Bourne Amanda R, Ridley Amanda R, McKechnie Andrew E, Spottiswoode Claire N, Cunningham Susan J
FitzPatrick Institute of African Ornithology, DSI-NRF Centre of Excellence, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa.
Centre for Evolutionary Biology, School of Biological Sciences, University of Western Australia, Crawley 6009, Australia.
Conserv Physiol. 2021 Jun 16;9(1):coab043. doi: 10.1093/conphys/coab043. eCollection 2021.
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 , 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.
高气温对野生动物种群的繁殖有显著负面影响，包括对鸟类孵化过程的影响。了解驱动这些影响的机制需要全面掌握自然条件下动物的生理和行为。我们采用了一种新颖的组合方法，即无创双标记水（DLW）技术、巢温数据和实地行为观察，来测试温度、降雨和群体规模对南非干旱稀树草原地区特有的合作繁殖雀形目鸟类——南白脸鸫孵化期间生理和行为的影响。随着气温升高，亲鸟孵卵的时间比例下降，这种行为模式传统上被解释为利用环境温度进行孵化的好处。然而，我们发现：（i）当每日最高气温超过35.3°C时，卵的孵化几率小于50%；（ii）除炎热天气外，白脸鸫群体几乎持续（占白天时间的99%）孵卵；（iii）无人照看的巢内有效温度经常超过40.5°C，高于此温度鸟类胚胎有死亡风险；（iv）长时间孵卵的白脸鸫在炎热天气下无法维持水平衡；（v）参与孵卵群体中的白脸鸫在炎热天气下体重减轻。这些结果表明，白脸鸫可能在炎热时期离开巢穴，以降低在高有效温度下长时间孵卵导致脱水的风险。随着平均气温上升以及气候变化下极端高温事件变得更加频繁，鸟类在孵化过程中可能会承受越来越大的体温调节成本，导致巢内照看时间减少，卵过热的可能性增加，这对巢穴成功率乃至最终的种群存续都有影响。
