Changes in recovery and retrap patterns of Guillemots ringed on Canna 1974–85

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Abstract
Swann, R. L., Aiton, D. G., Carruthers, J., Graham, R. & Ramsay A. D. K. 1989. Changes in recovery and retrap patterns of Guillemots ringed on Canna 1974–85. Ring. & Migr. 10: 35–40. Breeding Guillemot numbers have been monitored on Canna since 1974. Numbers increased continuously up until 1983, since when they have declined slightly. Results from large scale ringing show that, over the study period, the mortality rates of adult and immature birds, as shown by recoveries, have not altered significantly. Since 1980, however, the recovery rate of first year birds has increased significantly with relatively more being found dead in mid-winter. Since 1983 significantly fewer 4–7 year old birds have returned to breeding colonies on the island. It is suggested that lower recruitment levels, due to increased mortality of first year birds, has resulted in the colony ceasing to grow in numbers since 1983.