Data from: Don't put all eggs in one nest - spread them and cut time at risk

In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are debated. Using mathematical modelling and field observations we analyse an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, a parasitic female by spreading her eggs can reduce offspring time in the vulnerable nest, at risk of predation or other destruction. The model suggests that she can achieve much of this benefit already by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a much larger than average clutch, without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproductive success. These results help explain the puzzle of nesting parasites in some precocial birds, which lay eggs in the nests of other females before laying in their own nest. Risk reduction by egg spreading may also play a role in the evolution of other breeding systems, for instance some forms of polyandry with male parental care.

在诸多产卵动物类群中，部分雌性个体将其所产的窝卵（clutch）分散至多个巢穴内。这种繁殖策略的适合度（fitness）效应长期存在学术争议。我们通过数学建模与野外观测，分析了巢寄生（brood parasitic）类群及其他繁殖系统中，分散产卵的一项未被探讨过的优势：缩短后代所处的风险时长。若一窝卵需要多日才能完成产卵并启动孵化，且胚胎发育始于最后一枚卵产出之后，雌性巢寄生个体通过分散产卵，即可缩短后代在易被捕食或遭受其他破坏的脆弱巢穴中的停留时长。模型结果显示，即便雌性个体的总窝卵数较多，仅需将卵分散至少量巢穴中，即可获得该优势的绝大部分收益。针对鹊鸭（Bucephala clangula）的野外观测数据表明，分散产卵能够让繁殖力较强的雌性个体产出远超种群平均水平的窝卵数，且不会增加后代在单巢穴内的风险时长。该优势会随雌性个体的身体状态（繁殖力）提升而增强，并可显著提高雌性的繁殖成功率。这些结果有助于解释部分早成鸟（precocial birds）的巢寄生现象之谜：这类鸟类会先将卵产于其他雌性的巢穴中，之后再在自身巢穴内产卵。分散产卵带来的风险降低效应，或许也在其他繁殖系统的演化中发挥了作用，例如部分由雄性参与育幼的一妻多夫制（polyandry）繁殖策略。