Seabird movements along the east coast of England D. I. M. Wallace and W. R. P. Bourne

t has been known for over a century that large movements of — Iincluding scarce species—may occur at intervals, at any time of year, along the east coast of Britain following the onset of northwest to east winds (Nelson et al. 1907, Temperley 1951). Some of the birds fly south, and may converge along the coasts of Lincolnshire and Norfolk on the Wash {Cambridge Bird Report 1954 onwards; Bourne 1976a), or the Thames estuary (Davenport 1971), where in autumn the skuas Stercorarius, terns Sterna and Kittiwakes Rissa tridactyla may continue overland, while others, such as the Sooty Shearwater Puffinus griseus, may continue through the Strait of Dover (Oliver 1971, Oliver & Davenport 1972). More commonly, they fly north until the coastline turns west in the Grampian region, where some may follow it and a few continue southwest overland down the Great Glen in the autumn (personal observation by WRPB), but many go out to sea between northwest and north, and may eventually reach the Atlantic around north Orkney. They appear to avoid the Pentland Firth (Lea & Bourne 1975). The movement has been studied where it starts to leave the land at Rattray Head by Elkins & Williams (1970, 1972), who found that, in addition to large numbers of the main resident species, such as Fulmars Fulmarus glacialis, Gannets Sula bassana, Kittiwakes and auks (Alcidae), migratory tubenoses and skuas sometimes appear at appropriate seasons. When large numbers of the latter two groups were reported all down the east coast after the hot summer of 1976, we decided that they required further investigation and appealed for information (Brit. Birds 70: 40). A subsequent increase in sea-watching, combined with studies of the birds occurring at oil installations (Bourne et al. 1979), indicated that, while 1976 was indeed a good year for the occurrence of scarce species, it was by no means unique. Large movements occurred again in the autumn of 1978 and spring of 1979, and investigations then have helped elucidate their nature.

Geographical situation, and movements of common species Current information on the marine environment is summarised in Scottish Fishery Bulletin 45, and its application to ornithology is discussed by Bourne (1976b, 1978, and in Cramp et al. 1974) and Joiris (1978). A current of

