The status and distribution of the Red-throated Diver Gavia stellata in Britain in 1994

The first national survey of breeding Red-throated Divers Gavia stellata in Britain was carried out in 1994. It was based on two visits to all standing freshwater in Shetland and Orkney, and to a sample elsewhere in the species' range in Scotland (Inner and Outer Hebrides and mainland). The survey located an estimated 855 breeding pairs (95% CI 735–990) and 1295 (95% CI 1075–1525) non-breeding adults. About 12% of birds that were recorded as non-breeding probably bred, but were not proved to do so; taking these into account the corrected total population for Scotland was estimated at 935 breeding pairs, with approximately 430 (46%) of these in Shetland, 105 (11%) in Orkney and 400 (43%) elsewhere in Scotland. In total, there were an estimated 3010 (95% CI 2685–3360) adult Red-throated Divers in Scotland during summer 1994. The Red-throated Diver population in Shetland has declined by more than a third since 1983, that in Orkney is probably stable and trends elsewhere are unknown. A comparison with Red-throated Diver populations on the Northern Isles showed that on the mainland densities were very much lower, that a smaller proportion of the birds present bred, that they did so on much larger lochs and that when they did breed they were less successful. In Shetland, breeding pairs on small lochs were more successful than those on large lochs; some potential reasons for this are discussed.