Influxes into Britain of Hen Harriers, Long-eared Owls and Short-eared Owls in winter 1978/79

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1 Influxes into Britain of Hen Harriers, Long-eared Owls and Short-eared Owls in winter 1978/79 D. L. Davenport Si.ATHstaeH. The winter of 1978/79 was the coldest in Britain since 1962/63, and produced outstanding numbers of several species, particularly waterbirds (Chandler 1981). The influx of Hen Harriers Circus cyaneus during the first quarter of 1979, however, was probably the most spectacular event of the winter. This paper documents this influx, together with those of Longeared Asia otus and Short-eared Owls A.flarnmeus, which also occurred in outstanding numbers. (In order to hasten writing and publication, the regions listed in the paper are generally those covered by the individual annual county reports and, therefore, do not necessarily correspond to the areas of the new counties of England, Scotland and Wales.) Hen Harrier In England, the main autumn arrivals of Hen Harriers occur in the southeast from mid October and continue throughout November. By the end of 1978, there were six roosts each of seven or eight individuals in East Anglia and Kent; although these were record numbers, they were by no means unexpected, as a continuing increase has taken place since 1974/75 (see below). The onset of the hard weather, in particular the blizzard of 30th-31st December, and the continuing snowfalls throughout January, produced an unprecedented midwinter influx of Hen Harriers along the length of the east and south coasts of England, especially between North Yorkshire and West Sussex, where numerous roosts were discovered. A much smaller, but equally unusual, midwinter influx of Rough-legged Buzzards Buteo lagopus also occurred on the east coast at this time. The extent of this influx of Hen Harriers is shown in table 1, which gives wintering totals for the principal (mainly coastal) counties and a summarised total for the remaining counties of England. [Brit. Birds 75: ,July 1982] 309

2 310 Hen Harriers, Long-eared Owls and Short-eared Owls in 1978/79 Table 1. Numbers and main roosts of Hen Harriers Circus cyaneus in England, January- March 1979 County areas are generally those covered by the annual county bird reports, and are listed in geographical order County area Total (main roosts) Northumberland Durham Yorkshire (incl. north Humberside) Lincolnshire (incl. south Humberside) Cambridge Huntingdon Norfolk Suffolk Essex Kent East and West Sussex Hampshire Wiltshire Dorset Somerset Devon Cornwall Other county areas (5,7) (4.5,7) (7,14) (4,6,8,8,9,10.13) (5,5,6,9,10,14,18,19) (12) (4,4,4,10,13,20,27) (11) (8) (5) GRAND TOTAL 753 Elsewhere in Britain, there were no reports of unusual numbers of Hen Harriers. In Scotland, for instance, five wintering on the Insh Marshes, Inverness-shire, were described as normal, while three (the same number as in the previous winter) at Loch of Strathbeg, Aberdeen, included one wing-tagged in Orkney. Many wintering in the north of England (including an unprecedented three at Washington, Co. Durham, and an exceptional three at Leighton Moss, Lancashire) probably involved moorland harriers driven to coastal feeding grounds by the severe weather: on the Derbyshire moors, which normally support a winter roost of four to six, there were no records between 31st December and 7th April; although numbers on the 107. Male Hen Harrier Circus cyaneus, Netherlands, February 1976 (Robin Williams)