[Brit. Birds 74:417-426, October 1981] 417 418 movements along the east coast of England Atlantic water with a rich and varied oceanic plankton exploited by young fish hatched off the north of Scotland enters the area around Shetland and flows down the east coast of Britain. There, it is mixed by tidal currents with fresh water from the rivers and cool bottom water containing nutrient salts which sustain a further growth of plankton. The growing fish congregate in this area, which supports a vast breeding population of seabirds (Cramp et al. 1974), and in winter provides a refuge from Atlantic gales for northern winter visitors. As the water shoals south of Head, Humber- side, it becomes more uniformly mixed, and the larger marine organisms are replaced by bacteria which help to make the water turbid. Thus, elsewhere in the North Sea there is less food for birds and the diving species cannot find it, and they are replaced by smaller numbers of aerial gulls and terns feeding at the surface. During 1978-79, co-ordinated observations along the east coast of Scotland, at the oil platforms on the Forties Field in the central North Sea (Bourne et al. 1979), and from helicopters flying between the two, together with RAF distant early warning radar covering the area, provided an insight into the seabird movements. The birds feed when dispersed at sea, gathering in flocks behind trawlers and over the fish-shoals, which are particularly numerous along the front which occurs in summer a few kilometres offshore between the well-mixed coastal water and the stratified water farther out; it is sometimes marked by the formation of a line of scum. They appear to have much spare time, which they spend resting in groups on the water, along the shore, around the oil installations, and (once they have completed their moult) in visiting the colonies, which are occupied in fine weather by some species such as Fulmars, Herring Gulls Lams argentatus and Guillemots Una aalge for much of the year (Greenwood 1972). Northward movements are sometimes distinguishable at sea with warm south winds on the west side of the high-pressure systems in the spring, but are seldom marked. Southward ones are more prominent, with cold north winds on the western side of low-pressure systems at most seasons, and become large at times in the late autumn. North winds persisted for several weeks during the spring of 1979, and on radar films the feeding seabirds, which usually mill about at random out at sea, could sometimes be seen beginning to drift slowly southward as the wind rose. Some of these birds could be seen from the shore, but the movement soon became incon• spicuous there because the birds drifting south out at sea were greatly outnumbered locally by a concentrated return movement north up the coast, presumably because the wind is weaker there. As the wind fell, they started to return north out at sea as well, and the coasting movement died away. A further example of the effect of drift on seabird movements, of the type probably responsible for many large east coast influxes, occurred when a strongly-developed front moved north over the area on 9th December 1978. During a helicopter trip out to the oilfield in a violent easterly gale (as the front passed during the morning), those birds which could be seen appeared to be drifting slowly west low over the water with the wind. Then, as the wind fell during the afternoon, Alan Morley saw an unprece- Seabird movements along the east coast oj England 419 dented return movement, of 1,000 Kittiwakes with some Common Gulls Lams cams and auks, east, past the oilfield, with smaller numbers again next day. Comparatively few birds accumulated along the coast at this time, as the gale moved on rapidly, but, with sustained east winds, large numbers accumulate offshore and head into the wind along the coast. Status of scarcer species The long, hot summer of 1976 was accompanied by the appearance of numbers of Manx Shearwaters Pujftnus puffinus off North Humberside. As the warm weather gave way to north winds, mist and rain in the third week of August, modern records for the numbers of Great P. gravis and Cory's Shearwaters Calonectris diomedea, and Pomarine Stercorarius pomarinus and Long-tailed Skuas S. longicaudus, were broken. Later, the record for Sooty Shearwaters was also broken and that for Pomarine Skuas was matched in 1978. It also became clear from a scrutiny of the older literature that at least the skua observations were far from unprecedented, although there appears to have been an increase in the number of shearwaters recorded in recent decades, possibly owing to more effective observation. Seabird movements, including a large proportion of the scarce skuas, were noticed on the east coast in autumn at least as early as 1867 (Zoologist (1867): 1008-1014). They were prominent again and received a great deal of attention in the early years of the enquiry into migration at coastal lights. Numbers of terns and Arctic Skuas S. parasiticus were attracted to Tees Bay by small fish in September 1879, and 40-50 skuas were shot. Then 'thousands' of Pomarine Skuas, with smaller numbers of the other species, appeared there from the east about one hour after the onset of a north- veering-to-northeast gale and heavy rain on the morning of 14th October 1879, and some flew north up the coast while others continued inland. They were very tame, and over 150 were shot. There were still considerable numbers next day and, when the wind rose again, on 17th, and they were seen at least as far south as Norfolk. Similar movements on a smaller scale were noticed on the coast again on 28th October 1880 (Zoologist (1880): 8-19, 511) and on 30th November 1911 (Nelson 1911). Manx and Sooty Shearwaters were first noticed to reach hundreds off the Isle of May in late September 1959 (Watson 1959). The old records confirm the impression from modern observations that numbers of scarce migrants may accumulate offshore in some autumns, notably those when there are many shoaling fish, and that the birds are then liable to be brought inshore by north to east winds. The following summary shows the status of the scarcer species. Fulmar Fulmarus glacialis Coasting movements of pale birds reaching 3,000 to 5,000 per hour occur from Scotland to south of the Humber at intervals throughout the year. They are commonest from early March to early May and from early August to mid September, with a drop then as the young fledge and their parents go to sea to moult. The movements are sometimes, but not always, associated with those 420 Seabird movements along the east coast oj England of the shearwaters. Grey Fulmars with dark underwings, which are very rare in the British breeding population, are now being recorded increasingly frequently at all seasons, occasionally forming up to 8% of those passing Flamborough Head. On 17th December 1978, there were 225 normal Fulmars, 2,225 pale grey ones, four darker and one very dark individual there; presumably, they belonged to the small, dark northern populations also wrecked all around the North Sea in the spring of 1962 (Pashby & Cudworth 1969).

Cory's Shearwater Calonectris diomedea This species was recorded on the east coast only erratically until 1975, though perhaps it was con• fused with the Great Shearwater at times. In 1976, at least 33 were reported between Sutherland and Norfolk between 21st August and 10th October (Brit. Birds 70: 412-413; 71: 488). The northerly distribution of the records suggests that in this hot summer they spread unusually far north in the Atlantic and arrived around the north of Scotland; the last one was returning west around Duncansby Head. Another ten appeared in 1977, but were all preceded by or associated with occurrences along the south coast (Brit. Birds 71: 488; 72: 509), and there was only one Scottish record, of two off East Lothian on 18th April, which suggests that they arrived through the English Channel. Eleven occurred on the east coast in 1978, and 19 in parties of up to eight in 1979, with a distribution which suggests a joint northern and southern origin, but mainly the latter (Brit. Birds 72: 509; 73: 493). They apparently now occur regularly in small numbers from April to early October.

