Halton Skylark Report Contents. Introduction 3 Methodology 5 Results 7 Analysis 8 Conclusion 10 Appendices; I 12 II 13

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2 Halton Skylark Report 2007 Contents Introduction 3 Methodology 5 Results 7 Analysis 8 Conclusion 10 Appendices; I 12 II 13 2

3 Introduction The Skylark Alauda arvensis has traditionally been held in the popular imagination by the people of Britain. It has one of the widest ranges of any bird in the UK and could once be seen on any patch of open land, from coastal saltmarshes to moorland and in arable fields up and down the Country. Although the bird is non-descript brown, it can be easily recognised by its distinctive call and flight pattern. In the early spring, males can be seen taking off vertically from the ground and soaring to height of up to 100m. The song it lets forth is a loud, distinct chirrup, often described as sounding liquid, and will be continued for several minutes as the bird hovers high above it s territory. Sometimes phrases mimicked from other birds can be heard within the song. This behaviour is used by male birds in order to establish territories for the coming breeding season, which lasts throughout the summer and may produce up to four broods. At first sight, the Skylark is an unexciting brown and grey streaked bird with a buff belly. Its most distinctive feature is the crest on its head which the males are able to erect, although the crest is often pushed flat by windy conditions. The wings are pointed at the tip and flap rapidly as the bird takes off and propels itself vertically. The overall length of a skylark is cm, making it a similar size to a swallow (but lacking the long tail). Figure 1, a Skylark Jeff Clarke The British population of skylarks is predominately resident all year round, although some breeding grounds in Scotland are vacated in the winter. Come autumn, flocks of skylark can often be seen congregating on stubble fields, their numbers swelled by over wintering northern European birds. Skylarks will not be found near established trees and large bushes, and so are restricted to very open land, which is why they are found in places like arable fields and saltmarsh. Once the spring is warm enough to commence breeding, a nest is formed from a hollow on the ground and lined with leaves. The female will usually lay a clutch of three to four eggs (although this number can vary from one to six), and only she will incubate them. When hatched (after about two weeks incubation) the 3

4 chicks will be fed by both parent birds on insects at first, but after a week, a variety of plant matter will be introduced into the diet. By twenty five days, the juveniles will have become fully independent. Further broods in the same year will be raised in the same breeding territory. The ideal breeding habitat for skylarks is open countryside with vegetation cover of about 20-25cm in height, and which will provide plenty of seeds and other vegetable food (such as shoots) throughout the summer. In this type of habitat, skylarks are able to raise two to three broods during the breeding season, which is the minimum number needed to sustain the population (RSPB). During the last quarter of the twentieth century the population of skylarks in Britain has declined so much that it is listed as a Red Species (species of most conservation concern) by the ornithological organisations of the United Kingdom. Elsewhere in Europe there have been declines too, and the bird is a European species of concern, although the global population as a whole is not thought to be under threat. The decline in numbers is thought to be linked to a reduction in the ideal breeding habitat, which has reduced both breeding density (per ha of habitat) and the number of successful broods by each pair per year. Data produced by the Royal Society for the Protection of Birds (RSPB) and British Trust for Ornithology (BTO) suggest that there has been a steep decline in British population of Skylarks since the 1970s. The RSPB suggests that this is as much as 75% of the population between 1972 and BTO statistics show that during and since the 1990s the decline has continued, but at a slower rate. This trend is similar to that of many farmland birds and researchers associate it with changes in farming practices. One of the main factors causing decline is thought to be a switch from spring-sown cereal crops to autumn/winter-sown cereal crops. The basic reason why this is thought to be a problem is that during the summer breeding months, winter-sown cereals will have grown too tall and dense for skylarks to nest in. Many birds may then attempt to nest in the tractor-tracks running across the field, resulting in greater mortality when farm machinery is in operation. Also, cultivation of autumn/wintersown crops does not leave stubble during the following autumn, which is in important food source for skylarks. Other factors associated with agricultural intensification include greater use of herb and pesticides which remove weed seeds and invertebrate food sources. Many farms now also produce more silage, rather than hay, to feed livestock on which is not advantageous for skylarks because it will be cut before the end of the breeding season, or at least before the skylarks have had chance to reproduce enough times to support the population. Such a sharp decline in the number of birds has lead to the skylark becoming a Biodiversity Action Plan species (BAP species) for the United Kingdom. Within the BAP process are local BAPs (LBAPs) which used to remedy the losses for locally sensitive species. In the Cheshire region, farmland birds as a whole, and the skylark in particular have become LBAP species. As a result, Halton Borough Council have included the skylark in its own list of LBAP species. Within the Borough of Halton, there are a number of habitat areas where skylarks are known to exist. Halton has a high proportion of land dedicated to housing and 4