3 Hen Harriers, Long-eared Owls and Short-eared Owls in 1978/ Female Hen Harrier Circus cyaneus, Hebrides, May 1976 (Dennis Green) Yorkshire moorlands were considered to be above average, as were those elsewhere in Yorkshire and North Humberside. The effects of the hard weather were immediate: by 4th January, there were already 14 roosting at Minsmere, Suffolk, and nearby at the Walberswick roost there was an early peak of 19 by 13th; a secondary roost between these two, at Dunwich, held a maximum often on 12th February. Elsewhere in East Anglia, the largest roosts were of 12 at Tollesbury, Essex, 13 at the main site (locality withheld) in Norfolk, 14 at Wicken Fen, Cambridgeshire, and 18 at Oulton Broad, Suffolk. In Kent, the roost at Stodmarsh increased to 25 by 24th January, with further high counts of 25 on 3rd February, and 27 on 11th comprising seven adult males, three second-winter males, and 17 'ringtails' (females/immatures). A roost on the Thames marshes, at Egypt Bay, Kent, not discovered until 20th February, was frequented by -20 harriers until 19th March; there was evidently a large turnover at this site, which was used by at least 28 different individuals (five adult males, three second-winter males, and 20 ringtails). A further roost, at Walland Marsh, Kent, reached a late peak of 13 on 7th March (this site is of particular interest because, before the recent increase, it was the only documented English roost, having been used by four to six harriers during ). A few other roosts also had their highest numbers in March, presumably owing to returning spring migrants. Information on age and sex was received for two-thirds of the national total of over 750 harriers. This showed that adult males, second-winter males and ringtails occurred in the ratio of 5:1:, although it was apparent that many observers failed to distinguish second-winter males. Long-eared Owl As with the unprecedented influx of Long-eared Owls in 1975/76, the 1978/79 influx was heralded by an outstanding autumn passage, with

4 312 Hen Harriers, Long-eared Owls and Short-eared Owls in 1978/ Long-eared Owl Asio otus, Netherlands, April 1978 (Frits Houtkamp) record numbers on Fair Isle, Shetland, in October. The main arrival was on th- 16th: six on the Isle of May, Fife, and ten on Fair Isle, where up to seven remained until 19th. Fair Isle had another peak of four on 16th November. Farther south there were numerous coastal records of singles in October-November; only one, however, was recorded at Spurn, North Humberside (on 31st October), although up to eight roosted there during 5th-9th December. By December, there were already 50 Long-eared Owls in Kent, half that county's eventual total. Information from other counties suggests that this gives a true indication of the comparative importance of the autumn migration and the subsequent hard weather: the combined effects of these two events produced a winter total second only to that of 1975/76. The 1978/79 influx was confined mainly to Shetland and Orkney, and the east coast from Northumberland to Kent. Table 2 shows the winter

5 Hen Harriers, Long-eared Owls and Short-eared Owls in 1978/ Table 2. Numbers and main roosts of Long-eared Owls Asia otus wintering in Shetland, Orkney and England, 1978/79 County areas are generally those covered by the annual county bird reports, and are listed in geographical order County area Total (main roosts) Shetland Orkney Northumberland Durham Yorkshire (incl. north Humberside) Lincolnshire (incl. south Humberside) Cambridge Huntingdon Norfolk Suffolk Essex Kent London Lancashire Other English Counties (5,14,17) (6,6,20,24) (10,21) (13) (4,4,5,7,14) (4,13,16) (7) (7) (4,5,9,10) (5,6,6,14) (4,5,5,5,7,8,18,32) (4,4,6) (5,6,12) GRAND TOTAL 604 totals for the counties involved, with the largest roosts in brackets, and a summarised total for all other English counties. Short-eared Owl As with the Long-eared, the winter influx of Short-eared Owls in 1978/79 started with an outstanding passage in October. Fair Isle had an early count of on 1st, while on 12th seven arrived on the Skerries, Shetland, 14 on Fair Isle and 25 at the Forties oilfield (176km ENE of Aberdeen). An even larger arrival followed on th October: 30 on Fair Isle, nine on the Isle of May, and 32 along the Aberdeen coast, including 17 between Peterhead and Rattray Head. Although these movements were noted all down the east coast, there was no indication that numbers south of Northumberland were unusual; Spurn, for instance, recorded only up to four between 13th and 22nd October. In the southwest, on the other hand, Cornwall also recorded an unprecedented passage of 50 Short-eared Owls during October-November. During November-December, it finally became evident that virtually all parts of England, both coastal and inland, were affected by an exceptionally large and widespread influx of this species. The effects of the subsequent hard weather served only to augment numbers. Table 3 shows the wintering totals for all English counties, with the largest concentrations in brackets. There was no indication of unusual numbers elsewhere (in Shetland, there were no records at all of Short-eared Owls in the first quarter of 1979). Discussion It is now evident, in retrospect, that numbers of Hen Harriers wintering in southeast England have increased steadily over the last 20 years. Recently, this increase has accelerated, and numbers have trebled between 1975 and In Kent, for instance, compared with a normal wintering population