Great Shearwater Puffinus gravis Although it has not been recorded in the North Sea in the thousands that regularly appear in the southwest approaches, and even the great invasion up the west coast of 1965 appears to have stopped short around Fair Isle (Newell 1968), this sturdy species has been reported along the northeast coast at intervals for over a century, and we doubt whether the recent increase in reports represents any long-term change in status. In 1976, the numbers seen off north and east Scotland were exceptional, with at least 66 between 19th August and 2nd October. Of these, 37 passed Tarbat Ness, Highland, on 29th August, which suggests that they were accumulating in the Moray Firth (Scot. Birds 10: 81). They were reported in unusual numbers off northeast England again in 1978, when at least 30 passed Flamborough Head between 6th August and 30th September, with 13 on 20th September (per P. A. Lassey). Sooty Shearwater Puffinus griseus This species, which regularly comes closer inshore than the other large shearwaters, occurs off the east coast annually in the late summer, and is frequently recorded coasting as far south as the £ Humber, usually flying north, which may explain the appearance of an accumulation of 500 off the ''"'■ Isle of May on 25th September 1959 (Watson 1959). The unprecedented total of 1,000 with the Great Shearwaters off Tarbat Ness on 29th August 1976 has since been matched once and approached several times at several stations south to Flamborough Head, where over 5,000 bird-days were recorded in 1978 (per P. A. Lassey). They are seen regularly from July into October, with some until mid winter, but are exceptional in spring. Most occur with onshore winds, which are commonly associated with a poor visibility on this coast. Many may leave around the north of Scotland, but many others leave through the Strait of Dover (Oliver 1971), where 1,400 were seen flying southwest off Cap Gris Nez on 1st and 2nd October 1977 (P. S. Redman in lilt.). Seabird movements along the east coast of England 421 Manx Shearwater Puffinus puffinus This species has certainly also occurred regularly off eastern Britain south to the Humber from March to November for at least 20 years (Watson -J 1959), with occasional individuals in the winter. "<^ AJLZ& Most occur in a belt just offshore, and they tend to —-- ~^Ul '"- ~ ~~- I--~—-----' gather off the mouths of inlets such as the Moray " ~ ~ — Firth and Firth of Forth. Reports that it is 'rare', or at best 'not infrequent' in the North Sea (Cramp & Simmons 1977) refer to the far south and east coasts. Coasting movements may reach 100 per hour and total up to 1,160 birds, with one evening movement of 700 ofTFlamborough Head in July 1976. They do not, however, obey the regular pattern seen with those commuting to and from the west coast breeding colonies: it seems likely that they involve immature non-breeders. Individuals resembling the Mediterranean forms regularly appear among them; a number of specimens collected in the past all belonged to the Balearic race P. p. mauretanicus (Witherby 1921), and the Levantine race P. p.yelkouan has not yet been proved to occur.

Little Shearwater Puffinus assimilis Between 1975 and 1980, about 25 'small, fluttering shearwaters' have been reported along the east coast from Grampian to Norfolk. The 12 records that have been accepted all come from Flam- borough Head as the result of increasingly experi• enced and intensive sea-watching (Brit. Birds 70: 413; 71: 489; 73: 493) and have occurred between June and early October. It seems likely that they arrive with the Cory's Shearwaters, which have a rather similar distribution elsewhere in the North Atlantic, except that the Little Shearwater tends to breed early in the year and then disperse northwards (Bourne 1967). Small black-and-white shearwaters clearly deserve more attention.

Bulwer's Petrel Bulweria bulwerii This species has not been certainly recorded recently, but three old records, at Tanfield, North Yorkshire, on 8th May 1837, from Scarborough, North Yorkshire, in 1849, and at Scalby Mills near Scarborough on 28th February 1908 (Bourne 1967), fit in with the recent occurrence of other subtropical species such as Cory's and Little Shearwaters.