5 industry, habitat types which the BTO cite as being of low value for skylarks (towns have lowest relative skylark frequency out of thirteen habitat types). However, Halton also has areas of farmland, including arable farmland, a habitat which has a relatively high frequency of skylarks. A figure on the amount of farmland will be available on completion of a Phase One Habitat survey, the results of which are due in Other significant habitats in Halton which can accommodate skylarks include grass and parkland, and the estuarine saltmarsh. The Halton skylark BAP outlines specific targets and measures aimed at conserving the skylark population in Halton. The key target is a 20% increase in breeding pairs by In order to complete this task, the Borough is currently taking a number of actions (e.g. promoting countryside stewardship schemes to local farmers) which will provide more areas of suitable habitat for skylarks. As well as these practical conservation and habitat creation processes, a system of recording and monitoring is also provided for under the BAP. All existing records for the species in Halton (and the rest of the Cheshire region) are continuously being aggregated on the record database, but record itself has been commissioned to undertake a programme of skylark recording for The record scheme has targeted specific areas in an attempt to quantify breeding areas for skylarks in Halton. This is to be combined with a data search of the record database and analysis of the results forms the Halton 2007 skylark report. Methodology The record database was searched in order to map the distribution of skylark records held for Halton. In addition to this desktop study, areas within in the Borough were identified for survey work. These areas were known to support skylarks already, but further data collection was required in order to produce an estimate of the number of breeding territories for each area. The areas that were chosen for study were of differing habitat types and were managed in different ways. Table 1 outlines the areas selected for study. Table 1. Areas selected for skylark surveying Location name Description Habitat type(s) Fields by Hale Lighthouse, Hale, near Widnes. Astmoor Saltmarsh An area of agricultural land under high level stewardship, flanked to the north by Hale Village and to the south by the Mersey estuary. Immediately east and west are more agricultural fields of various types and areas of marsh. An area of saltmarsh to south of the Mersey estuary, which undergoes little or no management. It is sometimes inundated by the estuary during Arable fields of cereal crop (to the east) and rape (to the west) Saltmarsh 5

6 Keckwick / Sandymoor area Fields around Preston-onthe-Hill, Summer Lane Wood. particularly high tides. An area, predominantly of farmland and open grassland. The area as a whole is bounded by the estate of Sandymoor and the Daresbury Science Park. The area is over 1.5km (1mile) west-east diameter and includes land earmarked for development and Keckwick Balancing Lake. An area comprised of farmland only, apart from an area of young plantation woodland. A preliminary survey over the whole area produced only one recording of skylarks, near the plantation woodland (Summer Lane Wood), and hence only this site was selected for further study. Grassland, woodland, pasture and arable. Young plantation woodland (maximum tree height, approximately 1.5m) For a map of these areas in relation to the rest of the Borough of Halton, see appendix I. The surveying schedule commenced on March 5 th 2007 and ceased on May 24 th This was designed to sample the earlier part of breeding season, as male birds are establishing their territory. Due to restraints on resources, a full survey throughout the whole season (February to August) could not be considered, nor could more frequent visits to each site. There were no surveys on wet weather days, but where possible the next day was used instead. For a breakdown of all survey days, see appendix II. Each survey commenced at dawn in an attempt to record whilst the birds are at their most active and to control for variability of the sunlight and conditions associated with the progression of time. A survey event itself consisted of a walk around the particular location, marking the geographical position of a skylark on the map every time one was seen. Other than the presence of the skylark, other attributes that were noted include; the abundance (i.e. the number of birds), whether the bird(s) were singing males and any other notable behaviour. In order to record abundance as accurately as possible, the count for the number of birds for that particular specific location (in practice this is an individual six figure grid reference) is taken as the maximum number of birds seen at any one time which negates the possibility of counting the same bird more than once. 6

