Data from: Ageing gracefully: physiology but not behaviour changes with age in a diving seabird

A higher proportion of long-lived animals die from senescence than short-lived animals, yet many long-lived homeotherms show few signs of physiological aging in the wild. This may, however, differ in long-lived diving homeotherms that frequently encounter hypoxic conditions and have very high metabolic rates. To examine aging 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 aging 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. Blood oxygen stores (hematocrit), resting metabolic rate and thyroid hormone levels all declined significantly with age in incubating murres 3-30 years of age. In birds measured longitudinally three years apart, thyroid hormone levels and hematocrit were both significantly lower, suggesting progressive changes within individuals rather than selective disappearance of individuals with high metabolic rates. Within our longitudinal dataset, we found no effect of age on dive depth, dive shape, or behavioural aerobic dive limit. A meta-analysis of changes in resting metabolism with age across 15 animal species demonstrated that such declines are pervasive across most of the kingdom. The rate of decline was highest in species with high energy expenditure supporting a linkage between metabolism and senescence. Physiological changes occurred in tandem with advancing age in murres, but offset each other such that there was no detectable decline in behavioural performance.

相较于短寿命动物（short-lived animals），长寿命动物（long-lived animals）因衰老（senescence）致死的比例更高，但多数长寿命恒温动物（homeotherms）在野外几乎无生理衰老迹象。不过，频繁暴露于低氧（hypoxic）环境且代谢率极高的长寿命潜水恒温动物，其衰老特征或存在差异。
为探究长寿命潜水恒温动物的衰老状况，我们以厚嘴海鸦（*Uria lomvia*，thick-billed murres）为研究对象，针对43只个体检测其静息代谢（resting metabolism）与甲状腺激素（thyroid hormones）水平、93只个体测定其血氧储备（血细胞比容（hematocrit））、230只个体分析其觅食行为（foraging behaviour）。鉴于厚嘴海鸦按体型而言潜水深度极深且代谢率极高，我们推测衰老的海鸦会表现出生理衰老迹象。我们尤为关注静息代谢指标，因为这类维持成本可反映深潜过程中个体所承受的代谢负荷。
在年龄为3至30岁的孵卵海鸦中，其血氧储备、静息代谢率（resting metabolic rate）与甲状腺激素水平均随年龄增长显著下降。对间隔三年开展重复测量的个体而言，其甲状腺激素水平与血细胞比容均显著降低，这表明个体内部存在进行性变化，而非高代谢率个体的选择性消失。在我们的纵向数据集内，未发现年龄对潜水深度、潜水形态或行为学有氧潜水极限（aerobic dive limit）存在影响。
针对15个动物物种的静息代谢随年龄变化开展的元分析（meta-analysis）表明，这类代谢水平下降现象在动物界的多数类群中普遍存在。能量消耗（energy expenditure）较高的物种，其代谢水平下降速率最快，这支持了代谢与衰老之间存在关联的观点。
厚嘴海鸦的生理变化随年龄增长同步出现，但这些变化相互抵消，因此未观测到行为表现出现显著下降。