Storm Hydrobates pelagicus and Leach's Petrels Oceanodroma leucorhoa In spite of the recent increase in sea-watching, *. which often reveals their presence off the west coast, the smaller petrels are seldom seen in the ._ ; -V. east. The first species occurred in dozens in wrecks —-._".". of a variety of seabirds all down the east coast with , northerly gales in early October in 1867 and 1880 (Zoologist (\867): 1008-1014; (1880):511),andhas ~? ,_ recently been found to occur at night in " ^'"~ summer in the Forth (Maguire«ia/. 1980), where it has bred in the past. It is still seldom seen by day either from the coast or at sea south of Grampian. The second, which is more highly pelagic, is rare everywhere, with its periodic wrecks starting in the west. While it may seem amazing that more Little Shearwaters than Leach's Petrels have now been seen from Flamborough Head, Dr J. T. R. Sharrock (in litt.) has pointed out that this is also true of Cape Clear Island, Co. Cork. 422 Seabird movements along the east coast oj England Great Skua Stercorarius skua This species is normally present in small numbers around the offshore oil installations and elsewhere at sea in summer. Some also occur in the seabird coasting movements, but they are not as sociable as their congeners and there are seldom more than a hundred in a day off any station. They now sometimes occur in winter. Pomarine Skua Stercorarius pomarinus Long before it was found to occur in numbers along the south and west coasts in spring (Davenport 1975), this was traditionally the dominant species in large late-autumn skua . movements along the east coast (Nelson el at. 1907; Nelson 1911; Temperley 1951). There have been few records in recent years to compare with those in the last century already discussed, though they were obvious all down the east coast and passing through the Strait of Dover again in 1970 (Oliver & Davenport 1972). In 1976, 430 were reported off eastern Scotland and 290 off Yorkshire and North Humberside (Scot. Birds 70: 98; Mather 1972), twice the established average at the time, and they again appeared prominently in 1978. Most were seen in September and early October, somewhat later than the main Arctic Skua passage, but spring and summer records now also occur annually, forming a clear extension of the larger English Channel passage up the east coast (Davenport 1975). It remains rare in winter. Arctic Skua Stercorarius parasiticus This species regularly accompanies the large flocks of terns which feed off the east coast in early autumn, when it is the commonest skua, and it can also be seen moving on overland from the Wash and the Thames Estuary (Davenport 1971; Bourne 1976a). It has apparently never been so numerous as the Pomarine Skua in the big, occasional, late-autumn passages; it was reported to be only one-fiftieth as common as the Pomarine Skua in that of 14th October 1879 (Zoologist (1880): 18-19). Apparently, there were no more Arctic Skuas than usual in the skua passages of the autumns of 1976 and 1978. Long-tailed Skua Stercorarius longicaudus This delightful bird normally stays far out to sea on migration (Bourne & Harris 1979), and has apparently always been scarce inshore, so that, for example, it was represented by only five in Tees Bay and 43 in total in the great influx of October 1879 (Zoologist (1880): 18-19; Bannerman 1963). The small number of reports may be due partly to caution over identification, since some have lost their characteristic long tail feathers by the time they migrate. This factor also hinders definition of its distribution in winter, when it has been recorded most commonly off southern South America (Murphy 1936), though it seems to occur widely in the southern oceans in the off-season. All past totals for the east coast have now been surpassed by 103 records accepted between 21st July and 18th October 1976, with over half of them coming from the seawatching station on Flamborough Head (Brit. Birds 70: 424-445; 71: 505; 72: 526). The 1976 total was about seven times the annual number accepted as normal at the time (Sharrock 1974). In the next three years, however, 40, 48 and at least 27 were recorded annually (Brit. Birds as above; 73: 510-511), which suggests that, in fact, the 1976 total was only twice or thrice as large as usual. The species is rare off the east coast in spring and unknown in winter. Seabird movements along the east coast of England 423 Sabine's Gull Larus sabini Only nine years ago, this species, which breeds in the Arctic and winters off South Africa, could still be described as a 'scarce but regular passage or drifted migrant, ten or more annually' (BOU 1971), and there was thought to be a southwest bias to the records similar to that found with the rarer tubenoses. While there are still less than ten records annually from the east coast of Scotland, over 20 a year are now expected from the east coast of England, where it has been recorded in all months. At Flamborough Head—an exceptional station projecting 10 km out to sea—the annual total rose from 25 in 1976 and 1977 to 27 in 1978 and at least 33 in 1979, and no less than 28 occurred in movements of up to seven individuals, with a high incidence of on-shore winds between December and March in winter 1978/79. In view of the number of specimens taken between Flamborough and in the last century (Nelson et at. 1907), it is not clear that this is necessarily a new phenomenon.

