Data from: Early mortality saves energy: estimating the energetic cost of excess offspring in a seabird

Offspring are often produced in excess as insurance against stochastic events or unpredictable resources. This strategy may result in high early-life mortality, yet age-specific mortality before offspring independence and its associated costs have rarely been quantified. In this study, we modelled age-specific survival from hatching to fledging using 24 years of data on hatching order (HO), growth and age of mortality of more than 15 000 common tern (Sterna hirundo) chicks. We found that mortality peaked directly after hatching, after which it declined rapidly. Mortality hazard was best described with the Gompertz function, and was higher with later HO, mainly due to differences in baseline mortality hazard, rather than age-dependent mortality. Based on allometric mass–metabolism relationships and detailed growth curves of starving chicks, we estimated that the average metabolizable energy intake of non-fledged chicks was only 8.7% of the metabolizable energy intake of successful chicks during the nestling phase. Although 54% of hatchlings did not fledge, our estimates suggest them to have consumed only 9.3% of the total energy consumption of all hatched chicks in the population before fledging. We suggest that rapid mortality of excess offspring is part of an adaptive brood reduction strategy to the benefit of the parents.

生物通常会过量繁殖后代，以此作为应对随机事件或不可预测资源的保障策略。该策略可能会导致较高的早期死亡率，但子代独立前的年龄特异性死亡率及其相关成本却鲜有量化研究。本研究基于24年间收集的15000余只普通燕鸥（Sterna hirundo）雏鸟的出雏顺序（hatching order, HO）、生长情况及死亡日龄数据，对雏鸟从破壳到离巢的年龄特异性存活率进行了建模分析。研究发现，死亡率在破壳后即刻达到峰值，随后迅速下降。死亡风险率最适合用冈珀茨函数（Gompertz function）进行拟合，且出雏顺序越靠后的个体死亡风险率越高，这主要源于基线死亡风险率的差异，而非年龄依赖性死亡率的不同。基于异速生长质量-代谢关系以及饥饿雏鸟的详细生长曲线，本研究估算得出：育雏期内，未成功离巢雏鸟的平均可代谢能量摄入仅为成功离巢雏鸟的8.7%。尽管有54%的破壳雏鸟未能成功离巢，但估算结果显示，这些雏鸟在离巢前消耗的总能量仅占种群内所有破壳雏鸟总能量消耗的9.3%。我们提出，过量子代的快速死亡属于适应性育雏缩减策略的一部分，该策略可使亲代获益。