (5.33%) were robbed. On 20 th July 242 birds arrived and 14 (5.79%) were robbed. It should be noted that these figures do not take into account the number of fish lost to gulls at sea or on the approach to the colony. The peak in monitored kleptoparasitism in 2015 was 6.15%, recorded on 9 th June, with between 1.92% and 3.67% of deliveries lost to the gulls over four further dates. In 2014 the peak was 10.69%, recorded on 21 st June, with between 0.45% and 7.21% of deliveries lost over four further dates. In 2013 an 18.4% loss was recorded on 16 th June, with between 5.25% and 10.28% of deliveries lost to the gulls on three further dates. Although the proportion of Puffins losing their fish to gulls in 2016 was lower than in 2014 and 2013 and very similar to 2015, this is again in part a reflection of more deliveries during the study period; the 45 robberies logged on 17 th June 2016 was more than on any other watch in any year, but it came on a day when there were more deliveries than during any watch in 2014 or 2013 or the watch in 2015 when 43 robberies were logged. The number of chick provisioning attempts during daylight on the 10 th and 17 th June and 2 nd July 2016, along with the number of times that gulls successfully robbed the fish (0.48%) Robbed by Herring Gull 40 4 (0.95%) Robbed by Great Black-backed Gull (3.33%) Robbed by Lesser Black-backed Gull (95.25%) Successful (0.82%) Robbed by Great Black-backed Gull 39 (5.32%) Robbed by Lesser Black-backed Gull 688 (93.86%) Successful 14 (1.58%) Robbed by Great Black-backed Gull 21 (2.36%) Robbed by Lesser Black-backed Gull 854 (96.06%) Successful 30 S k o k h o l m S e a b i r d R e p o r t

31 The number of chick provisioning attempts during daylight on the 14 th and 20 th July 2016, along with the number of times that gulls successfully robbed the fish (0.19%) Robbed by Great Black-backed Gull 27 (5.14%) Robbed by Lesser Black-backed Gull 497 (94.67%) Successful (5.79%) Robbed by Lesser Black-backed Gull 228 (94.21%) Successful 0 A colour ringing project was begun at Crab Bay in 2011 to allow an estimate of adult survival to be made each year. There were 128 birds ringed in the first year, 58 in 2012, 51 in 2013, 57 in 2014 and a further 23 were added to the scheme this year. The table below summarises the resighting data collected so far. What is apparent is that some birds are not seen every year, perhaps because they have not returned to the study plot or perhaps because their colour rings have not been seen (which may well be the case in years where the vegetation is longer); we now know for example that the 155 birds seen in 2013 was only 93.94% of the number actually alive. The survival estimates for more recent years are thus likely to be modified in the future, to take into account birds which have not yet been seen. Nevertheless, with five years of resighting data now available, we can start to look at 31 S k o k h o l m S e a b i r d R e p o r t

32 fluctuations in survival over time. Survival between the 2011 and 2012 breeding seasons was 88.28%, between 2012 and 2013 it was 96.49%, between 2013 and 2014 it was 77.78%, between 2014 and 2015 it was 91.11% and between 2015 and this season it was (a likely to be revised upwards) 86.34%. A flaw with this survivorship estimate is that colour marks were added to Puffins caught in flight, individuals potentially resident in areas not visible to researchers. A better estimation of survivorship may therefore come from looking for birds previously seen in the field (thus discounting individuals in the year after ringing); thus of 113 known to be alive in 2012, 110 (97.35%) survived to 2013, of 165 alive in 2013, 129 (78.18%) survived to 2014, of 168 alive in 2014, 154 (91.67%) survived to 2015 and of 205 alive in 2015, 177 (a likely to be revised upwards 86.34%) survived to this season. The most striking feature of these survivorship estimates is the substantial drop noted after the severe winter wrecks; it remains to be seen how often such drops in survival can occur before the spring raft counts show a decline in overall numbers. Survival in adult Puffins. The average survival figure is based on the number of birds ringed in the preceding year plus the number of previously ringed birds known to be still alive; for example 165 birds are now known to have been alive in 2013, of a 2012 total of 171 (58 ringed in 2012 plus 113 known to be alive). Survival after a one year establishment period means that birds have been seen within the study area before (and are therefore assumed to be located in visible positions); birds ringed in the preceding year are therefore excluded from the calculations. Year of ringing Total ringed Seen in 2012 Alive in 2012 % survival 2012 Seen in 2013 Alive in 2013 % survival 2013 Seen in 2014 Alive in 2014 % survival 2014 Seen in 2015 Alive in 2015 % survival 2015 Seen in 2016 Alive in 2016 % survival Total Average Survival Survival after one year S k o k h o l m S e a b i r d R e p o r t

33 The end of July saw fewer birds arriving with fish, although there were still 31 deliveries to the west of Crab Bay Hide in one hour on 31 st July and large numbers of adults lingering offshore included minimums of 3400 on the 20 th and 4200 on the 24 th. There were 620 birds logged on 1 st August, 149 on the 2 nd, 100 on the 3 rd and 120 on the 4 th followed by counts of between 44 and ten from the 5 th to the 12 th. The six birds logged on 13 th August included one delivering fish to a South Coast burrow and at least one which, in one hour, made three food deliveries to study burrow 29 in Crab Bay; these were the last observed fish deliveries of 2016, three days earlier than the last of 2015, ten days earlier than in 2014 and one day earlier than in A lone bird sat on the sea with fish on 14 th August eventually departed Crab Bay without making landfall; this was the last record of the year. There were no September sightings for the first time since Razorbill Alca torda Abundant Breeder 37 trapped (including 34 pulli) : 9220 trapped, : 83 trapped, 1 retrapped, 2 controls Llurs There were no Razorbills present on five days during the first week of staff presence in 2016, with counts of 775 on 29 th February (when 20 were on the cliffs) and 274 on 4 th March (when 11 were on the cliffs) the only birds noted. The average March daycount was virtually identical to 2015 and well up on 2014 (the year following the winter wrecks), although there were still lows of between 24 and zero on nine dates. The majority of the birds logged during the highest March counts were on the sea; March peaks of 1640 on the 7 th, 1986 on the 18 th, 1942 on the 19 th and 1880 on the 21 st included only 422, 395, 235 and 293 cliff occupying birds respectively. In April there were four dates when no birds were logged, the latest being the 16 th, and a further seven dates when fewer than 70 birds were present, the latest being the 26 th. The only four figure counts in April were 1098 recorded on the 4 th, 1596 on the 5 th, 1200 on the 13 th and 1190 on the 19 th. Although fewer than 650 birds were logged on each of the last seven days of the month, the first egg was found on Middlerock on the 27 th ; this was the same date as in 2015 but 16 days earlier than the first of 2014 (probably again a consequence of the winter storms preceding that breeding season). On 12 th May a Razorbill was watched as it took ten minutes to drown another adult before it spent a further 20 minutes gouging and ripping at the throat of the dead bird (photograph below); there was no sign of anything such as fishing debris which could have joined the birds and the victor eventually swam further out to sea where it washed and preened. Another adult Razorbill was taken by a Great Black-backed Gull on the same date and a bird on 16 th May was found covered in Fulmar oil and with an open throat wound. At least one Razorbill was killed during the mid-june rock slip in the Quarry, although a loaf of 24 individuals above the fall area on 21 st June perhaps suggests that more birds were impacted. Six study plots, established in 2002, were visited on ten dates between 29 th May and 11 th June and every adult in suitable breeding habitat was counted. There was a 17.7% drop in numbers compared 33 S k o k h o l m S e a b i r d R e p o r t

