How hornbills handle heat: sex-specific thermoregulation in the southern yellow-billed hornbill - PubMed (original) (raw)

. 2021 Feb 24;224(Pt 4):jeb232777.

doi: 10.1242/jeb.232777.

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How hornbills handle heat: sex-specific thermoregulation in the southern yellow-billed hornbill

Barry van Jaarsveld et al. J Exp Biol. 2021.

Abstract

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 (Tockus leucomelas) 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 (_T_b) at air temperatures (_T_a) between 30°C and 52°C in male and female hornbills, and quantified evaporative cooling efficiencies and heat tolerance limits. At thermoneutral _T_a, neither RMR, EWL nor _T_b differed between sexes. At _T_a >40°C, however, RMR and EWL of females were significantly lower than those of males, by ∼13% and ∼17%, respectively, despite similar relationships between _T_b and _T_a, 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, _Q_10 for RMR varied substantially, with _Q_10 ≤2 in some individuals, supporting recent arguments that active metabolic suppression may be an underappreciated aspect of endotherm thermoregulation in the heat.

Keywords: Avian; Heat; Microclimate; Sex-specific; Thermoregulation.

© 2021. Published by The Company of Biologists Ltd.

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Competing interestsThe authors declare no competing or financial interests.

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