We studied the breeding performance of very old Common Terns (Sterna hirundo) at Bird Island, USA (41°40′N, 70°43′W), in 1999. We studied birds aged ≥18 yr, comprising the oldest 5% of the birds breeding at this site. We located 24 of these old birds and measured their breeding performance, including laying dates, clutch sizes, egg masses, hatching success, chick growth, chick survival, and overall productivity. We compared their performance with that of several reference groups, including a date-matched group of young birds aged 6–9 yr and date-matched birds of all ages. Breeding performance declined with laying date in all groups. The old birds were more successful in raising chicks than any of the reference groups. Within the group of old birds, breeding performance remained high or improved with age, even after controlling for effects of laying date. Males and females were represented equally among the group of old birds; there was no evidence that performance was higher among old males or old females. If the Common Terns at this site experience any senescent decline in breeding performance within their 20–25 yr lifespan, this must be offset either by increased reproductive effort or by selective survival of high quality individuals.
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Vol. 73 • No. 2