Year-round movements of female Common Scoter Melanitta nigra nesting in Scotland; birds of a feather don’t flock together

Abstract

Numbers of breeding Common Scoter Melanitta nigra have declined in Britain and Ireland since the mid-1990s. To investigate little-known aspects of their annual cycle, nine nesting females at four of the main breeding sites in Scotland (in Inverness-shire, Perth and on Islay) were fitted with unique coloured leg rings and global location sensing (GLS) daylight loggers to track their year-round migrations and wintering areas. Unsuccessful breeders (failing at eggs or duckling stage) left the nesting areas and arrived on the sea from 22 July to 7 August (n = 10) with successful breeders (young reared to > 10 days) arriving between 18 and 20 August (n = 2). In December to February, when movements were at a minimum, the birds were widely dispersed at locations including the Moray Firth, (northeastern Scotland), the west and east coast of Ireland, Liverpool Bay (mid-western England) and the west coast of Morocco. The results from GLS deployed on female Common Scoter are the first to link breeding, staging and wintering areas in this species in time and space, showing Scottish-breeding birds wintered at sites from the north to the southerly extent of their known winter distribution. One of the birds wintering off Morocco staged off the Netherlands before returning to Scotland. All birds arrived back on the breeding sites between 13 and 30 April (n = 10). The apparent high survival rate and strong philopatry of female Common Scoters suggest that low reproductive output and/or low first-year survival contribute to the observed decline in breeding numbers, supporting the need for current conservation actions at the Inverness-shire breeding sites to protect the species.