ATLANTIC SEABIRDS

Contents and abstracts issue 2(3/4) published April 2001

Tasker M.L. 2000. The UK and Ireland seabird monitoring programme - a history and introduction. Atlantic Seabirds 2(3/4): 97-102.

[no abstract provided]

Thompson K.R. & Walsh P.M. 2000. Population trends and breeding success of cliff-nesting seabirds in Orkney, 1976-98. Atlantic Seabirds 2(3/4): 103-132.

Population trends of Northern Fulmars, Kittiwakes, Common Guillemots and Razorbills have been monitored in sample plots at five colonies in Orkney since 1976; several complete counts of these colonies were also made. Numbers of Fulmars, Guillemots and Razorbills attending the colonies in the breeding season increased from 1976 to 1997. However, for all three species, the overall increase was punctuated by a period of decline in the early 1980s; there was also some variation between colonies in population trends. In contrast to the other species, breeding numbers of Kittiwakes declined by an average of 2.5% per annum over the same period, the overall rate of decline being inversely related to colony size. Breeding success of Fulmars, Kittiwakes and Guillemots was monitored annually for varying periods from the mid 1980s to late 1990s. Breeding success of both Fulmars and Guillemots was close to or above national averages in most years. Kittiwake breeding success was generally very high in the past 10-15 years, so the declining population appears paradoxical. Large-scale mortality of fledglings in some years, particularly the late 1970s, may be partially responsible but the continuing decline of the Orkney Kittiwake population remains to be fully explained.

Harris M.P., S. Wanless & P. Rothery 2000. Adult survival rates of Shag Phalacrocorax aristotelis, Common Guillemot Uria aalge, Razorbill Alca torda, Puffin Fratercula arctica and Kittiwake Rissa tridactyla on the Isle of May 1986-96. Atlantic Seabirds 2(3/4): 133-150.

On the Isle of May between 1986 and 1996, the average adult survival of Shags Phalacrocorax aristotelis was 82.1%, Common Guillemots Uria aalge 95.2%, Razorbills Alca torda 90.5%, Puffins Fratercula arctica 91.6% and Kittiwakes Rissa tridactyla 88.2%. Shags, Razorbills and Puffins all had a single year of exceptionally low survival but these years did not coincide. In contrast, Kittiwake survival declined significantly over the period and there was evidence that substantial non-breeding occurred in several years. Breeding success of Kittiwakes also declined, which gives rise to concern for its future status. Given a high enough level of resighting, return rates (the proportion of birds known to be alive one year that were seen the next year) on a year-by-year basis provide a reasonable indication of relative changes in adult survival.

Swann R.L. 2000. Integrated seabird monitoring studies on the Isle of Canna, Scotland 1969-99. Atlantic Seabirds 2(3/4): 151-164.

An annual survey of breeding seabird numbers on the Isle of Canna, western Scotland, was established in 1969; the breeding productivity of several species is also monitored each year. Over 53 000 seabirds have been ringed since the study started and the subsequent recoveries and recaptures have been used to assess changes in survival rates and return rates to the island. Northern Fulmars Fulmarus glacialis have shown great fluctuations in numbers since 1973 and from 1996-99 there has been a noticeable decline accompanied by a decrease in breeding output. The percentage of study burrows occupied by Manx Shearwaters Puffinus puffinus began to decline in the late 1980s and breeding success has also declined; the species is now close to extinction on the island. Shags Phalacrocorax aristotelis, Kittiwakes Rissa tridactyla and Common Guillemots Uria aalge all showed a steady increase in numbers up to the mid 1980s, after which numbers declined or, in the case of Guillemots, stabilised until the early 1990s when further increases took place. During the periods of population growth return rates of young Shags and Guillemots were high but they subsequently declined during the period of population decline/stability and in the case of Guillemot this was linked to a significant increase in first-year recovery rates. The period of decline was also associated with a drop in Shag and Kittiwake breeding output. These changes were probably driven by fluctuations in the food supply, although increased predation might have affected Fulmar and Manx Shearwater numbers.

Budworth D., M. Canham, H. Clark, B. Hughes & R.M. Sellers 2000. Status, productivity, movements and mortality of Great Cormorants Phalacrocorax Carbo breeding in Caithness, Scotland: A study of a declining population. Atlantic Seabirds 2(3/4): 165-180.

This paper describes the results of a study of the Great Cormorant Phalacrocorax carbo breeding in Caithness, Scotland, with particular emphasis on its recent status and distribution based on annual surveys carried out between 1992 and 1998, its breeding productivity, diet, mortality and movements. Breeding numbers declined from 842 apparently occupied nests in 1969, to c. 230 in 1985-93, and 90-180 in 1994-98, an overall reduction of 80-90% in 30 years. Over the same period, the number of colonies declined from 12 to five. Breeding productivity varied between 2.18 and 3.20 chicks per successful nest, which is within the normal range of variation found elsewhere in Britain. Nestling diet consisted mainly of sandeels Ammodytes spp., according with earlier studies in Caithness. Ringing recoveries show the main winter quarters to be the coasts of the Moray Firth and the rivers that flow into it; fewer numbers move further south along the east coast of Scotland, mainly to the Firths of Tay and Forth but some birds reach southern England. A secondary route extends down the Great Glen (or possibly across the Central Lowlands) to wintering areas along the west coast of Scotland and north-west England, with a few birds crossing to Northern Ireland. Ringing recoveries also show that adult Cormorants from Caithness suffer rather higher mortality rates than birds elsewhere in Britain. The reasons for the declines in breeding numbers are discussed, the most likely cause being reduced adult survival, possibly caused by excessive shooting, although emigration of some birds to other areas to breed is a potential contributory factor.

