High air temperatures have measurable negative impacts on reproduction in wild animal populations, including during incubation in birds. Understanding the mechanisms driving these impacts requires comprehensive knowledge of animal physiology and behaviour under natural conditions. We used a novel combination of a non-invasive doubly labelled water (DLW) technique, nest temperature data and field-based behaviour observations to test effects of temperature, rainfall and group size on physiology and behaviour during incubation in southern pied babblers Turdoides bicolor, a cooperatively breeding passerine endemic to the arid savanna regions of southern Africa. The proportion of time that clutches were incubated declined as air temperatures increased, a behavioural pattern traditionally interpreted as a benefit of ambient incubation. However, we show that (i) clutches had a <50% chance of hatching when exposed to daily maximum air temperatures of >35.3°C; (ii) pied babbler groups incubated their nests almost constantly (99% of daylight hours) except on hot days; (iii) operative temperatures in unattended nests frequently exceeded 40.5°C, above which bird embryos are at risk of death; (iv) pied babblers incubating for long periods of time failed to maintain water balance on hot days; and (v) pied babblers from incubating groups lost mass on hot days. These results suggest that pied babblers might leave their nests during hot periods to lower the risk of dehydration associated with prolonged incubation at high operative temperatures. As mean air temperatures increase and extreme heat events become more frequent under climate change, birds will likely incur ever greater thermoregulatory costs of incubation, leading to compromised nest attendance and increased potential for eggs to overheat, with implications for nest success and, ultimately, population persistence.

中文翻译：

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脱水风险与合作繁殖的鸟类——南方斑鸬鹚 Turdoides bicolor 的巢穴出勤率和孵化成功率有关

高温对野生动物种群的繁殖产生了可衡量的负面影响，包括在鸟类孵化期间。了解驱动这些影响的机制需要全面了解自然条件下的动物生理和行为。我们使用了非侵入性双标记水 (DLW) 技术、巢穴温度数据和基于现场的行为观察的新组合，以测试温度、降雨量和群体规模对南方斑鸫双色乌龟孵化期间生理和行为的影响，南部非洲干旱稀树草原地区特有的合作繁殖雀形目。随着气温升高，离合器孵化的时间比例下降，这种行为模式传统上被解释为环境孵化的好处。然而，我们表明 (i) 离合器在暴露于 > 35.3°C 的每日最高气温时孵化的机会小于 50%；(ii) 除了炎热的日子，花斑鹛群几乎不断地孵化它们的巢穴（99% 的白天时间）；(iii) 无人看管的巢穴中的工作温度经常超过 40.5°C，高于此温度，鸟类胚胎就有死亡风险；(iv) 斑鸫长时间孵化，在炎热天气未能保持水分平衡；(v) 孵化组中的花斑咝咝声在炎热的日子里失去了质量。这些结果表明，在高温时期，花斑咿呀学语可能会离开它们的巢穴，以降低与在高操作温度下长时间孵化相关的脱水风险。随着平均气温升高和极端高温事件在气候变化下变得更加频繁，