6 314 Hen Harriers, Long-eared Owls and Short-eared Owls in 1978/ Short-eared Owl Asioflammeus, Netherlands, February 1976 (Frits Houtkamp) of about 12 in the early 1970s, there were 18 in the winter of 1977/78 and 38 in 1979/80. An interesting aspect of this sudden increase has been the inevitable discovery of numerous winter roosts. In Norfolk, the main roost has held four or more harriers since as long ago as 1968/69, and another roost of five was found in 1974/75; in 1975/76, one of six was present in Breckland, an area where no significant roosts were reported in 1978/79. In other counties, the first roosts of four or more were reported in Lincolnshire in the 1974/75 winter, in Kent (apart from , see above) and in Yorkshire in 1976/77, and in Suffolk and in Cambridgeshire in 1977/78, although such gatherings could not be considered widespread until the hard winter of 1978/79, when there were 33 major roosts totalling 311 harriers along the south and east coasts of England. The counties of Kent and Suffolk have since held five regular roosts apiece, each totalling 30 individuals, while Norfolk had seven totalling 44 in 1979/80. The parallel increase of the much scarcer Rough-legged Buzzard in winter on the east coast of England has to some extent been concealed by its large autumn irruptions, the most recent in 1966, 1973 and 1974 (Scott 1968, 1978). Numbers of Long-eared Owls wintering on the east coast of England have also increased significantly in recent years: in Kent, following the

7 Hen Harriers, Long-eared Owls and Short-eared Owls in 1978/79 3 Table S. Numbers and main roosts of Short-eared Owls Asmflammeus wintering in England, 1978/79 Areas are listed alphabetically and, apart from the four West Midland counties, are generally those covered by the annual bird reports Area Total (main roosts) Area Total (main roosts) Avon Bedfordshire Berkshire Buckinghamshire Cambridge Cheshire Cornwall Cumbria Derbyshire Devon Dorset Durham Essex Gloucester Hampshire Herefordshire Hertfordshire Huntingdon Kent Lancashire Leicestershire (10,10,12,20) (20) (16) (8) (11) (8,12) (8,10,20,20) (8,8,9,14) (9) (8,8,12) (9,9,12) (8) Lincolnshire (incl. south Humberside) London Norfolk 50 Northants 50 Northumberland 60 Nottinghamshire 55 Oxfordshire 55 Shropshire 10 Somerset 42 Staffordshire Suffolk 40 Surrey 25 Sussex (East & West) 30 Warwickshire 25 West Midlands 10 Wiltshire 28 Worcestershire 6 Yorkshire (incl. north Humberside) 70 (8,10) (11) (9) (9) (20) (12) (9,20) (12) (8,10) GRAND TOTAL 1,549 record total of 170 in 1976, there were 72 in 1977 and 54 in 1978, numbers which in any other context would have been considered exceptional, while in early 1979 there was a total of 104. Most of the Kentish roosts are situated in, or adjacent to, large roosts of finches (Fringillidae) and sparrows Passer, although the owls' main food apparently consists of voles (Microtinae). It is interesting to note that the Long-eared Owl is now occurring in a pattern similar to that of the Rough-legged Buzzard: occasional large autumn influxes, as in 1975 and 1978, set against a background of a sustained increase. It may well be that the failure of the Hen Harrier to occur in large autumn irruptions has kept this interesting species out of the limelight, and certainly its increase as a winter visitor is difficult to monitor, until the population builds up to such a level that the main roosts are unavoidably discovered. The immediate origin of Hen Harriers wintering in southeast England is presumed to be the Netherlands, where breeding numbers have greatly increased in recent years: from -20 pairs in 1964, and pairs in 1970, to pairs in 1977 (Schipper 1979). There has also been a much larger increase in the wintering population there, which cannot be explained entirely by the breeding numbers (G.J. Oreel in litt.). Of particular interest are reports of a strong southerly movement of Hen Harriers in the Netherlands during the first week of January 1979, including seven to 11 per hour at three coastal sites on 4th (Verslag van de Club van Zeetrekwaarnemers 16:24). There was another large influx of Hen Harriers into southeast England in the severe winter of 1981/82. In Kent, where the five main roosts each held