34 with 2015 and the mean total of 260 adults on ledges was the lowest of the last four years (although still the fifth highest since the plots were established). The largest decline was observed at Little Bay Point where there was a 32.4% drop in numbers to the lowest mean total since At Twinlet there was a 16.1% drop in numbers to the lowest mean since 2010 and at Middlerock a 12.3% drop in numbers took the mean to its lowest since 2007 and its second lowest on record. Conversely the North Gully mean was the same as that logged in 2015 and the highest ever. The plot counts are seemingly affected by the weather in some years; in the unsettled June of 2012 the total fluctuated between 164 and 338 birds whereas the 2015 spread was the tightest on record with a prolonged period of high pressure coinciding with the lowest standard deviation of the last four years. The weather this season was again calm and dry, but the standard deviation and the difference between the lowest and highest plot counts were comparatively large; the reason for the increased variance in plot counts this year is unclear, however it is perhaps not connected to a difference in breeding success as a similar proportion of attempts had failed in the productivity plots during this study period as in the preceding year. Another factor which may come into play in the future is that the six Skokholm study plots are all areas shared with Guillemots, a species currently increasing rapidly both in the plots and on Skokholm as a whole and which may be competing with Razorbills for space in the plots. The total number of adult birds in all six study plots (as an average from ten visits) and the totals from the four largest plots (as an average from ten visits) Whole Island counts were made between the 2 nd and 5 th June, including a boat based count on the 3 rd. This is the fourth year running that access to a boat has been available, inevitably leading to higher but more accurate whole Island counts; in 2012 rough seas meant that there was no opportunity for a boat based count and it was concluded that there remains a section of North Coast that was missed, while other parts of the North Coast and Bluffs were counted less accurately at a distance (Gillham and Yates, 2012). A whole Island total of 2242 adults in suitable breeding habitat this season was 5.9% down on the 2382 logged in 2015 but was still the third highest total yet recorded on Skokholm (2.3% down on the 2013 total but 55% up on the mean). The whole Island totals, mean plot totals and the percentage of the Island totals made up of study plot birds Also the range of plot counts since 2012 and the standard deviation observed over the ten plot visits since (*includes a boat based count) Island * * 2052* 2382* 2242* Plots Range ±SD Plot % S k o k h o l m S e a b i r d R e p o r t

35 The drop in the whole Island count was thus not as marked as that observed in the plots, perhaps in part due to the fact that the whole Island count occurred in a period when the counts in the plots were higher; two of the three highest plot counts in 2016 came in the period 2 nd to 5 th June when the whole Island counts were being undertaken. The period of rapid population growth witnessed on Skokholm in recent years has seemingly plateaued, a halt almost certainly linked in part to the winter wrecks of which in Pembrokeshire impacted this species more than any other The total number of Razorbills (adults on ledges) recorded on Skokholm since 1970 and the number of birds within the study plots since Productivity monitoring was undertaken for a fourth year running and the same two study sites were used, one a cliff below the Neck Razorbill Hide where 30 incubating pairs were located by 29 th May and one a site among the Bluffs boulder slope where 39 egg sites were marked on 24 th May. On the cliff there were 16 failures at egg stage (one fewer than in 2015 when 30 sites were also monitored); although the reason for failure was typically unclear, one site deserted by adults contained a cracked egg. Elsewhere on the Island, eggs were seen to be taken by Ravens, Great Black-backed Gulls, and most commonly by Herring Gulls. Nine cliff attempts failed at small chick stage, three with a medium sized chick and one with a large chick. Thus only one chick left the Neck plot in 2016; the resulting productivity figure of 0.03 jumplings per pair is the lowest yet recorded at either site, down on the 0.17 logged at this plot in 2015 and well down on the 0.36 and 0.77 recorded here in 2014 and S k o k h o l m S e a b i r d R e p o r t

36 29-May 31-May 02-Jun 04-Jun 06-Jun 08-Jun 10-Jun 12-Jun 14-Jun 16-Jun 18-Jun 20-Jun 22-Jun 24-Jun 26-Jun 28-Jun 30-Jun 02-Jul 04-Jul 06-Jul 08-Jul 10-Jul 12-Jul 14-Jul 16-Jul 18-Jul Among the Bluffs boulders nine pairs failed at egg stage, with three of the eggs found abandoned rather than disappearing. A further pair failed at chick stage, with a medium sized youngster found dead in its nest crevice. There were 29 pairs which produced a jumping sized chick; the resulting productivity value of 0.74 jumplings per pair was the highest yet recorded at this site, up on the 0.29 of 2015, the 0.44 of 2014 and the 0.55 of This was thus the third year running that productivity has been higher in the boulder plot than on the cliff, although the 0.77 chicks per pair logged at the cliff in 2013 is the highest productivity observed at either plot in any of the last four years. For a fourth year running the last of the breeding attempts within the boulders were concluded before the last of the attempts on the cliffs; this perhaps reflects a tendency for large chicks among the boulders to move away from the egg site, whilst cliff chicks have little room for movement. Combining the productivity figures for the cliff plot and the boulder plot to give an indication of overall productivity on Skokholm can be achieved in two ways. Averaging the two sites, as recommended in the Seabird Monitoring Handbook (Walsh et al., 1995), gives a 2016 productivity estimate of 0.39 chicks per active site, a figure up on the 0.21 of 2015, very similar to the 0.40 of 2014 and down on the 0.66 of Combining the data from the two plots produces similar productivity estimates (as the number of study pairs in each plot is similar); combined plot data gives a 2016 productivity estimate of 0.43, compared with 0.23 in 2015, 0.39 in 2014 and 0.67 in It seems likely that a four year mean of 0.42 chicks per pair is not sufficiently high to maintain the rapid population growth recorded since The number of adults on ledges within three of the plots (standard study period in black). Middlerock Guillemot Cliff North Gully For a third year running counts at three of the study plots were continued beyond the normal study period to ascertain the pattern of colony attendance during the remainder of the breeding season (see chart above). There were fluctuating numbers in all three colonies and regular peaks when the totals were presumably augmented by the return of failed adults or the presence of more nonbreeding birds; interestingly these peaks were again consistent between colonies suggesting that the returning birds respond to the same environmental cues. The first jumpling had departed the productivity plots by 22 nd June, four days earlier than the first of 2015, and all but two productivity chicks had departed by 3 rd July, a jumping period very similar to that observed in 2015 but considerably earlier than in the late 2014 season when only 60% of young had jumped by 7 th July. There was a similar departure of adult birds, with numbers dropping rapidly from 2 nd July. There were only double figure counts from 14 th July (8 th July in 2015, 17 th July in 2014 and 14 th July in 2013) and these had dropped to single figure counts by the 25 th (22 nd July in 2015, 27 th July in 2014 and 24 th July in 2013). Despite the appearance of a freshly hatched chick at Little Bay Point on 20 th July, adults were last seen on the cliffs on 24 th July, the same date as in 2015, seven days earlier than in S k o k h o l m S e a b i r d R e p o r t

37 and three days earlier than in The four birds recorded over two dates in August was a typically low monthly total and in September there were 237 noted over 18 dates, all but four being logged from the 12 th. There were 109 birds logged over 16 dates in October and 228 over 16 dates in November. The September and November totals were the highest for over a decade whereas the October total was the lowest of the last four years. In contrast to the Guillemots, no Razorbills were seen back on the cliffs before the departure of staff on 26 th November. Further large auks were present at sea during the autumn but they remained unidentified due to their distance from the Island; there were 679 in September, 2055 in October and 2628 in November. Ringing recovery K27390 Originally ringed as a chick, PUFFIN ISLAND, ANGLESEY 6 th June 2011 Recovered THE BLUFFS, SKOKHOLM 22 nd May 2015 (sic) Finding condition At colony but not necessarily breeding. Metal ring read in field Distance travelled 199km at 206 degrees (SSW) Days since ringed 1446 Guillemot Uria aalge Abundant Breeder 1 pullus trapped, 2 controls : 1023 trapped, : 2 pulli trapped, 12 controls Gwylog As was noted last year, the pattern of early colony attendance was often different to that exhibited by the Razorbills; this was first evident on 29 th February when only 44 Guillemots rafted with over 700 Razorbills and some Razorbills took to the ledges when Guillemots did not. The March Guillemot total of was the highest on record and an indication of things to come; despite 15 lows of between zero (on seven dates) and 82, there were seven counts of over 2000 birds and highs of 2326 on the 8 th, 2680 on the 21 st and 3367 on the 22 nd, the latter being the highest March count on record. Birds were first seen on the ledges on 7 th March, when 1613 were present, there were seven further dates when the majority of ledges were occupied and five dates when only a small number of birds landed on the cliffs (birds were thus on ledges on 13 dates compared with ten in 2015, seven in 2014 and four in 2013). There were the customary departures for the sea in April, with no birds logged at all on four dates to the 16 th and nine further counts of 51 or fewer birds including 15 on the 27 th which was the last significant pre-breeding departure (13 mass departures matches that observed in April 2015, this compared with 19 in 2014 and 2013). Whereas colony attendance continued to fluctuate during the first half of May in 2013 and 2014, as in 2015 this season saw consistently high totals from the 3 rd (this year following a low of only 386 individuals on the 2 nd ). The first eggs to be seen in 2016 were logged on 5 th May, three days later than the first of 2015 but ten days earlier than in 2014 and eight days earlier than in S k o k h o l m S e a b i r d R e p o r t

