Ageing gracefully: physiology but not behaviour declines with age in a diving seabird, Funct. Ecol. (in press

1. A higher proportion of long-lived animals die from senescence than short-lived animals, yet many long-lived homeotherms show few signs of physiological ageing in the wild. This may, however, differ in long-lived diving homeotherms that frequently encounter hypoxic conditions and have very high metabolic rates. 2. To examine ageing within a long-lived diving homeotherm, we studied resting metabolism and thyroid hormones (N = 43), blood oxygen stores (N = 93) and foraging behaviour (N = 230) of thick-billed murres (Uria lomvia). Because murres dive exceptionally deep for their size and have a very high metabolism, we expected that ageing murres would show signs of physiological senescence. We paid particular attention to resting metabolism as we argue that these maintenance costs reflect those experienced during deep dives. 3. Blood oxygen stores (haematocrit), resting metabolic rate and thyroid hormone levels all declined significantly with age in incubating murres 3–30 years of age. In birds measured longi-tudinally 3 years apart, thyroid hormone levels and haematocrit were both significantly lower, suggesting progressive changes within individuals rather than selective disappearance of indi-viduals with high metabolic rates. Within our longitudinal data set, we found no effect of ag