Parental overproduction is hypothesized to hedge against uncertainty over food availability and stochastic death of offspring, and to improve brood fitness. Understanding the evolution of overproduction requires quantifying its benefits to parents across a wide range of ecological conditions, which has rarely been done. Using a multiple hypotheses approach and 30 years of data, we evaluated the benefits of overproduction in the Blue-footed booby, a seabird that lays up to three eggs asynchronously, resulting in an aggressive brood hierarchy that facilitates the death of last-hatched chicks under low food abundance. Results support the resource-tracking hypothesis, as low prey abundance (estimated from sea surface temperature and chlorophyll-a concentration) led to rapid brood reduction. The insurance hypothesis was supported in broods of three, where last-hatched chicks’ survival increased after a sibling’s death. Conversely, in broods of two, results suggested that parents abandoned last-hatched chicks following first-hatched chicks’ deaths. No direct evidence supported the facilitation hypothesis: presence of a last-hatched chick during development did not enhance its sibling’s fitness in the short or long term. The value of last-hatched offspring to parents, as “extra” or “insurance” varied with indices of food abundance, brood size, and parental age. Ninety percent of overproduction benefit came from enabling parents to capitalize on favorable conditions by fledging additional offspring. Our study provides insight into the forces driving overproduction, explaining the adaptiveness of this apparently wasteful behavior and allowing us to better predict how overproduction’s benefits might be modified by ocean warming.

中文翻译：

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父母的过度生产使得自相残杀的鸟类能够根据气候驱动的猎物变化来调整巢穴大小

假设父母的过度生产是为了对冲食物供应的不确定性和后代的随机死亡，并提高育雏适应性。要了解生产过剩的演变，需要量化其在各种生态条件下给父母带来的好处，但目前很少有人这样做。使用多重假设方法和 30 年的数据，我们评估了蓝脚鲣鸟过度生产的好处，蓝脚鲣鸟是一种异步产下最多三个蛋的海鸟，导致了具有侵略性的巢穴等级结构，导致最后孵出的雏鸟死亡。食物丰富度低。结果支持资源追踪假说，因为猎物丰度低（根据海面温度和叶绿素 a 浓度估计）导致幼崽迅速减少。保险假说在三只雏鸡中得到了支持，其中最后孵出的雏鸡在兄弟姐妹死亡后存活率增加。相反，在两只雏鸡中，结果表明，父母在第一批雏鸡死亡后抛弃了最后孵出的雏鸡。没有直接证据支持促进假说：发育过程中最后孵出的小鸡的存在并不会在短期或长期内增强其兄弟姐妹的健康状况。最后孵出的后代对父母的价值（作为“额外”或“保险”）随着食物丰富程度、孵化规模和父母年龄的指数而变化。百分之九十的生产过剩收益来自于使父母能够利用有利的条件，生育更多的后代。我们的研究深入了解了导致生产过剩的力量，解释了这种明显浪费行为的适应性，并使我们能够更好地预测海洋变暖如何改变生产过剩的好处。