38 The six study plots were counted on ten dates between 29 th May and 11 th June. The mean total from all plots was 943 adults on ledges, 9.1% up on 2015 and 5.2% up on the previous record set in The mean total for the majority of plots has proven to be remarkably consistent over the last four years; for example at Middlerock there was an average of 63 adults on ledges in 2013 and 2014 and 64 in 2015 and 2016; at North Gully the mean was 271 in 2013 and 276 this year. Nevertheless, in all but one instance, each 2016 plot total proved the highest on record (albeit at levels very similar or equal to those recorded recently); the exception was Guillemot Cliff where there was an average of 180 adults on ledges this season compared with 181 in The largest increase occurred at the Steep Bay plots where in 2013 there were 123 adults on ledges, in 2014 there were 116, in 2015 there were 120 and this year there were 140. The 2016 study period was again dominated by high pressure and saw a low count of 887 on 29 th May and a high of 1003 on 5 th June (the first four figure count ever made in the plots); the ten visit range of just 117 birds was the tightest of the last five years and the standard deviation (40.25) was the second lowest (behind 2013 when the standard deviation was and the range was 126 birds). The largest range logged of late came in the wet and unsettled June of 2012 when the total fluctuated between 530 and 746 birds, a range of 217 individuals. The total number of adult birds in all six study plots (as an average from ten visits) and the totals from the four largest plots (as an average from ten visits) The whole Island totals, mean plot totals and the percentage of the Island totals made up of study plot birds Also the range of plot counts since 2012 and the standard deviation observed over the ten plot visits since (*includes a boat based count) Island * * 3512* 3603* 3949* Plots Range ±SD Plot % Whole Island counts were made from the land between the 2 nd and 5 th June and calm weather allowed for a boat based count on the 3 rd. Boat-based surveys allow some areas to be monitored which cannot be viewed from on the Island and enable closer access to some areas which can normally only be viewed at a distance. A total of 3949 adults in suitable breeding habitat was a 9.6% increase on the 2015 count and the highest total yet recorded on Skokholm. This is the largest increase in the population noted since the significant increases observed between 2010 and The proportion of the whole Island count made up of study plot birds dropped for a seventh consecutive year, as might be expected if the whole Island population is increasing at a similar rate 38 S k o k h o l m S e a b i r d R e p o r t

39 29-May 31-May 02-Jun 04-Jun 06-Jun 08-Jun 10-Jun 12-Jun 14-Jun 16-Jun 18-Jun 20-Jun 22-Jun 24-Jun 26-Jun 28-Jun 30-Jun 02-Jul 04-Jul 06-Jul 08-Jul 10-Jul 12-Jul 14-Jul 16-Jul 18-Jul to that observed in the plots. These counts of individuals on ledges potentially include incubating adults, some of their partners, failed breeders, non-breeding adults and younger birds yet to breed; a correction factor is thus sometimes adopted to convert the count to an estimate of breeding pairs (Harris et al., 2015). A 2015 survey on Skokholm found the correction factor to be 0.64, a figure similar to the 0.67 widely adopted in previous studies (see the Skokholm Seabird Report 2015) The total number of Guillemots (adults on ledges) recorded on Skokholm since 1928 and the number of birds within the study plots since The first chicks to be seen this season were found at Middlerock, North Gully and the Stack on 6 th June, one day earlier than the first of 2015, seven days before the first of 2014 and eight days before the first of Productivity, calculated at between 0.55 and 0.61 chicks per pair in 2013 and 0.6 in 2007, was not assessed in 2016 in accordance with recommendations from the Islands Conservation Advisory Committee. Chicks were observed jumping from 21 st June and the number of adults recorded in the plots dropped rapidly from 587 on 30 th June to 488 on 1 st July, 277 on the 5 th, 158 on the 8 th, 99 on the 14 th, ten on the 16 th and the last four birds were seen on 17 th July (the 18 th in 2015, 22 nd in 2014 and 28 th in 2013). For a third year running, birds were slower to depart at North Gully, although this may in part reflect the larger breeding population at this site. Whole Island counts mirrored those made at the plots and a lone brooding bird near North Gully on 23 rd July was the last to be seen ashore (25 th July in 2015). There were only 47 birds noted at sea during the last eight days of July and a further 47 were logged over 14 dates in August including calling youngsters heard from the Lighthouse and peaks of ten on the 13 th and five on the 11 th and 30 th The number of adults on ledges within three of the plots (standard study period in black). Middlerock Guillemot Cliff North Gully 39 S k o k h o l m S e a b i r d R e p o r t

40 September counts were typically low, with 268 birds logged over 20 dates and peaks of 96 on the 13 th and 52 on the 14 th, although a further 679 unidentified large auks were noted at sea during the month (57 Guillemots and 606 unidentified auks were logged in September 2015). The 45 birds noted over eight dates in October echoed the 25 birds over five dates in October 2015 but a further 2055 distant, unidentified auks was well up on the 2015 total of 672. Although a return of Guillemots to the breeding ledges in early winter is to be expected, there was no record of this behaviour on Skokholm between 2000 and 2014, despite the fact that staff did not depart until 24 th November in 2014 and 16 th November in In November 2015 up to 540 birds returned to the cliffs on five dates. This season also saw birds return to the cliffs on five dates, although fewer birds were counted; there were 164 above the Jogs on 3 rd November, two there on the 11 th, 141 ashore on the 13 th (130 above the Jogs, six at Little Bay and five at Guillemot Cliff), 216 on the 14 th (again with the majority above the Jogs but with 72 at Twinlet) and 36 on the 15 th (30 at Twinlet and six at the Jogs). Droppings on the rocks at North Gully on the latter date suggested that some birds had departed the cliffs prior to the arrival of staff that morning. Interestingly, as in 2015, the majority of Guillemot colonies were not reoccupied during this period; if it is assumed that birds take to the same ledges which they occupy during the breeding season, then it would seem likely that the returning neighbours must first congregate at sea to coordinate their visit. A return to the colony outside of the breeding season, with the risk of being predated, must have a substantial benefit; it has been suggested that the return may be to secure the best breeding ledges and thus secure the best mate (Harris et al., 2006), but birds ashore may also use less energy than those at sea (Humphreys et al., 2007). A further 261 birds were logged at sea over 14 November dates before the departure of staff on the 26 th and 2628 unidentified auks were further offshore. Ringing recovery Left leg yellow darvic (faded) with black 73X Originally ringed as a chick, SKOMER ISLAND, PEMBROKESHIRE 1998 Previously recovered as an adult (bridled), SKOMER ISLAND, PEMBROKESHIRE 2005 Previously recovered as an adult (bridled), MIDDLEROCK, SKOKHOLM 19 th June 2013 Previously recovered as a breeding adult (bridled), MIDDLEROCK, SKOKHOLM 30 th April 2014 Recovered as a breeding adult (bridled), MIDDLEROCK, SKOKHOLM 25 th June 2016 Finding condition Ring read in field Distance travelled 4km at 163 degrees (SSE) Days since ringed approximately 6583 Ringing recovery Left leg green darvic with white 352, Right leg X05852 Originally ringed as a chick, PAYNE S LEDGE, SKOMER ISLAND, PEMBROKESHIRE 1992 Previously recovered as a non-breeding adult, PAYNE S LEDGE, SKOMER ISLAND 1996 Previously recovered as a non-breeding adult, PAYNE S LEDGE, SKOMER ISLAND 1997 Previously recovered as an adult, PAYNE S LEDGE, SKOMER ISLAND S k o k h o l m S e a b i r d R e p o r t

