Experimental evidence that hyperthermia limits offspring provisioning in a temperate-breeding bird.

Simon Tapper,Gary Burness,Joseph J Nocera

doi:10.1098/rsos.201589

Simon Tapper, Gary Burness + Show 1 more

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https://doi.org/10.1098/rsos.201589

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Abstract

In many vertebrates, parental care can require long bouts of daily exercise that can span several weeks. Exercise, especially in the heat, raises body temperature, and can lead to hyperthermia. Typical strategies for regulating body temperature during endurance exercise include modifying performance to avoid hyperthermia (anticipatory regulation) and allowing body temperature to rise above normothermic levels for brief periods of time (facultative hyperthermia). Facultative hyperthermia is commonly employed by desert birds to economize on water, but this strategy may also be important for chick-rearing birds to avoid reducing offspring provisioning when thermoregulatory demands are high. In this study, we tested how chick-rearing birds balance their own body temperature against the need to provision dependent offspring. We experimentally increased the heat dissipation capacity of breeding female tree swallows (Tachycineta bicolor) by trimming their ventral feathers and remotely monitored provisioning rates, body temperature and the probability of hyperthermia. Birds with an experimentally increased capacity to dissipate heat (i.e. trimmed treatment) maintained higher feeding rates than controls at high ambient temperatures (greater than or equal to 25°C), while maintaining lower body temperatures. However, at the highest temperatures (greater than or equal to 25°C), trimmed individuals became hyperthermic. These results provide evidence that chick-rearing tree swallows use both anticipatory regulation and facultative hyperthermia during endurance performance. With rising global temperatures, individuals may need to increase their frequency of facultative hyperthermia to maintain nestling provisioning, and thereby maximize reproductive success.

Highlights

In many vertebrates, parental care can require long bouts of daily exercise that can span several weeks
Facultative hyperthermia is commonly employed by desert birds to economize on water, but this strategy may be important for chick-rearing birds to avoid reducing offspring provisioning when thermoregulatory demands are high
Facultative hyperthermia is commonly reported among desert birds, it could presumably be employed by non-desert avian species during periods requiring high thermoregulatory demands, such as during running and flying [5,6,26]

Summary

Introduction

Parental care can require long bouts of daily exercise that can span several weeks. In non-human endotherms, experimental exposure to high ambient temperatures reduces flight time in birds [5,6] and running duration in mammals [7,8] These declines in performance are presumed to be evolutionarily adaptive, preventing dangerously high increases in body temperature (Tb) that occur from increases in metabolic production during exercise [9]. In contrast to anticipatory regulation, animals may, allow their Tb to rise in the short term by passively storing heat in body tissues This strategy of facultative hyperthermia is employed by a number of species [2,20,21,22,23] and in different contexts. Facultative hyperthermia is commonly reported among desert birds, it could presumably be employed by non-desert avian species during periods requiring high thermoregulatory demands, such as during running and flying [5,6,26]

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