Rough-Legged Buzzards in Britain in the Winter of 1966/67 by R
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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.