41 Previously recovered as a winter plumage adult, EAST OF NORTH GULLY, SKOKHOLM 30 th June 2015 Recovered as a winter plumage adult, EAST OF NORTH GULLY, SKOKHOLM 28 th May 2016 Finding condition Ring read in field Distance travelled 4km at 163 degrees (SSE) Days since ringed approximately 8694 An unusual record of a bird over 20 years of age which does not seemingly attain breeding plumage. Lesser Black-backed Gull Larus fuscus Gwylan Gefnddu Leiaf Abundant Breeder previously very abundant breeder 40 trapped (including 32 pulli), 3 retrapped, 1 control : 12,085 trapped, : 330 trapped, 8 retrapped, 11 controls The birds logged in total this March was up on the of 2015 and the of 2014, however peak counts were again down; March highs of 1203 on the 13 th, 1059 on the 25 th and 1279 on the 28 th were approximately 300 birds down on the last two years. The larger communal roosts recorded in previous years were generally absent, with the majority of March counts being of birds on territory; the largest roosts away from the breeding colonies were a minimum of 160 in the Bog on the 2 nd and 125 by North Pond on the 9 th. The number of birds within the colonies fluctuated considerably during the day, for example at Frank s Point there were 106 birds on the morning of 21 st March but 221 roosted there that evening. The GPS trackers fitted by the British Trust for Ornithology in 2014 (funded by the Department of Energy and Climate Change), revealed when birds first returned for the breeding season. When GPS tagged Lesser Black-backed Gulls made their return to Skokholm in 2015 and Birds marked with an asterisk were regular visitors to Skokholm during the winter months. Birds marked with a dagger suffered from tag malfunction. Tracker Number Overwintering Location 2015 (same in 2016 unless marked ) Departed Overwintering Location Departed Mainland Europe Arrived to Skokholm Pembrokeshire 1/2 * Female 4023 Pembrokeshire 8/2 *? 5004 Pembrokeshire 9/2 * Female 5003 Central Spain 19/2 24/2 27/2 Female 5000 Northwest France 22/2 28/2 4/3 Female 5001 S & Central Spain 1/3 DEAD 3/3 DEAD 4/3 DEAD Female 4024 South Spain 28/2 23/2 7/3 26/2 8/3 27/2 Male 5013 NW Morocco 10/3 11/3 Female 5021 Midwest Portugal 3/3 11/3 12/3 Female 5009 South Spain 5/3 21/2 11/3 25/2 12/3 26/2 Female 5010 Northwest Spain 22/2 11/3 13/3 Female 5002 Northwest France 9/3 11/3 11/3 11/3 16/3 12/3 Female 5006 Northwest France 17/3 11/3 17/3 11/3 17/3 12/3 Female 4000 NW Morocco 7/3 14/3 16/3 27/3 18/3 27/3? 5017 Midwest Portugal 5/3 26/3 12/3 28/3 19/3 8/4 Male 5022 Central Spain 1/3 20/3 16/3 31/3 20/3 2/4 Male 4009 Midwest Portugal 28/3 19/3 3/4 25/3 4/4 26/3 Male 5015 NW Morocco 28/3 20/3 11/4 26/3 13/4 28/3 Male Of 12 tracker birds which returned with functioning tags, three returned to Skokholm regularly during the winter, a further two had returned by 7 th March, a further two by 12 th March, a further Sex 41 S k o k h o l m S e a b i r d R e p o r t

42 three by 28 th March and the final two had arrived by 8 th April. Although the three birds which overwintered in Pembrokeshire returned first, the return dates of the other birds were again not seemingly influenced by overwintering site; some of the longer distance migrants returned before those which had wintered in northwest France. Four of the last five birds to return were male (with the fifth unsexed); as in 2015, the majority of tracked females returned to Skokholm before the males. Although the dates on which birds departed their winter quarters were in some cases quite different to 2015 (departing between 13 days earlier and 21 days later and on average 0.9 days later), and the dates on which they arrived to Skokholm were often also quite different (arriving between 15 days earlier and 19 days later and on average 1.9 days earlier), in all cases where tracking data was available, birds overwintered in very similar areas to those visited in Comparing the winter range of three Lesser Black-backed Gulls over successive winters. Red tracks are those made between the 2015 and 2016 breeding seasons and yellow tracks are those made between the 2014 and 2015 breeding seasons. Google Imagery 2014 TerraMetrics Numbers logged in April were relatively consistent, although there were occasional mass departures and low counts of 514 on the 10 th and 619 on the 18 th. A single egg was found at the Top Tank on 25 th April, nine days before the first of 2015 (when two nests at North Pond contained three eggs and three contained a single egg), one day later than the first of 2014 (when a single egg was found) and eight days before the first of 2013 (when two nests contained two eggs). Vantage point counts of all the inland breeding colonies and a full census of the coast nesting pairs were made between the 18 th and 21 st May, during which 1209 apparently incubating adults (aia) were located (the lowest total in over 50 years, down on the 1275 of 2015, the 1407 of 2014 and the 1476 of 2013). Walk through counts were undertaken at eight subcolonies on the 20 th to check the accuracy of the point counts. A comparison of the number of apparently incubating adults and the number of nests containing eggs suggested that there was a discrepancy (see table below). Unlike last year, when in one plot the number of incubating birds was overestimated by the vantage point count (presumably due to resting guard birds or non-breeders appearing as if they were incubating 42 S k o k h o l m S e a b i r d R e p o r t

43 or due to birds sitting on empty nests), this year saw all of the vantage point counts equal or underestimate the number of sitting birds. The rapidly shrinking colony to the north of the Wheelhouse was believed to contain five sitting birds during the eye count and this proved to be the case on the walkthrough. The remaining seven plots contained more nests with eggs than the number of apparently incubating adults, presumably due to incubating birds being hidden in vegetation; this was most apparent to the south of Spy Rock where there were 52.27% more nests containing eggs than aia, to the south of the Top Tank ridge where there were 35.71% more nests with eggs than aia and to the west of Orchid Bog where there were 32.65% more nests with eggs than aia. On average across the eight plots there were 18.18% more nests containing eggs than were predicted during the vantage point counts (650 with eggs compared with 550 aia during the counts); in 2015 there were 25.00% more nests with eggs than picked up during the vantage point counts and in 2014, when the vegetation was particularly low, there were 12.89% more. A correction factor of 1.18 (650/550) was thus applied to inland vantage point plots containing similar dense vegetation to that encountered in the walk through plots, but not to the cliff counts and areas of very short sward. The corrected total for the inland plots was 575 pairs. This, combined with the 650 nests with eggs encountered on the walkthroughs and the 172 birds incubating in open areas, gave a 2016 whole Island total of 1397 pairs. This was the lowest total for over 50 years, 6% down on the 1486 pairs recorded in 2015 and down on the 1565 and 1476 pairs logged in 2014 and 2013 respectively. A comparison of vantage point counts (of apparently incubating adults) and walk through nest counts, along with a summary of nest contents. *how many more/less active nests (containing eggs) were present than the number of incubating birds seen (%). Vantage point count Walkthrough count Empty/ With egg(s) Percentage of empty nests Difference between counts* Egg count Eggs per nest with eggs Spy Rock S 44 aia 78 nests 11/ % % Top Tank N 94 aia 102 nests 2/ % +6.38% Top Tank S 70 aia 110 nests 15/ % % North Pond 71 aia 97 nests 18/ % % Orchid Bog 49 aia 92 nests 27/ % % Frank s Point 126 aia 145 nests 9/ % +7.94% Bread Rock 91 aia 159 nests 56/ % % Wheelhouse 5 aia 6 nests 1/ % = Total 550 aia 789 nests 139/ % % A University of Gloucestershire project this year attempted to use a drone to assess the number of incubating Lesser Black-backed Gulls, thus removing the need for walk through counts which inevitably disturb the colony. Although incubating birds were tolerant of the drone (more so than loafing or roosting birds), identifying which birds were sat on nests proved to be difficult. This project will be reported upon elsewhere. 43 S k o k h o l m S e a b i r d R e p o r t

