Status, productivity, movements and morality of great Cormorants Phalacrocorax Carbo breeding in Caithness, Scotland: a study of a declining population
Atlantic seabirds , Volume 2 - Issue 3/4 p. 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 he 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.
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D. Budworth, M. Canham, H. Clark, B. Hughes, & R.M. Sellers. (2000). Status, productivity, movements and morality of great Cormorants Phalacrocorax Carbo breeding in Caithness, Scotland: a study of a declining population. Atlantic seabirds, 2(3/4), 165–180.
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