Conclusions For a long time, it was not appreciated that the northeast coast of Britain is one of the great seabird nurseries of the North Atlantic, frequented by astonishing numbers of birds throughout the year. The feeding-grounds which support these birds appear to attract and hold for a time a good many other wandering individuals, which can also be seen in the coasting movements associated with changes in the weather (or, to be precise, first participating in and then compensating for the drift with the wind which is liable to occur then). For geographical reasons, these effects are most marked with the north winds which drift birds from the Shetland area into the North Sea in the late summer and autumn, when they bring shear• waters filtering into the area around the north of Scotland from the Atlantic and cause migrating skuas and Sabine's Gulls to enter the North Sea, where these species are seldom seen in the spring. Until recently, most of the records dated from the last century, when this coast was known to be a collector's paradise and received special attention during the early phases of the enquiry into bird migration at the coastal lights during the 1870s and 1880s. It is rather puzzling why there have been so few comparable recent observations. It may be partly because of the length of time involved in the past and a deficiency of the right kind of investigation recently; it also seems possible that the frequency and size of the passages was exaggerated in the past. Now, scores and hundreds of the same species have occurred again in the autumn of 1976 together with others which could well have been overlooked before the development of good binoculars, and further observation shows that examples of the same phenomena can be found regularly if an adequate watch is kept for them. The configuration of the coastline, involving a long 'leading line', with a scatter of good observation posts, makes occasionally for grandstand watching. The precise mechanism which makes more birds appear in some years, and also causes occasional wrecks (though these are usually more marked on the west coast), requires more study. Certain points, however, seem clear. Some of the species concerned, such as the large shearwaters, are highly pelagic and occur commonly only out in the Atlantic, while it seems 424 Seabird movements along the east coast oj England likely that the bulk of the population of others, such as the Pomarine and Long-tailed Skuas and especially Sabine's Gull, breeds in the American Arctic but migrates southeast across the Atlantic towards Iberia and west Africa (Bourne 1965). There is little evidence that many of these birds reach the North Sea through the English Channel—where surely by now they would have been seen from the south coast, as with the Pomarine Skuas on spring passage (Davenport 1975)?—or that they arrive overland. It seems likely that they must have wandered unusually far northeast in the late summer so that, when they turned south, they entered the North Sea around the north of Scotland. Presumably, the variation in the number of pelagic seabirds and trans• atlantic migrants that reach the North Sea must be caused by fluctuations in the strength of the prevailing westerly winds in the Atlantic during the period when the birds are moving. In the warm summer of 1976 in par• ticular, the subtropical high-pressure system extended unusually far north, leading to the development of a sustained westerly airflow farther north in the area where easterlies are quite regular on the north side of passing depressions. It seems likely that the seabirds first spread unusually far north with the fine weather, and then drifted east with the sustained westerly winds into the Norwegian Sea, so that, when they turned south, they entered the North Sea instead of passing down the west coast of Britain and Europe. C. J. G. Scharringa (in litt.) reported that there were also unusually many Manx and Sooty Shearwaters off the Netherlands in 1976, and these may have passed on through the Strait of Dover. Seitz & von Wicht (1980) also reported that nine times as many skuas as usual reached central Europe; 92% of them were young birds and Long-tailed Skuas (in early September) and Pomarine Skuas (later in the month) were unusually numerous. Their arrival was associated with the passage of low-pressure systems in the Atlantic and North Sea. It seems possible that some of the birds are able to recognise that they have gone astray, possibly from the change in the character of the water as it circulates around the North Sea (as discussed earlier), and beat back into the Atlantic around the north of Scotland, mingling with the local birds which regularly carry out such movements. A few transequatorial migrants also appear to remain in the North Sea for the winter—with the local Puffins Fratercula arctica,which, unlike those in Atlantic waters, do not leave for the south (Mead 1974)—sheltering from the prevailing west winds in the lee of the east coast of Britain, where they join the local birds and northern winter visitors which feed on the sprats Clupea sprattus which shoal offshore there at that season. This is, however, a risky proceeding, since they remain exposed to the east winds which cause such slaughter among the local birds in hard winters. Thus, the winter population of the more delicate species seems unlikely to increase. In view of the erratic way in which seabirds appear to move around freely for distances of hundreds of kilometres with every change of the weather, and variations in the extent to which this is noticed—with fluctuations in public interest in the subject—it seems doubtful whether it would be rewarding to try any further analysis of long-term variations, at least until Seabird movements along the east coast of England 425 better data become available. It also seems doubtful whether it is realistic to try to construct atlases of the distribution of birds at sea.