44 As the walk through plots mirrored those used in 2015, a direct comparison can be made. The most striking decline occurred to the north of the Wheelhouse (to the south of Medicine Rock Wall) and to the west of Orchid Bog; these sites contained 119 nests with eggs in 2015 but only 70 this year (a 41.2% decline). The North Pond plot contained 86 nests with eggs in 2015 but only 79 this year (a drop of 8.1%). Perhaps surprisingly given recent declines, three plots saw small increases this year; the Bread Rock plot increased by 2% from 101 to 103 nests with eggs, the Frank s Point plot increased by 2.3% from 133 to 136 nests with eggs and the Top Tank North plot increased by 14.9% from 87 to 100 nests with eggs. Although it should perhaps be no surprise that the Skokholm breeding population is declining given the poor productivity witnessed for many years, there may be further reasons for a decline in the number of breeding adults. This year saw a considerable increase in the number of dead adults found on Skokholm; there were 25 dead adults found between 4 th March and 1 st August Although two of the birds probably died from fighting (one had a broken wing) and two were found dead on nests which contained single eggs (and perhaps therefore died due to complications with egg laying), it seems likely that the remaining 21 birds died due to disease. The period before death was characterised by very lethargic behaviour and a fine shaking of the head before a loss of limb coordination. Whereas the majority of dead birds had clean vents, some had dirty yellow vents. Although one fledgling showed similar symptoms, the nine dead juveniles found was a typical number and a third calendar year bird died with a broken wing. Over the period the count of empty nests varied from 11-44% of the total number of nests, with a mean of 22.7% (Thompson, 2007). With the exception of the area near the Top Tank, where less than 2% of nests were found to be empty (mirroring 2015 when this site also contained the lowest number of empty nests), and the Frank s Point colony which contained less than 7% empty nests (also the second lowest number of empty nests in 2015), the number of empty nests located at each walk through site in 2016 was within the range of that found by Thompson. Overall, of 789 visited nests, 17.62% were found to be empty (17.30% in 2015, 16.32% in 2014 and 19.84% in 2013). It was unclear whether the empty nests were second nests made by the pairs present, nests which had been robbed of eggs or nests where the adults had yet to lay. The breeding season was certainly a protracted one, with the first chicks located at the Top Tank on 20 th May (6 th June in 2015, 23 rd May in 2014 and 30 th May in 2013), other chicks just hatching on 25 th June (nine days before the first fledgling took to the wing) and with a late fledgling near Orchid Bog on 4 th September (still with primary feathers in pin). It would thus seem likely that at least in some cases the latter two of the above three options may have been the case, meaning that the Skokholm breeding population is actually higher than that suggested above. However, even if we wrongly assume that all empty nests belonged to additional pairs, the predicted Island total would only be 1657 pairs (an extra 260 pairs). The total number of Lesser Black-backed Gull breeding pairs Control measures started in 1984 (destruction of nests) and stopped in S k o k h o l m S e a b i r d R e p o r t

45 The breeding success of the Skokholm Lesser Black-backed Gull population has been low for many years and is a major factor contributing to the observed population decline. The poor success has been linked to a reduction in food availability during the chick rearing period, primarily due to changes in the fishing industry (for example in Thompson, 2007). Studies on Skomer in the 1970s and 1980s suggested that earthworms were an important adult food item during the egg incubation period but that adults switched to taking fish during the chick provisioning period. The decline in reproductive success has been attributed to a failure to make this switch in food, with regurgitate studies suggesting that chicks are fed on earthworms in years of poor productivity. Circumstantial evidence suggested that hot, dry summers resulted in productivity being further reduced, perhaps due to earthworms being less available in dry conditions (Thompson, 2007). However the 2014 tracking data suggested that the majority of adult birds did make a switch to maritime feeding during the chick rearing period, a switch which may have been responsible for the improved productivity witnessed that season. In 2015, a year which saw productivity drop to a typically low level, the tracking data suggested that far fewer birds made the switch to maritime feeding in June and July (although it was not known whether the tracked birds had chicks); 16 of the 17 birds tracked spent the majority of the chick feeding period foraging inland and followed nearly every foraging trip to sea with a foraging trip inland. The GPS tags, which have revealed so much about the behaviour of Skokholm breeding Lesser Black-backed Gulls, were this year removed as they are reaching the end of their useful lives; the tags were removed during the egg incubation period meaning that there is no chick period data for Only the colonies at Frank s Point and to the north of the Top Tank proved suitable for productivity monitoring in 2016; long vegetation in the clearings within colonies, probably due to continued low Rabbit numbers, made ring resighting particularly challenging in In an attempt to increase the number of resightings, the colonies were re-entered this season (rather than observing fledglings at a distance with a telescope, a method which was failing to locate any rings). A simple calculation was again used, (number of fledglings ringed x number checked for rings on second visit)/number of 45 S k o k h o l m S e a b i r d R e p o r t

46 birds seen to have rings on second visit, to predict the number of fledglings within the area. There were 19 birds ringed on the first visit to the productivity plots and the most productive return visit yielded seven resightings and 13 unringed birds. It was thus predicted that the 236 nests with eggs counted at these sites produced fledglings, which results in a productivity figure of 0.23 fledglings per pair. Observations from elsewhere also suggested that productivity in 2016 was up on the previous year. Although fledglings at North Pond could potentially have come from anywhere on Skokholm, there were seven counts in 2016 in excess of 100 individuals and peaks of 115 fledglings on 30 th July, 123 on 3 rd August and 110 on 5 th August; there was a maximum of 68 fledglings recorded at North Pond on the 30 th and 31 st July 2015 but 127 in the July of a more productive Lesser Black-backed Gull productivity estimates The number of Lesser Black-backed Gulls roosting on North Plain and in the vicinity of North Pond July August September North Plain and the area around North Pond again proved to be the usual site for the largest post breeding roost, with smaller numbers congregating around the coast and at South Pond. Numbers using the site gradually increased during July from 180 on the 5 th, to 230 on the 12 th and 337 on the 13 th and 15 th, from when there were a further nine July counts over 300 and peaks of 429 on the 20 th, 394 on the 24 th and 476 on the 30 th. As in the previous three years, the majority of the largest roost counts were logged in August, however the overall number of birds logged during the month was very similar to July (contrasting with the period when considerably more roosting birds were logged in August than July). Peak August counts were 483 on the 6 th, 429 on the 13 th, 421 on the 14 th and 441 on the 18 th, totals well down on the 2015 high of 581 on the 14 th, the 2014 high of 943 on the 21 st and the 2013 high of 680 on the 11 th. Counts dropped off considerably in early September, as they did in 2015 and 2013, a drop which was not seen until the middle of the month in Overall in this three month period there were birds logged at the North Pond and North Plain roosts, 9.4% fewer than in 2015, 51.0% fewer than in 2014 and 31.2% fewer than in 2013; this decline in roost numbers reflects both a steady reduction in the number of breeding adults and each year s breeding success. A small number of birds remained on Skokholm in October with records on all but two dates, ten or fewer birds logged on 26 dates and highs of 16 on the 4 th and 21 on the 16 th. There were records on 17 November dates to the 25 th, with ten or fewer birds logged on 12 dates and highs of 79 on the 16 th and 33 on the 17 th and 18 th ; a brief increase in numbers was also logged in the November of 2015 when 98 were counted on the 21 st, however prior to this the last larger late season count was the 80 birds logged on 2 nd December S k o k h o l m S e a b i r d R e p o r t