8 316 Hen Harriers, Long-eared Owls and Short-eared Owls in 1978/79 nine to 14 birds, the figures suggest a population as high as 70% of that of the 1978/79 influx. Acknowledgments The original data for this paper were collected by I. Dawson and J. N, Hollyer, after requests for information were made nationally, while much additional material has been taken from the published county reports. The following county recorders and individual observers supplied information necessary for the compilation of the tables, or sent details on individual Hen Harrier roosts:j. S. Armitage, K. Atkin, D.J. Barker, R. Berry, B. Bishop, M. Blackburn, Dr W. R. P. Bourne, P. Clarke, B. Cobbold, C.J. Coe,J. Cudworth, C. Davies, N. Davies, M. K. Dennis, A. Dobbs, D. A. Dorling, G. Ekins, M. Everett, R. Forrester, R. Frost, B. Galloway, A. Grieve, E. Griffiths, J. P. Guest, G. R. Harrison, W. G. Harvey, R. Heath, P. Hopkin, J. Howard, I. W.Jennings, R. Key, B. King, C. A. E. Kirtland, R. Leavett, S. E. Linsell, J. A. McGeoch, G. E. Manser,J. R. Mather, D. R. Moore, P.J. Mountford, P.J. Oliver, A. Paine, B. P. Pickess, A. Pickup.J. Sanders, M.J. Seago, S. Shepherd, N. Sills, F. Solly, M. Stott, M.J. Tickner, R. Turner, B. Unwin, j. Wheatley, J. Wilson. Summary An unprecedented midwinter influx of Hen Harriers Circus cyaneus took place on the south and east coasts of England in the severe weather ofjanuary This influx is presumed to have come from the Netherlands. Over 750 individuals were wintering in England during the first quarter of 1979: these included 33 roosts totalling 311 harriers, with the largest roost containing a maximum of 27. The age:sex ratios, where given, comprised 5 adult males: 1 secondwinter male: females/immatures. This influx occurred during a period of continuing increase in the wintering population of Hen Harriers in southeast England, where numbers have trebled during The habit of forming regular winter roosts, virtually unrecorded in England before 1974/75, has now become a common feature of this species' behaviour. Numbers of Long-eared Asio otus and Short-eared Owls A.flammeus were also exceptional in 1978/79. About half the Long-eared and probably a much higher proportion of the Shorteared, arrived during an exceptional autumn passage in the last quarter of 1978, while the severe weather ofjanuary 1979 produced a fresh influx to augment these numbers. The total of Long-eared Owls was second only to the unprecedented influx during the autumn and winter of 1975/76. References CHANDLER, R, J Influxes into Britain and Ireland of Red-necked Grebes and other waterbirds during winter 1978/79. Brit. Birds 74: SCHIPPER, W.J. A In TEIXEIRA, R. M. Atlas van de Nederlandse Broedvogels. 's-graveland. SCOTT, R. E Rough-legged Buzzards in Britain in the winter of 1966/67. Brit. Birds 61: Rough-legged Buzzards in Britain in 1973/74 and 1974/75. Brit. Birds 71: D. L. Davenport, 68 First Avenue, Gillingham, Kent