Movements and mortality rates of Great Skuas ringed in Scotland

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Abstract
Al rings fall off great skuas [Stercorarius skua] after 2-5 yr, but monel rings, used since 1963 on Foula, suffer negligible wear. Proportions of recoveries reported as killed, caught, exhausted or found dead vary geographically and differ between 1st-yr and older birds. Since 1966 the recovery rate of 1st-year birds has fallen significantly and recoveries in the North Sea now form a smaller proportion of the total, due either to a reduction in frequency of westerly winds or to the evolution of a more pelagic autumn dispersal into the Atlantic. Bad weather in autumn affects all age groups, and recovery rates of cohorts in successive seasons are also correlated, indicating that birds may take more than 1 yr to recover from effects of bad weather. First-year birds move to southwestern Europe in winter, with most off the coast of Iberia. In summers before the 5th yr some visit high latitudes between Greenland and Spitsbergen [Norway]. Winter movements become shorter, with many birds remaining in British waters when more than 5 yr old. Adult survival is estimated to be 93% per annum and 1st-yr survival 80%.