47 Ringing recovery Left leg blue darvic with orange DTV, Right leg FH21424 Originally ringed as an adult, STOKE ORCHARD, GLOUCESTERSHIRE 22 nd November 2008 Previously recovered as an adult, PINTO, MADRID, SPAIN 7 th January 2009 Previously recovered as an adult, near HEMPSTED, GLOUCESTERSHIRE 23 rd November 2010 Previously recovered as an adult, NORTH PLAIN, SKOKHOLM 29 th July and 13 th August 2013 Previously recovered as an adult, NORTH PLAIN, SKOKHOLM 29 th March and 2 nd September 2014 Previously recovered as an adult, NORTH PLAIN, SKOKHOLM 13 th March 2015 Recovered as an adult, NORTH PLAIN, SKOKHOLM 22 nd July 2016 Finding condition Ring read in field Distance travelled 220km at 266 degrees (W) Days since ringed 2784 This bird has only ever been seen in unseasonal winter plumage on Skokholm. Ringing recovery GA00721 reringed Left leg yellow darvic with black 7P:W, Right Leg GR98242 and fitted with GPS device #5002 Originally ringed as a chick, BARDSEY ISLAND, GWYNEDD 24 th June 1996 Previously recovered as an adult, TOP TANK, SKOKHOLM 16 th May 2014 Previously recovered as an adult, TOP TANK, SKOKHOLM May 2015 Recovered as an adult, TOP TANK, SKOKHOLM May 2016 Finding condition GPS device #5002 removed Distance travelled 122km at 196 degrees (SSW) Days since ringed 7266 This bird spent much of the winter in northwest France and returned to Skokholm on 12 th March. Ringing recovery Black darvic with white 5AW8 and metal ring D7734 Originally ringed as a subadult male, CHOUET LANDFILL, GUERNSEY 24 th May 2013 Previously recovered as a subadult, FIGUEIRA DA FOZ, COIMBRA, PORTUGAL 8 th November 2013 Previously recovered as a subadult, VIL DE MATOS LANDFILL, PORTUGAL 8 th November 2013 Recovered as an adult, DUMBELL BAY, SKOKHOLM 13 th May 2016 and 29 th June 2016 Finding condition Ring read in field Distance travelled 311km at 320 degrees (NW) Days since ringed 1085 and 1132 Our GPS tagged birds, along with an additional 48 non-tagged controls, were all fitted with yellow darvic rings with a black alpha-numeric code (number/letter:w e.g. 5A:W) in The colour ring is on the left leg and a BTO metal ring on the right. The darvic rings have yielded a fantastic number of field resightings; the 73 ringed birds have produced 110 separate resightings of 26 different individuals (including nine birds with GPS trackers). The following table summarises resightings received of non-gps tagged birds since similar tables were published in the 2015 and 2014 Seabird Reports. As has been shown by the British Trust for Ornithology GPS tracking project (see above) and at other British Trust for Ornithology tracking sites (Ross-Smith, pers. comm.), Lesser Black-backed Gulls show a high degree of wintering site fidelity. This is also reflected by the colour ringing data with 11 birds having been resighted at the same location in successive winters; records of returning birds have come from several sites in Portugal and Spain along with France and Morocco. Darvic Ring Location Country Date 8H:W GR98250 Malaga Harbour Spain 21/02/15 8K:W GR98252 Rymer Barn Pig Field, Suffolk UK 21/12/15 8X:W GR98258 Combarro-Poio, Pontevedra Spain 05/10/16 9C:W GR98262 Colmenar Viejo Landfill, Madrid Spain 13/08/16, 17/09/16, 29/10/16 9J:W GR98265 Barbate Harbour Spain 23/01/16 9Y:W GR98276 Portimao Harbour, Faro Portugal 28/12/15 47 S k o k h o l m S e a b i r d R e p o r t

48 Larus hybrid Larus fuscus x Larus argentatus Scarce Breeder An apparent hybrid was again holding territory with a Lesser Black-backed Gull above South Haven, the same site occupied in at least the previous three seasons (see photographs in the 2015 and 2014 Seabird Reports). As in 2015, the pair were regularly seen together during the course of the season and fed together from regurgitated food on 29 th May, however they were not seen with a nest, eggs or young. A different hybrid was again present on the Neck, although this bird was seemingly not paired. Whether these hybrids are remnants of cross-fostering experiments (500 Herring Gull and 400 Lesser Black-backed Gull chicks were raised by adults of the wrong species between 1963 and 1966 with the result that they frequently paired with the species of the adopting parents) or whether they are the result of natural interbreeding, is unclear. The latter may certainly be the case on occasion; an apparently pure male Herring Gull was watched as it mounted an apparently pure female Lesser Black-backed Gull in Crab Bay on 30 th April, although these birds were not paired and had same species partners incubating on nests positioned in close proximity to each other. Herring Gull Larus argentatus Common Breeder abundant breeder in the 1970s 11 trapped, 2 retrapped : 13,164 trapped, : 57 trapped, 10 retrapped Gwylan y Penwaig Numbers fluctuated in March, with birds frequently feeding away from Skokholm but returning to roost on the Neck. Peak counts of 261 on the 13 th, 229 on the 22 nd and 230 on the 25 th were down on the previous three years, although April counts were well up; there were 14 April counts in excess of 300 birds and highs of 512 on the 7 th and 466 on the 25 th. The 7 th April count included 113 subadult birds, substantially more than the number of subadult Lesser Black-backed Gulls logged and perhaps a reflection of Herring Gull productivity in recent years being considerably higher than that of their relative. Nest building was first witnessed on 3 rd March and the majority of pairs had nests by 15 th April, however it was not until 17 th April that the first egg was found (25 th April in 2015, 14 th April in 2014 and 18 th April in 2013). Whole Island counts took place between the 16 th and 18 th May when 314 active nests were located and an additional eight nests were found on the back of the Stack from a boat on 3 rd June. The number of breeding pairs (where data exists). The 1970s peak was attributed to the exploitation of local fish waste and the decline to botulism (Thompson, 2007) A whole Island total of 322 active nests was an 11.4% increase on the 289 nests of 2015, 10.3% up on the mean (292.0 ±sd 30.04), the highest count since 2009 and the second highest count since The number of breeding pairs has apparently stabilised close to that seen in the 48 S k o k h o l m S e a b i r d R e p o r t

49 1930s, prior to the huge peak in numbers recorded in the 1970s (the mean was ±sd 17.47). Counts in May were bolstered by birds feeding in Broad Sound, with the May peak of 694 on the 30 th including a minimum of 500 birds feeding there; although no such flocks were logged in 2015, the May 2014 peak included a minimum of 250 birds in Broad Sound. A dead adult on North Plain on 17 th June had perhaps succumbed to the same disease seen in some Lesser Black-backed Gulls. The first flying fledgling was logged on 30 th June (10 th July in 2015, 2 nd July in 2014 and 7 th July in 2013). Checks of the Neck productivity plot in early July, where 169 pairs had established nests (140 in 2015 and 146 in 2014), located between 139 and 146 fledging sized young. Taking the highest count produces a productivity estimate of 0.86 fledged young per pair, a figure 30.3% up on the 0.66 logged in 2015 and 17.8% up on the mean (0.73 ±se 0.06). The only higher productivity estimates logged since 1995 have been 1.35 fledglings per pair in 1996, 0.89 in 2001 and 1.15 in Herring Gull productivity remains consistently higher than that of the closely related Lesser Black-backed Gull, circumstantial evidence suggesting that this may be due to differing feeding habits. Additionally Great Black-backed Gulls seemingly target the coastal nesting Herring Gulls less frequently than they do the inland gull colonies, although predation by Greats was again witnessed around the Neck this year. It would appear that current Herring Gull productivity levels are sufficient to sustain a stable breeding population at this time. The number of breeding pairs and productivity estimates (average number of fledglings per sample pair) Numbers fluctuated in August following the mass departure of both adults and fledglings in late July; there were lows of 36 on the 15 th, 18 on the 17 th and 27 on the 22 nd but highs of 209 on the 3 rd, 154 on the 10 th and 146 on the 14 th when birds returned to the Island to feed on swarming ants. As in the 49 S k o k h o l m S e a b i r d R e p o r t

