South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, Pretoria 0001, South Africa
DSI-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
J Exp Biol. 2021 Feb 24;224(Pt 4):jeb232777. doi: 10.1242/jeb.232777.
At a global scale, thermal physiology is correlated with climatic variables such as temperature and aridity. There is also evidence that thermoregulatory traits vary with fine-scale microclimate, but this has received less attention in endotherms. Here, we test the hypothesis that avian thermoregulation varies with microclimate and behavioural constraints in a non-passerine bird. Male and female southern yellow-billed hornbills () experience markedly different microclimates while breeding, with the female sealing herself into a tree cavity and moulting all her flight feathers during the breeding attempt, becoming entirely reliant on the male for provisioning. We examined interactions between resting metabolic rate (RMR), evaporative water loss (EWL) and core body temperature () at air temperatures () between 30°C and 52°C in male and female hornbills, and quantified evaporative cooling efficiencies and heat tolerance limits. At thermoneutral , neither RMR, EWL nor differed between sexes. At >40°C, however, RMR and EWL of females were significantly lower than those of males, by ∼13% and ∼17%, respectively, despite similar relationships between and , maximum ratio of evaporative heat loss to metabolic heat production and heat tolerance limits (∼50°C). These sex-specific differences in hornbill thermoregulation support the hypothesis that avian thermal physiology can vary within species in response to fine-scale microclimatic factors. In addition, for RMR varied substantially, with ≤2 in some individuals, supporting recent arguments that active metabolic suppression may be an underappreciated aspect of endotherm thermoregulation in the heat.
在全球范围内，热生理学与温度和干旱等气候变量相关。也有证据表明，热调节特征随小尺度微气候而变化，但在恒温动物中，这方面的研究较少。在这里，我们检验了一个假设，即鸟类的体温调节会随微观气候和非雀形目鸟类的行为限制而变化。繁殖期间，雄性和雌性南方黄嘴犀鸟经历明显不同的微气候，雌性将自己封闭在树洞中生蛋和换羽所有飞行羽毛，完全依赖雄性提供食物。我们研究了雄性和雌性犀鸟在空气温度为 30°C 至 52°C 之间休息代谢率 (RMR)、蒸发失水 (EWL) 和核心体温 () 之间的相互作用，并量化了蒸发冷却效率和耐热极限。在热中性区（），RMR、EWL 和 在性别之间没有差异。然而，在 >40°C 时，雌性的 RMR 和 EWL 显著低于雄性，分别低约 13%和 17%，尽管 和 之间的关系相似，最大蒸发散热与代谢产热比和耐热极限（约 50°C）也相似。这些在犀鸟体温调节方面的性别特异性差异支持了一个假设，即鸟类的热生理学可以在物种内随小尺度微气候因素而变化。此外，RMR 的 变化很大，有些个体的 ≤2，这支持了最近的论点，即主动代谢抑制可能是恒温动物在高温下体温调节的一个未被充分认识的方面。
