Data from: Complete brood failure in an altricial bird is almost always associated with the sudden and permanent disappearance of a parent

1) A central goal in evolutionary ecology is to identify factors that explain variation in reproductive success, i.e. in the number of offspring produced. In altricial birds, a substantial part of this variation is determined by the number of nestlings that die before fledging, but the proximate cause of offspring mortality at a given nest is often unknown. 2) We used a uniquely comprehensive dataset of parental nestbox visits from seven breeding seasons to investigate the association between parental behaviour and nestling mortality in a population of blue tits (Cyanistes caeruleus). 3) In almost all nests that suffered complete brood mortality one of the parents had suddenly disappeared during the nestling stage. In contrast, parental disappearance in nests with partial brood mortality was rare and equally common as in nests with no brood loss. 4) With few exceptions, parents that disappeared during the nestling stage were never observed again and never returned to breed. In contrast, parents that remained after their partner disappeared were equally likely to be observed again or return to breed as parents of nests where both parents stayed. Visit rates at nests where a parent would disappear did not differ from those at nests where both parents stayed. 5) Taken together, our results show that - in contrast to partial brood failure - complete brood failure is almost always associated with the sudden and permanent disappearance of one of the parents, probably due to predation. Partial and complete brood mortality should therefore be treated as distinct processes that have different underlying causes.

1) 进化生态学（evolutionary ecology）的核心研究目标之一，是探明可解释繁殖成功率——即所产后代个体数量——变异的影响因子。对于晚成鸟（altricial birds）而言，该类变异的绝大部分由雏鸟离巢前死亡的数量决定，但特定巢窝内雏鸟死亡的近因（proximate cause）往往难以明确。2) 本研究依托覆盖7个繁殖季的全面详尽的亲鸟巢箱到访数据集，对蓝山雀（Cyanistes caeruleus）种群中亲鸟行为与雏鸟死亡率之间的关联进行了调查。3) 在几乎所有发生全巢雏鸟死亡的巢窝中，均有一只亲鸟在雏鸟抚育阶段突然失踪；与之形成鲜明对比的是，发生部分雏鸟死亡的巢窝中，亲鸟失踪的情况极为罕见，其发生频率与无雏鸟死亡的巢窝相当。4) 除极少数特例外，雏鸟抚育阶段失踪的亲鸟此后再未被观测到，也未返回该区域参与繁殖。与之相反，在配偶失踪后仍留守的亲鸟，其再次被观测到或返回繁殖的概率，与双亲均留守的巢窝中的亲鸟并无显著差异。即将发生亲鸟失踪的巢窝，其亲鸟的到访频率与双亲均留守的巢窝并无不同。5) 综合上述研究结果，本研究表明：与部分雏鸟死亡的情况不同，全巢失败几乎始终与某一只亲鸟的突发性永久性失踪相关，该现象大概率由捕食（predation）作用所致。因此，部分雏鸟死亡与全巢死亡应被视作两类独立的过程，其背后的驱动机制存在本质差异。