50 previous three seasons few Herring Gulls visited Skokholm in September, with 38 or less logged on each date bar the 14 th and 15 th when birds feeding offshore bolstered counts to 138 and 89 respectively. There were daily records in October and four counts in excess of 100 individuals peaked at 118 on the 2 nd and 28 th ; although slightly down on 2015, October counts were thus well up on 2014 and 2013, primarily due to an increase in the number of birds feeding with the Broad Sound gull flock. November counts were remarkably similar to 2015 with 4454 birds logged to the 25 th (4466 in 2015) and a high of 588 on the 25 th (585 on the 21 st in 2015). There were further November 2016 highs of 455 on the 13 th, 321 on the 17 th and 387 on the 24 th when birds joined the large feeding flock of smaller gulls which forms in Broad Sound. Great Black-backed Gull Larus marinus Fairly Common Breeder and Common Visitor 48 trapped (including 33 pulli), 1 control : 219 trapped, : 187 trapped, 7 retrapped, 3 controls Gwylan Gefnddu Fwyaf This year saw spring totals at the Bog roost very similar to the previous two years, with a March high of 48 on the 9 th and April highs of 52 on the 7 th and 58 on the 30 th ; the sizable roost which formed at the Bog during the early part of the 2013 season and which peaked at 213 individuals on 3 rd April was also much reduced in 2015 (when there was a March high of 37 and an April high of 63) and in 2014 (with a March high of 34 and an April high of 54). A whole Island census on 19 th May located 91 pairs on territory (85 nests with eggs were found) and a further two territories and nests were encountered over the following nine days. A total of 93 pairs was a 12% increase on 2015 and the most yet recorded on Skokholm. The additional pairs found this year all occupied areas some distance from the path network and the two pairs which nested on the wall to Little Bay Point in 2014 remained at the sites further from paths occupied in 2015; although this perhaps supports the theory that disturbance may limit the breeding population (a theory proposed during the period of Island closure when numbers increased dramatically), the continued increase in numbers is occurring during a period with high guest numbers. The increasing population is in part been driven by a high adult return rate; of 21 adults bearing rings in 2015, 19 (90.48%) returned to the same territories this year and two were not seen. As all of the adults present on Skokholm this breeding season were checked for rings, it seems likely that this is a very good approximation of survival. Of 23 adult birds ringed in 2014, 19 (82.6%) returned in 2015 and none of the four missing birds were encountered this year either. The number of Great Black-backed Gull breeding pairs (where data exists). Control of numbers started in 1949 (destruction of both nests and adults) and stopped in The Great Black-backed Gulls are spectacular apex predators and an exciting component of the Skokholm seabird assemblage, however it is important that we monitor the impact of these high 50 S k o k h o l m S e a b i r d R e p o r t

51 breeding numbers on the Manx Shearwater population. Whereas the majority of shearwaters are probably taken at dawn and occasionally during the day, Great Black-backed Gulls were again seen to be hunting at night, with a bird on a very dark 30 th April watched as it stalked amongst thick vegetation. Dead Manx Shearwaters were counted for a third consecutive year, the vast majority of which had been predated by Great Black-backed Gulls; a total of 3697 corpses, comprising 2299 adults and 1398 youngsters, were marked this year (4026 comprising 2702 adults and 1324 young in 2015 and 4219 comprising 2931 adults and 1288 young in 2014). Although the number of located corpses declined this year, the number of dead youngsters was the highest of the three year study, probably due to a combination of low Rabbit numbers and high gull numbers. The number of dead birds being found remains a relatively small proportion of the Skokholm shearwater population, however it seems likely that continued growth of the Great Black-backed Gull population will increase their impact on the shearwaters (see the Manx Shearwater section for further details). Although evidence collected at the nests suggested that the gulls are primarily exploiting natural food, particularly seabirds and Rabbits, up to 14 individuals were seen to be collecting discards from lobster potting vessels on the 4 th and 14 th April, 13 th May and 21 st June, a remarkable 33 fed around a potting vessel off Crab Bay on 5 th June and four accompanied fishermen using rod and line from a private boat on 28 th May; an important step to understanding the Great Black-backed Gull population will be to discover if such anthropogenic food sources are regularly exploited, particularly during periods of low seabird or Rabbit numbers when they may increase survival. The first two eggs observed this year were found at the Bog on 12 th April; the first two of 2015 were found on the 19 th, the first single of 2014 was found on the 10 th and two full clutches were found on the 25 th in Of 40 monitored nests, 12 pairs failed at the egg incubation or small chick stage, eight pairs fledged a singleton, 13 pairs fledged two and seven pairs fledged three. There were thus 55 fledglings and a productivity figure of 1.38 fledged young per monitored pair. Although productivity was thus 16.9% down on 2015, it was 26.6% up on the mean of 1.09 and 21.1% up on the mean (1.14 ±se 0.12). Productivity estimates (average number of fledglings per sample pair) In an effort to further understand observed population growth, a Great Black-backed Gull colour ringing project was begun in 2014, in part to shed light on juvenile survival and recruitment. Of 44 fledglings ringed in 2014, 24 (54.55%) have been resighted subsequently and four have been found dead. Ten of the birds (22.73%) definitely survived their first full year and four (9.09%) have survived 51 S k o k h o l m S e a b i r d R e p o r t

52 their second years. Of 52 fledglings ringed in 2015, 20 (38.46%) have been resighted subsequently, one has been found dead and eight (15.38%) have survived their first full year. These survival estimates are more accurate for the birds ringed in 2014 as there has been longer to look for them, however clearly these figures do not give an exact measure of juvenile survival. Only time will tell whether this study provides a good estimate of survival to breeding age, something which may well be dependent on how many birds return as adults to Skokholm or Skomer (where they should be seen) as opposed to other less studied breeding sites. Two youngsters have so far returned to Skokholm, one in the April following its fledging and one as a two year old. Although the resighting records will be somewhat biased by a preponderance of birders at the main roost sites in Cornwall, it seems likely that there is a genuine southerly bias to the movements of young Skokholm Great Black-backed Gulls (see map below). All of the records below were received since a similar table was published in the 2015 Seabird Report. Darvic Ring Location County Age Date W:022 HT94867 Gann Estuary Pembrokeshire Adult 02/09/16 W:036 HT94898 The Gannel, Newquay Cornwall Second Winter 29/03/16 W:037 HT94899 The Lizard Cornwall Second Winter 08/04/16 W:039 HT94878 Gothian Sands LNR Cornwall Third Winter 05/10/16 W:048 HT94909 Hayle Estuary Cornwall Third Winter 25/10/16 W:055 HT94917 Nevern Estuary Pembrokeshire Third Winter 16/12/16 W:073 HT94930 Nevern Estuary Pembrokeshire Third Winter 14/12/16 W:074 HT94931 Gann Estuary Pembrokeshire Adult 02/09/16 W:081 HT94938 Gann Estuary Pembrokeshire First Winter 27/03/16 W:083 HT94940 Duncannon Harbour Wexford, IRELAND First Winter 16/01/16 W:086 HT94947 Camel Estuary Cornwall First Winter 22/03/16 W:089 HT94950 Hayle Estuary Cornwall First Winter 20/01/16 W:089 HT94950 Gwithian Cornwall First Winter 11/04/16 W:094 HT94957 Radipole Lake, Weymouth Dorset First Winter 24/03/16 W:094 HT94957 Axe Estuary Devon First Winter 24/03/16 W:094 HT94957 Nevern Estuary Pembrokeshire Second Winter 15/10/16 W:098 HT94961 Kerbinigou Beach Finistere, FRANCE First Winter 29/12/15 W:098 HT94961 Camel Estuary Cornwall First Winter 29/03/16 W:099 HT94962 Saundersfoot Harbour Pembrokeshire Second Winter 02/09/16 W:099 HT94962 Wiseman s Bridge Pembrokeshire Second Winter 16/12/16 W:103 HT94966 The Lizard Cornwall Second Winter 07/07/16 W:107 HT94970 St Ouens Pond Jersey, CI First Winter 28/03/16 W:107 HT94970 L Eree Bay Guernsey, CI Second Winter 14/08/16 W:109 HT94972 The Lizard Cornwall Second Winter 23/08/16 W:116 HT94976 The Lizard Cornwall Second Winter 21/07/16 W:120 HT94980 The Lizard Cornwall Second Winter 07/07/16 W:122 HT94945 Penzance Cornwall First Winter 28/01/16 W:124 HT94955 Camel Estuary Cornwall Second Winter 14/12/16 W:129 HT94985 Looe Island Cornwall First Winter 08/01/16 W:140 HT94995 Camel Estuary Cornwall Adult 03/12/16 W:148 MA37803 Gann Estuary Pembrokeshire Adult 10/09/16 W:159 MA37817 Nevern Estuary Pembrokeshire First Winter 10/10/16 W:162 MA37820 Budleigh Salterton Devon First Winter 30/09/16 W:171 MA37830 Rosslare Wexford, IRELAND First Winter 13/12/16 A roost of up to 56 birds, but more typically less than 20, frequently formed in the Bog during the breeding season, totals down on 2015 when there were regular counts of up to 40 birds and a peak 52 S k o k h o l m S e a b i r d R e p o r t

