Rough-legged Buzzards in Britain in the winter of 1966/67 By R. E. Scoff

Dungeness Bird Observatory

INTRODUCTION The Handbook of British Birds (1938-41) describes the status of the Rough-legged Buzzard Buteo lagopus In Great Britain as a winter visitor which occurs in most years in the northern isles and on the east coast of Scotland and England as far south as Suffolk, adding that it is rarer in south-east England and especially scarce in the west. It is therefore of some interest that exceptional numbers were reported in the autumn and winter of 1966/67, particularly in the south-east. A request for information was published (Brit, Birds, 60: 139-140) and letters were sent to county and regional recorders and editors asking for their assistance in collecting information relating to the influx. This paper analyses the data received and also presents the results of enquiries about the status of the species in northern Europe in 1966. The Handbook lists eight winters when the Rough-legged Buzzard is known to have been particularly numerous in Britain, intervals between these influxes ranging from five to 19 years with an average of eleven, the last as far back as 1915/16. Since then there have been minor influxes at long intervals (for example, in 1937/38), but the efficiency and number of observers now in contrast to those earlier years make comparison difficult. Certainly there was nothing compar­ able to 1966-67 in the preceding decade, as is shown by the records obtained by Dr. J. T. R, Sharrock (in lift.) as part of a ten-year analysis, covering 1958-67, of the status in Britain and Ireland of this and a number of other regular but scarce visitors.

AUTUMN 1966 The first Rough-legged Buzzard to be recorded in Britain in the autumn of 1966 was seen over Ancaster, Lincolnshire, on 1st October. There were then records in Cornwall, Norfolk and Yorkshire during the 6th-8th and others in Huntingdonshire and Northumberland by the nth, in Kent by the 15th and in Pembrokeshire by the 16th. From the 19th onwards they were quite widely distributed, with the main influx in south-east England taking place during the 27th-29th, although by this time considerable numbers were already in the country and it was becoming difficult to distinguish new arrivals from those which had wandered from other areas where they had already been recorded. By the end of October Rough-legged Buzzards had been seen in 20 counties (fig. 1). The bulk of the records were con-

449 BRITISH BIRDS

FIG. I. October 1966 (also Scilly, FIG. 2. November 1966 (also Scilly Orkney and Shetland) and Shetland) Rough-legged Buzzards Buteo lagopus in Britain during the winter of 1966/67, the counties involved in the periods shown being marked in black {drawn by P. J. Grant) centrated on the east coast from Northumberland southwards; there •were rather fewer reports from eastern Scotland, although most of the individuals concerned there had appeared slightly earlier than the the main arrivals in England (the first in Shetland on 18th October). Occurrences in Cornwall on 6th October and in Pembrokeshire on the 16th suggested a small arrival in the south-west, as did one in the Isles of Scilly on 28th October, the last coinciding with the main influx in the south-east. Single observations in Staffordshire on 23rd October, in Wiltshire on the 28th and in Worcestershire on the 29th possibly lelated to individuals which were moving on after reaching Britain earlier in the month. There was a clear reduction in the number of counties which lecorded Rough-legged Buzzards in November (fig. 2) and many of the birds which subsequendy wintered had already settled down by the beginning of that month. It is probable that little or no further immigration took place during November (although it would have been impossible to distinguish a small arrival in the south-east) and, apart from those in Shetland and Angus/Kincardine, the birds in east coast counties were confined to die area south of the Humber. Never-

450 ROUGH-LEGGED BUZZARDS IN WINTER 1966/67

FIG. 3. December-February (also FIG. 4. True wintering birds (also Shetland) Shetland) Rough-legged Buzzards Buteo lagopus in Britain during the winter of 1966/67, the counties involved in the periods shown being marked in black {drawn by P. J. Grant)

theless, some movement westwards in this month was shown by records in Staffordshire, Lancashire and Anglesey.