7 Where birds were noted as being singing males, it was taken as an indication of a breeding territory. Singing males were birds exhibiting the classic territorial behaviour (noted earlier in the introduction), i.e. prolifically singing whilst hovering very high above the ground. Each survey event lasted roughly the same amount of time, although there was some difference because on days where there was little bird activity to record (e.g. during very overcast conditions) the fieldwork took less time to complete. At the end of a survey event, a map was produced with various marks denoting the position of skylarks. This was then digitally processed in the office in order to hold the information on the record database. This information was then used in conjunction with geographical information system (GIS) software to produce distribution maps. During the field work, land use was noted and this was transferred digitally, using the GIS, to produce area polygons of different land uses to be used in the analysis of results. Analysis consisted of three main features; 1. Mapping the abundance to determine hotspots for skylarks within the Borough 2. Comparing the abundance of skylarks recorded in the survey with land usage also recorded in the survey 3. An estimate of the number of breeding territories within Halton Results The combined data search and survey yielded individual records, of which 211 were generated by this survey. Records of skylarks could be found in every ward or parish in Halton. In order to make statistical comparisons across different areas, the average abundance of skylarks was calculated for each individual spatial reference. Each record is stored with some data on the abundance of skylarks that were seen at the time (on occasion this can be hard to quantify, but as with the standard for ornithological recording the abundance is always the maximum number of birds seen in any one place at any one time). In order to compare the results from different areas, an estimate of the average number of skylarks per Km 2 was carried out. This cannot be done simply by dividing the total number of records for each habitat by the area of that habitat because each record can represent several birds. There is also the problem that some areas have more records than others, i.e. the recording effort is higher in those places, and this needs to be taken into account. In an attempt to control for these factors as much as a possible, the following calculation was carried out for each habitat type / land use surveyed. Av. birds per record Av. records per day = Av. birds per day Av. Birds per day / area of habitat type (Km 2 ) = Av. Birds per Km 2 for that habitat type on any given day. 7

8 The results of this process are presented in Table 2 (below). Table 2. Results of calculations for average number of birds in each habitat type Land Use Type Average Birds Average Total Area Average Birds per Record Records per Day Surveyed (Km 2 ) Km 2 Cereal Grassland Rape Saltmarsh Scrub (former grassland planted with saplings in ) Wood Analysis A simple map of the position of skylark records across the Borough of Halton would show a wide spread of skylark sites, with records congregating around some areas. However, this form of analysis is heavily biased by recorder effort. The term recorder effort refers to the amount of recording visits recorders make to the same area, compared with the rest of the Borough. In the case of this survey, there were three heavily recorded areas and these are likely to stand out on a map of overall skylark records. In an attempt to reduce this bias, the average abundance of skylarks can be used. This is measure of how many birds are sighted on average for the records in a particular area. By dividing Halton into 100m squares and colouring it according to the mean skylark abundance for that square, a map can be produced showing hotspot 8

9 areas where many skylarks can be found together, as shown by figure 2 (below). Figure 2, a map displaying the average abundance of skylarks per 100m in Halton Figure 2 shows four particularly notable areas for skylarks in Halton. Oxmoor Wood and ponds is a local nature reserve and as such has a high level of biodiversity overall. Widnes Warth is a saltmarsh area, a habitat type that has been strongly associated with skylarks in Halton and although not in active conservation management, it has high wildlife value. The fields around Keckwick and Sandymoor are open farmland, the traditional stronghold for skylarks in Britain, but have undergone severe declines in the number of breeding birds in the last thirty years. To investigate possible trends in the numbers of skylarks further, the survey results can be used to show the average abundance of skylarks in particular land uses. These values are compared in the chart below (figure 3) Figure 3, a Chart Comparing the Average Abundance of Skylarks per Km 2 Different Land Uses in Halton for Estimate of Skylarks per sq Km for Different Habitats / Landuses in Halton Skylarks / sq Km Scrub Saltmarsh Grassland W ood Rape Cereal These results seem to show, as expected from the hotspot map, that the skylark population is not evenly spread across the various types of land usage across Halton. It is no surprise to see that grassland is rich in skylarks as this is often a preferred habitat (see introduction). It is also not surprising to note the fact that saltmarsh is also a habitat relatively rich in skylarks, given the points on the hotspot map and what is known about the preferred habitat for skylarks. This would seem to make more sense and would show saltmarsh and grassland to be the main the strongholds for skylarks in Halton. The figure calculated for woodland habitat is also anomalous, but this is very quickly explained after a quick investigation of those records. In actual fact a few birds were seen flying over a small area of woodland, and cannot be 9