53 of 82 on 27 th May; the majority of birds were in full adult plumage, although there were up to five subadults regularly in May and up to eight in June. The increase in breeding pairs this year may in part be responsible for the decline in breeding season roosts. The first fledglings were recorded on 30 th June, however, with the exception of roosts of 38 on 7 th July, 41 on 4 th August and 39 on 8 th August, it was not until 21 st August that larger communal roosts formed. North Plain, North Pond and the area to the north of the Sugarloaf again proved the most popular post-breeding roost sites, with peak counts of 62 on 21 st August, 99 on the 22 nd and 128 on the 31 st. The first fledgling to be recorded away from Skokholm accompanied a parent at the Gann on 2 nd September, a youngster which was found dead back on Skokholm on 18 th October (one of two colour ringed fledglings found dead during the autumn (of 28 ringed)). A second fledgling had reached the Nevern, Newport by 17 th September and the first youngster to be recorded away from Pembrokeshire was at Budleigh Salterton, Devon on 30 th September (one had reached the Lizard, Cornwall by 15 th September in 2015). In September there were six counts in excess of 200 birds, with peaks of 232 on the 13 th (including 125 in the North Plain roost), 247 on the 14 th (142 North Plain) and 224 on the 20 th (130 North Plain); although well below the September 2013 peak of 355, the 2016 counts were up on 2015 (with the exception of the 249 logged on the 22 nd in 2015) and well up on the September 2014 maximum of 52. There were seven October counts in excess of 100 birds, with highs of 175 on the 3 rd (101 North Plain), 155 on the 4 th (112 North Plain) and 152 on the 17 th (92 North Plain), although there were fewer than 23 birds logged on each date from the 19 th. Seven birds were again following a potting vessel on 8 th October. There were 18 or fewer birds logged on each November date to the 25 th, with the exception of 44 on the 16 th (20 North Pond) and 26 on the 17 th (19 on the Neck); November counts were thus the second lowest of the last four years and again well down on the 2013 highs of 270 and 243. The movements of Skokholm ringed Great Black-backed Gulls Google Imagery 2014 TerraMetrics 53 S k o k h o l m S e a b i r d R e p o r t

54 Ringing recovery MA31816 Originally ringed as a chick, ST TUDWALS ISLAND WEST, GWYNEDD 24 th June 2015 Recovered SKOKHOLM 22 nd September 2015 (sic) Finding condition Dead with a broken neck Distance travelled 134km at 204 degrees (SSW) Days since ringed 90 The most likely cause of this fatal injury was another Great Black-backed Gull. Literature Cited Betts, M. (1992) Birds of Skokholm. Dyfed Wildlife Trust Betts, M. (1994) Storm Petrels on Skokholm Unpublished report for the Dyfed Wildlife Trust Brooke, M. de L. (1990) The Manx Shearwater. Poyser Brown, R. and Eagle, G. (2013) Skokholm seabird report Online report for the Wildlife Trust of South and West Wales Brown, R. and Eagle, G. (2014) Skokholm seabird report Online report for the Wildlife Trust of South and West Wales Brown, R. and Eagle, G. (2015) Skokholm seabird report Online report for the Wildlife Trust of South and West Wales Ferguson-Lees, J., Castell, R. and Leech, D. (2011) A Field Guide To Monitoring Nests. BTO Gillham, J. and Yates, L. (2012) Skokholm Island Annual Report Unpublished report for the Wildlife Trust of South and West Wales Gynn, E. (1984) Dead shearwaters on Skokholm. Bulletin of the Friends of Skomer and Skokholm 7:10-11 Harris, M., Heubeck, M., Shaw, D. and Okill, D. (2006) Dramatic changes in the return date of Guillemots Uria aalge to colonies in Shetland, Bird Study 53: Harris, M., Heubeck, M., Newell, M. and Wanless, S. (2015) The need for year-specific correction factors (k values) when converting counts of individual Common Guillemots Uria aalge to breeding pairs. Bird Study 62 (2): Humphreys, E.M., Wanless, S. and Bryant, D.M. (2007) Elevated metabolic costs while resting on water in a surface feeder: the Black-legged Kittiwake Rissa tridactyla. Ibis 149: Smith, S., Thompson, G.V.F. and Perrins, C.M. (2001) A census of the Manx Shearwater Puffinus puffinus on Skomer, Skokholm and Middleholm, west Wales. Bird Study 48: Sutcliffe, S.J. (2010) Storm Petrels on Skokholm. Unpublished review report for the Countryside Council for Wales and the Wildlife Trust of South & West Wales Sutcliffe, S.J. and Vaughan, D. (2011) Storm Petrel monitoring on Skokholm. Unpublished report for the Wildlife Trust of South and West Wales Thompson, G.V.F. (2003) Storm Petrel census on Skokholm in Contract science report number 673, Countryside Council for Wales Thompson, G.V.F. (2007) The natural history of Skokholm Island. Trafford Publishing Vaughan, D. and Gibbons, D.W. (1996) Storm Petrel census on Skokholm Island, Report to Countryside Council for Wales, RSPB and Dyfed Wildlife Trust Vaughan, D. (2001) Storm Petrel census of Skokholm Island, Pembrokeshire, Report to JNCC and the Wildlife Trust of South and West Wales Walsh, P.M., Halley, D.J., Harris, M.P., del Nevo, A., Sim, I.M.W. & Tasker, M.L. (1995) Seabird monitoring handbook for Britain and Ireland. JNCC/RSPB/ITE/Seabird Group, Peterborough Wood, M.J., Taylor, V., Wilson, A., Padget, O., Andrews, H., Buche, B., Cox, N., Green, R., Hooley, T- A., Newman, L., Miquel-Riera, E., Perfect, S., Stubings, E., Taylor, E., Taylor, J., Moss, J., Eagle, G. & Brown, R.D. (2017) Repeat playback census of breeding European Storm Petrels on the Skokholm and Skomer SPA in Unpublished report for Natural Resources Wales 54 S k o k h o l m S e a b i r d R e p o r t

55 Fulmar attacking Herring Gulls Ian Peters, Manx Shearwater among Thrift Chris Perrins, Storm Petrel chick Sam Hobson, Puffling Kevin Maskell, Herring Gull and Puffin Kevin Maskell, Fighting Puffins Richard Coles, Great Black-backed Gull (with Lesser chick) mobbed by a Lesser Black-backed Gull and two Herring Gull Richard Coles and Herring Gull with chick Richard Coles. All other photographs Richard Brown and Giselle Eagle Report compiled by Richard Brown and Giselle Eagle This work was funded in part by Natural Resources Wales 55 S k o k h o l m S e a b i r d R e p o r t