A census of Arctic Terns was carried out in Orkney and Shetland in 1994. The results indicated that the population in the Northern Isles as a whole was 32 400 (95% CI = 26 600-39 000), a decline of 27% (95% CI = 12-40%) since 1989. A population model indicated that this decline could be explained by poor natal recruitment following breeding failures on Shetland between 1985 and 1990 (Table 1). Within the two archipelagos, numbers declined by 47.5% in Orkney to approximately 15 600 birds, while in Shetland the population remained stable at 16 800 birds (95% CI = 11 400- 23 800 birds). This is contrary to the predictions of the population model, which suggested a large decline in Shetland and a slight decline on Orkney. The best explanation for this discrepancy is that between 9000 and 10 000 Arctic Terns migrated from Orkney to Shetland, probably to exploit the increase in sandeel abundance there. The tern populations on Shetland and Orkney can therefore be regarded as components of a larger metapopulation.

Atlantic seabirds

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Nederlandse Zeevogelgroep

Emma Brindley, G. Mudge, N. Dymond, C. Lodge, B. Ribbands, D. Steele, … N. Ratcliffe. (1999). The status of Arctic terns Sterna paradisaea at Shetland and Orkney in 1994. Atlantic seabirds, 1(3), 135–143.