Data from: Multiple benefits of alloparental care in a fluctuating environment

Although cooperatively breeding vertebrates occur disproportionately in unpredictable environments, the underlying mechanism shaping this biogeographic pattern remains unclear. Cooperative breeding may buffer against harsh conditions (hard life hypothesis), or additionally allow for sustained breeding under benign conditions (temporal variability hypothesis). To distinguish between the hard life and temporal variability hypotheses, we investigated whether the number of alloparents at a nest increased reproductive success or load-lightening in superb starlings (Lamprotornis superbus), and whether these two types of benefits varied in harsh and benign years. We found that mothers experienced both types of benefits consistent with the temporal variability hypothesis, as larger contingents of alloparents increased the number of young fledged while simultaneously allowing mothers to reduce their provisioning rates under both harsh and benign rainfall conditions. In contrast, fathers experienced load-lightening only under benign rainfall conditions, suggesting that cooperative breeding may serve to take advantage of unpredictable benign breeding seasons when they do occur. Cooperative breeding in unpredictable environments may thus promote flexibility in offspring care behaviour, which could mitigate variability in the cost of raising young. Our results highlight the importance of considering how offspring care decisions vary among breeding roles and across fluctuating environmental conditions.尽管合作繁殖（cooperative breeding）的脊椎动物在不可预测环境中出现的比例偏高，但塑造这一生物地理格局的内在机制仍不明晰。合作繁殖既可能缓冲恶劣环境压力（艰难生活假说，hard life hypothesis），也可使种群在温和环境中维持持续繁殖（时间变异性假说，temporal variability hypothesis）。为区分艰难生活假说与时间变异性假说，我们以丽椋鸟（Lamprotornis superbus）为研究对象，探究巢内异亲抚育者（alloparents）的数量是否提升了繁殖成功率，或是实现了抚育负荷减轻（load-lightening），并分析这两类收益在恶劣与温和降雨年份中是否存在差异。研究结果显示，雌性亲鸟同时获得了两类收益，契合时间变异性假说：在恶劣与温和降雨条件下，更多的异亲抚育者不仅提升了出巢幼鸟数量，同时还能降低雌性亲鸟自身的育雏投喂率。与之相反，雄性亲鸟仅在温和降雨条件下才会获得抚育负荷减轻的收益，这表明合作繁殖或可帮助种群抓住偶发出现的温和繁殖季。因此，不可预测环境中的合作繁殖或可提升后代抚育行为的灵活性，从而缓解育雏成本的波动。本研究结果强调，需关注不同繁殖角色的后代抚育决策，以及其随环境波动产生的变化。