Do avian cooperative breeders live longer?

Cooperative breeding is not common in birds but intriguingly over-represented in several families, suggesting that predisposing factors, similar ecological constraints or a combination of the two facilitate the evolution of this breeding strategy. The life-history hypothesis proposes that cooperative breeding is facilitated by high annual survival, which increases the local population and leads to a shortage of breeding opportunities. Clutch size in cooperative breeders is also expected to be smaller. An earlier comparative analysis in a small sample of birds supported the hypothesis but this conclusion has been controversial. Here, I extend the analysis to a larger, worldwide sample and take into account potential confounding factors that may affect estimates of a slow pace of life and clutch size. In a sample of 81 species pairs consisting of closely related cooperative and non-cooperative breeders, I did not find an association between maximum longevity and cooperative breeding, controlling for diet, body mass and sampling effort. However, in a smaller sample of 37 pairs, adult annual survival was indeed higher in the cooperative breeders, controlling for body mass. There was no association between clutch size and cooperative breeding in a sample of 93 pairs. The results support the facilitating effect of high annual survival on the evolution of cooperative breeding in birds but the effect on clutch size remains elusive.

合作繁殖在鸟类中并不常见，但在多个类群中却异常富集，这提示潜在的促进因子、相似的生态限制条件，或是二者共同作用，推动了该繁殖策略的演化。生活史假说提出，合作繁殖的演化得益于较高的年存活率——这会提升本地种群规模，进而导致繁殖机会稀缺。合作繁殖类群的窝卵数预计也会更小。此前一项基于少量鸟类样本的比较分析曾支持该假说，但这一结论始终存在争议。
本研究将分析范围拓展至全球范围内的更大样本，并纳入了可能影响慢生活史与窝卵数估算的潜在混杂因素。在包含81对近缘合作繁殖与非合作繁殖物种的样本集中，在控制食性、体重与采样努力量的前提下，并未发现最大寿命与合作繁殖存在关联。不过在37对物种的较小样本中，在控制体重的前提下，合作繁殖类群的成体年存活率确实更高。在93对物种的样本中，窝卵数与合作繁殖之间未发现显著关联。本研究结果支持高年存活率对鸟类合作繁殖演化的促进作用，但窝卵数所受的影响仍不明确。