WINTER 1966/67 Fig. 3 shows the counties in which Rough-legged Buzzards were recorded during the winter months from December to February, regardless of whether they stayed for any length of time. Fig. 4, on the other hand, is confined to individuals that remained in one area throughout these months, or at least for periods of over four weeks. It will be noted that the casual records in fig. 3 extended the winter area only slightly west and south. The minimum number of Rough- legged Buzzards which actually wintered was 5 7, as follows: Wiltshire 1 Oxford/Buckingham 1 Huntingdonshire 3 Hampshire 1 Suffolk 14 Angus/Kincardine 2 Sussex 4 Norfolk 11 Ross 1 Kent 12 Cambridgeshire 1 Shetland 6 The records also suggest at least a further ten, as follows: Somerset 1 Dorset 1 Shropshire 1 Midlothian 1 Wiltshire 3 Essex 2 Lincolnshire 1 451 BRITISH BIRDS Thus we have a likely minimum of 67 individuals present throughout the winter, but even this may be well below the true figure as observations from Scottish, Welsh and western counties of England are possibly not complete. It will be noted that the great majority of the wintering birds were in Suffolk, Kent and Norfolk, these three counties between them accounting for 37 of the records. Of these 37, over half were in the Brecks and on the Suffolk coast between Orford and Benacre, five being seen together at Walberswick on several occasions. Six more were on the Isle of Sheppey, Kent, while the remainder in these counties favoured similar habitats in Romney Marsh, the east and north Kent marshes, the Broads, the north Norfolk coast and the Wash.

SPRING 1967 It is very difficult to distinguish records relating to a return passage in spring as many of the Rough-legged Buzzards which wintered remained until late March or even early April. Figs. 5 and 6 show the counties which recorded these birds in March and April. It appears that they departed first from the central and southern counties, known winterers last being seen in Hampshire on 26th February, in Oxford/Buckingham

FIG. 5. March 1967 (also Shetland) FIG. 6. April 1967 (also Shetland) Rough-legged Buzzards Buteo lagopus in Britain during the -winter of 1966/67, the counties involved in the periods shown being marked in black {drawn by P. J. Grant) 452 ROUGH-LEGGED BUZZARDS IN WINTER 1966/67 on 15th March, in Wiltshire on 19th March and in Sussex on 28th March. They had left Huntingdonshire by early April, but were still being recorded regularly in Kent, Suffolk and Norfolk in the second half of that month. Two in Somerset on 4th April and one in Dunbarton on the 22nd may possibly have been on passage or equally may have been previously overlooked winterers which were starting to wander over greater areas. The following records seem likely to have referred to spring passage: Pegsdon, Bedfordshire, I2th-24th March Dunbarton, 22nd April Ruabon, Denbighshire, 17th March Cley, Norfolk, 24th April Spurn, Yorkshire, 2nd-30th April Unst, Shetland, 9th May Wellington, Somerset, 4th April (two) Wareham, Dorset, nth and 13th May Dungeness, Kent, 13th April (two) Haldon, Devon, 28th-2C)th May EUROPEAN BREEDING POPULATIONS 1966 All the data obtained on the comparative size and breeding success of Rough-legged Buzzard populations in 1966 came from northern Fenno-Scandia. Olavi Hilden (in litt.) provided information from five areas of Finland. (1) At Karigasniemi the population was very small and obviously to a great extent non-breeding; during June and July soaring birds were seen only twice, whereas in peak years one expects to see them every day. (2) At Kevo the population was low; two of three young disappeared from the one nest found. (3) At Kilpisjarvi the population was almost nil; in early July only one bird was observed in an area where four or five pairs normally breed. (4) In western Lapland and northern Norway not a single Rough-legged Buzzard was seen during a car journey in mid-June, whereas in normal years numbers are recorded on this route. (5) By way of contrast, at Kittila, further south in Lapland, the population was high and breeding success fairly good. At Karigasniemi, Kevo and Kilpisjarvi it was also noted that there was an almost complete lack of small mammals and this was considered to be the reason for the absence of the predators from these and other areas. A similar picture emerged from Finnmark where Rodney Gayer (in litt.) recorded only one breeding pair in the entire area of Porsan- gerfjord (with another pair in Varangerfjord); apparently no young were reared there. In 1965, by comparison, Rough-legged Buzzards were described as 'abundant' in this part with a pair inhabiting almost every suitable hillock, and in 1967 some twelve pairs were nesting in a 40-mile length of the western shore of Porsangerfjord. Further, the rodent population had reached a peak in this part of Finnmark in 1965 and then collapsed, with the result that there was an almost total lack of small mammal activity. As in Finland, it appeared that predators were more abundant further south in Norway, this being illustrated by the commonness of Long-tailed Skuas Stercorarius longicaudus near Sulitjelma at latitude 6y°N.

453 BRITISH BIRDS From the limited information available, it appears that food shortage on the northern breeding grounds caused the Rough-legged Buzzard populations to shift further south and west in 1966. The movement to Britain was probably direct from these areas, for, apart from eastern Sweden where Rough-legged Buzzards on passage are possibly of more eastern origin, the nearer Continental countries apparently experienced no marked increase or decrease in passage numbers and arrivals coincided with that in south-east England, as is shown in the next section.