Acknowledgments The following observers responded to our appeal for records: Britain R. H. Appleby, K. Atkin, P.J. Brewster, G. P. Catley, J. Cudworth, Dr P.J. Dare, D. L. Davenport, R. H. Dennis, A. Dixon, A. S. Dowsett, F. Hamilton, P. Hope Jones, J. Hornbuckle, Dr A. G. Knox, P. Mash, N. V. McCanch, P. McCartney, J. McLoughlin, A. Paterson, S. R. D. da Prato, Dr A. P. Radford, P. S. Redman, N. Riddiford, M. J. Rogers, J. Rosetti, K. Walton; Europe Dr S. Allavena, M. P. Lee, C.J. G. Scharringa, P. Vandenbulke, DrJ. van Impe,J. Vielliard, Dru. von Wicht. We are grateful to them and also to P. A. Lassey, who maintains a register of all seabird counts made at Flamborough Head. The investigations in Scotland were carried out in the course of a study of the birds of the Forties oilfield financed by a grant from BP Petroleum Development Ltd to the Zoology Department, Aberdeen University, and made use of a cine camera supplied by Marconi Electronics Ltd and satellite photographs supplied by the Department of Electronics, Dundee University. Dr R. S. Bailey and H. D. Dooley provided advice about the marine environment, and D. L. Davenport provided assistance with the research and the form of this report.

Summary A combination of an inflow of water from the Atlantic around the north of Scotland and local mixing leads to the development of rich feeding-grounds for seabirds off the northeast coast of Britain. In addition to supporting large communities of breeding species and winter visitors, a variety of scarce species also accumulates in the area and takes part with the local birds in conspicuous coasting movements which commonly appear to involve compensation for drift by the wind out at sea. Birds in the Atlantic may also be drifted east past the north of Scotland by west winds in the Atlantic in some years, such as 1976, so that they enter the North Sea when they migrate south. Some may continue overland or through the Strait of Dover; others return around the north of Scotland to the Atlantic, and a few remain for the winter. Increased sea-watching in recent years now makes it necessary to revise the accepted pattern of distribution for a number of species, notably Cory's Calonectris diomedea, Manx Puffinuspuffinus and Little Shearwaters P. assimilis, Long-tailed Skua Stercorarius longicaudus and Sabine's Gull Larus sabini, which appear to reach the east coast of Britain more often than was realised before the development of improved binoculars and telescopes.

References BANNERMAN, D. A. 1963. The Birds of the British Isles, vol 12. Edinburgh & London. BOURNE, W. R. P. 1965. Birdwatching by submarine: a trip to Gibraltar in September. Seabird Bull. 1:34-37. 1967. Long-distance vagrancy in the petrels. Ibis 109: 141-167. 1976a. Seabirds in the Wash. Seabird Rep. 5: 18-21. 1976b. Birds of the North Atlantic Ocean. Proc. XVI Int. Orn. Congr. 705-715. 1978. The seabirds of the eastern North Atlantic. Ibis 120: 117-119. & HARRIS, M. P. 1979. Birds of the Hebrides: seabirds. Proc. Roy. Soc. Edinburgh 77B: 445-475. ——, KNOX, A. G., MERRIE, T. D. H., & MORLEY, A. H. 1979. The birds of the Forties Oilfield 1975-1978. North-east Scotland Bird Rep. (1978): 47-52. BRITISH ORNITHOLOGISTS' UNION. 1971. The Status of Birds in Britain and Ireland. Oxford, London & Edinburgh. CRAMP, S., BOURNE, W. R. P., & SAUNDERS, D. 1974. The Seabirds of Britain and Ireland. London. DAVENPORT, D. L. 1971. Autumn seabird movements in the Thames Estuary. Kent Bird Rep. (1969): 84-91. 1975. The spring passage of Pomarine Skuas on British and Irish coasts. Brit. Birds 68: 456-462. 1979. Spring skua passage at Balranald, North Uist. Scot. Birds 10: 216-221. ELKINS, N., & WILLIAMS, M. R. 1970. Seabird movements in north-east Scotland, 1968 and 1969. Seabird Rep. 1:31-39.