10 associated with woodland because skylarks are known only to inhabit areas clear of trees. The high value for scrub is attributed to a survey area of plantation woodland where the trees are still only saplings. This was classified as scrub because the trees are of such little stature, but inevitably they will grow up to produce a woodland habitat. Some time before this happens, the area will no longer be suitable for skylarks, so although currently this is an important area for skylarks it is only temporary. It would not usually be expected for scrub to be strongly associated with skylarks, especially dense continuous scrub, but in this instance the shrubbery was very sparsely planted, giving the area many of the characteristics of a grassland. Using the same method as before to control for recording effort the estimated number of breeding pairs; Av number of singing males per record Av records per day in survey area = av singing males per day in survey area = 4.42 per day in 2.15 Km 2 Total breeding territories = (av. Singing males / survey area) area of Halton suitable for skylarks. The area of Halton suitable for skylarks was estimated by subtracting the area of land unsuitable, i.e. woodland, roads, houses and water, from the total areas of Halton. (4.42 / 2.15) ( ) = per day in all Halton = 59 breeding territories This estimate will certainly have a degree of inaccuracy, but is a best effort considering the constraints of the limited area that the survey was able to cover. The estimate was conducted in conjunction with local ornithologists for two reasons. The first was to make sure the calculation appeared valid to people who know the area best, and they felt it would provide a reasonable representation of skylarks in Halton. The second reason was to make sure the eventual figure seemed valid. Had the figure that was produced seemed very unlikely, then the methodology would have had to be reviewed. Conclusions The overall conclusion of this report is that grassland and saltmarsh habitats are very important for skylarks in Halton, more so than the agricultural land types such as arable areas that were once the mainstay of the British skylark population. This may have significant implications for the future management of skylark areas and the skylark BAP. Estuarine saltmarsh in Halton maybe affected greatly by urban developments around the Upper Mersey Estuary area, and it may be that if Halton wishes to fulfil the BAP population targets for skylarks, that any damage to the skylark population on the saltmarshes is either reduced or mitigated. 10

11 Many of the grasslands surveyed by for this report are in areas that are under consideration for housing development. Obviously, if these areas are built on then the skylark population in Halton will be affected adversely, unless other habitat types are managed more effectively for skylarks in place of those lost. The estimate of breeding territories would seem quite low when one considers that there is an estimated 1.8 million breeding pairs in Britain, according to the BTO. However, Halton itself has a proportion of urban cover compared to the rest of the United Kingdom, reducing the amount of suitable habitat. Perhaps the most important use of the breeding pair estimate is that the methodology and the value itself set a precedent for future population estimates, and provide a way of monitoring future population change, as Halton attempts to fulfil its BAP. In conclusion, it has been shown that saltmarsh and grasslands are very important for skylarks in Halton, and that crop fields also provide suitable habitat for skylarks. If the grasslands and saltmarshes are affected by future developments, then other habitats such as crop fields will have to support a greater population. Perhaps extension of farming stewardship schemes or other agri-environmental schemes will help promote this. 11

12 Appendix I Map of areas covered by survey. 12

13 Appendix II Table of dates of visit to various areas. Date 05/03/ /03/ /03/ /03/ /03/ /03/ /04/ /04/ /04/ /04/ /04/ /04/ /4/ /05/ /05/ /05/ /05/ /05/ /2007 Astmoor Saltmarsh Hale Sandymoor / Keckwick Area Summer Lane Wood 13