CONTINENTAL PASSAGE AND WINTERING 1966/67 Requests for information on the relative abundance of Rough-legged Buzzards in the autumn of 1966 and the subsequent winter were sent to ornithologists in a number of Continental countries. There was a lack of comparative data, unfortunately, but the general impression from most sources was that events in 1966/67 were not strikingly diff­ erent from normal in these other countries, so that the species did not attract attention. Some of the information received is summarised below: Finland Passage was either normal or less than average, but passage records are never numerous (O. Hilden). Sweden At Ottenby, on the east coast, a heavy migration was recorded from 23rd September, with a peak of 192 on 12th October and 41 next day, then another small peak on 24th-26th October including 44 on the 25 th. Passage apparently ended there on 28th October (possibly coincidental, but this was the time of the main influx into south-eastern England). These figures may be compared with only 'very small numbers' in 1965. In contrast, at Oxelasund, south of Stockholm, passage was light compared with the preceding two years (only 32, against 80 in 1965 and 100 in 1964). There was apparently little difference in the wintering population within the country (R. Edberg). Netherlands Passage along the North Sea coast was probably less than normal, although the first five appeared on 29th October at the time of the arrival in south­ east England. Four or five wintered on the island of Terschelling (M. J. Tekke). Belgium One or two are known to have wintered and one ringed on 2nd November was found dead in late March. Little evidence of passage and nothing unusual (R. F. Verheyen). France The only passage observations came from Cap Gris Nez where one flew south on 26th October and another was seen on the 27th. These records immedi­ ately preceded the arrival in south-east England (A. Gibbs).

BEHAVIOUR, FOOD AND AGE Very few observers provided information beyond dates, localities and numbers. Most frequently mentioned otherwise was mobbing by other birds: Carrion Crow Corpus corone topped the list with three reports, followed by Short-eared Owl Asio flammeus with two, and Marsh Harrier Circus aeruginosas, Kestrel Fa/co tinnunculus, Common Gull Larus canus, Black-headed Gull L. ridibundus, Raven Corpus corax, 454 ROUGH-LEGGED BUZZARDS IN WINTER 1966/67 Rook C. frugilegus and Jackdaw C. monedula with one each. Only two observations referred to roosting: in one case, two Rough-legged Buz­ zards made regular use of a plantation of Scots pine Pinus sylvestris throughout the winter; and in the other, one 'probably' spent the night in a larch Larix decidua. Of four reports which mentioned food, three referred to regular feeding on Rabbits Oryctolagus cuniculus (in two of these cases an out­ break of myxomatosis in the local Rabbit populations had resulted in many corpses in the areas concerned). The last report involved a Rough-legged Buzzard being flushed from a dead Woodpigeon Columba palumbus (cause of death unknown). Observers who attempted to age the Rough-legged Buzzards they saw recorded only one adult against five in immature plumage.

ACKNOWLEDGEMENTS The preparation of this short paper would not have been possible without the co-operation of the many observers, recorders and editors who so willingly sat down and replied to my requests and letters. I should like to express my grateful thanks to them all, though they are unfortunately too many to mention by name. The ornithologists who assisted with the collection of the foreign data are mostly named in the text and I am equally grateful to them, including Anders Enemar and Professor Dr. K. H. Voous who provided further contacts. Dr. J. T. R. Sharrock helped in several ways and I. J. Ferguson-Lees was of great assistance in getting the enquiry off the ground and producing the initial list of contacts. Finally, but very far from least, P. J. Grant kindly drew the maps.

SUMMARY An influx of Rough-legged Buzzards Buteo lagopus into Britain in the winter of 1966/67 involved more records than in any other winter in at least the preceding decade and possibly 30 or even 50 years. The first was recorded on 1st October and the main influx took place in south-east England during 27th-29th October (the coincidence of the dates of a small number of records in the north and south­ west in mid-October suggested a separate arrival in those areas then). At least 57 individuals are known to have wintered in Britain, the majority of them in the south-east, and a further ten probably did so. Most had departed by late March, but a few were recorded in April and the first half of May, and one as late as the end of May in Devon. Details are given of somewhat limited Continental observations on the breeding and migration of this species in 1966 compared with previous years. From these it appears that the northern populations were reduced in size and generally unsuccess­ ful in 1966, and that the centre of the Fenno-Scandian breeding range had shifted south and west. The chief reason for this was considered to be the scarcity of small mammals in northern latitudes in 1966. Continental observations on passage movements suggested that numbers in the autumn of 1966 were generally little different from average. Brief notes at the end summarise scanty British observations on mobbing by other species and on roosting and food.

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