Craik J.C.A. & Campbell B. 2000. Bruce Campbell's islands revisited: Changes in the seabirds of Loch Sunart after half a century. Atlantic Seabirds 2(3/4): 181-194.

In 1950 and 1998, counts were made of nine bird species breeding on 31 small islands in Lochs Sunart and Teacuis, sealochs that are typical of many in western Scotland. During this 48-year period, some species that were once characteristic breeding birds of islands in sealochs decreased greatly or disappeared; these included Common Eider, Common Gull, Common Tern and Black Guillemot. Numbers of Heron and Oystercatcher changed very little. Herring Gull and Great Black-backed Gull numbers both increased greatly; in recent years these increases took place at a single island at the mouth of Loch Sunart where they bred successfully. The increase in Herring Gull numbers was contrary to a wider regional trend in the period 1989-98. Records from the two lochs of seabird numbers, breeding success and causes of failure during 1990-98 suggest that two quite separate influences were at work. Excess feed from six large salmon farms may have played an important part in the local increase of large gulls, and the arrival and spread of American Mink caused the breeding failures of terns and Common Gulls that accompanied their declines. The decreases reflect changes during 1987-98 over a larger area of west Scotland, where five gull and tern species each declined by c. 40-50% following widespread annual breeding failures that are known to have been caused by mink.

Perrins C.M. & S.B. Smith 2000. The breeding Larus gulls on Skomer Island National Nature Reserve, Pembrokeshire. Atlantic Seabirds 2(3/4): 195-210.

The populations of breeding Lesser Black-backed Gull Larus fuscus, Herring Gull Larus argentatus and Great Black-backed Gull Larus marinus on Skomer Island have all changed dramatically since the island became a National Nature Reserve in 1959. The role of human activities in these changes is marked and includes bird protection and other conservation measures, reduction in numbers by culling, and changes in food availability. Gulls and other seabirds have been well-studied on Skomer and population trends are considered in relation to adult survival rates, annual productivity and other factors.

Ratcliffe N., G. Pickerell & E. Brindley 2000 Population trends of Little and Sandwich Terns Sterna albifrons and S. sandvicensis in Britain and Ireland from 1969 to 1998. Atlantic Seabirds 2(3/4): 211-226.

Population trends of Little Terns Sterna albifrons and Sandwich Terns S. sandvicensis were determined between 1969 and 1998 using counts from sample colonies throughout the UK and Ireland. The Sandwich Tern population increased from c. 12 000 pairs in 1969 to c. 17 000 pairs in 1971, but then fell to c. 13 000 pairs in 1974. It then recovered at a rate of 6% per annum to c. 17 000 pairs in 1979 and fluctuated around 16 000 pairs until 1992. There was a second large population decline of 20% between 1992 and 1995, resulting in a total of c. 13 000 pairs in 1995. This decline appears to have halted up to 1998, when population size remained relatively stable at 13 500-14 000 pairs. The Little Tern population increased from 2000 pairs in 1969 to 2600 pairs in 1971 and then decreased to c. 1800 pairs in 1973. It increased again to a peak of 2800 in 1975 but then entered a long-term decline at an average rate of 1.23% per annum, punctuated by increases in 1988 and 1996. The population of c. 1700 in 1998 was the lowest recorded during the 30 year study and represents a 39% decline compared with 1975. The decline in Sandwich Tern populations appears to be confined primarily to the North Sea, with decreases being associated with events at individual colonies rather than at all colonies within the area. The declines in Little Tern populations appear to have occurred throughout the species range and are probably symptomatic of a chronic, widespread problem. Possible reasons for the declines in these populations are discussed and recommendations are made for further research, monitoring and conservation measures.

Heubeck M. 2000. Population trends of Kittiwake Rissa tridactyla, Black Guillemot Cepphus grylle and Common Guillemot Uria aalge in Shetland, 1978-98. Atlantic Seabirds 2(3/4) Special Issue: 227-244.

Kittiwake Rissa tridactyla numbers in Shetland, monitored by periodic nest counts at all colonies, declined from 54 600 pairs in 1981 to 23 000 pairs in 1998, probably due to low food availability and increased predation by Great Skuas Catharacta skua. Pre-breeding counts of Black Guillemots Cepphus grylle along selected stretches of coastline showed variable trends. In Yell Sound, an increase of 155% between 1983 and 1998 probably represented recovery after mortality from oil pollution in 1979. Elsewhere, some decreases were associated with localised oil pollution. Common Guillemot Uria aalge numbers at four colonies increased in the late 1970s and early 1980s, but then declined up to 1990; thereafter, numbers increased at all colonies. At the largest colony, Guillemot numbers had returned to their previous peak by the mid 1990s, but at the three smaller colonies they remained at c. 50% of early 1980s levels. Large-scale change in food availability in the North Sea is thought to have caused increased winter mortality during the early 1980s, whereas reduced abundance of sandeels may have contributed to reduced colony attendance of non-breeding and off-duty birds and therefore apparently low population levels from 1989-91.