Avian thermoregulation in the heat: evaporative cooling in five Australian passerines reveals within-order biogeographic variation in heat tolerance

McKechnie, Andrew E.; Gerson, Alexander R.; McWhorter, Todd J.; Smith, Eric Krabbe; Talbot, William A.; Wolf, Blair O.

doi:10.1242/jeb.155507

Cited by 64 publications

(136 citation statements)

References 38 publications

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“…This suggests they did not work as hard as control parents, because previous studies of blue tits demonstrate that adult mass loss increases when workload is higher or experimentally increased (Nur, ). In our study, it is possible that energy expenditure was lower in feather‐clipped birds because they were less affected by the metabolic cost of panting (McKechnie et al, ; Whitfield et al, ) during recovery, and so could maintain body mass to a larger extent than control birds (cf. du Plessis et al, ).…”

Section: Discussionmentioning

confidence: 79%

“…Simmons, Lott, & May, ). This might have increased self‐maintenance costs in the control treatment, because panting is the energetically most expensive method of evaporative cooling (McKechnie et al, ; Whitfield, Smit, McKechnie, & Wolf, ) and is largely incompatible with efficient self‐foraging (du Plessis, Martin, Hockey, Cunningham, & Ridley, ). This could explain why, in line with the HDL theory, control birds sired offspring that were structurally smaller (Figure b), and sometimes lighter (Figure a), than those of clipped birds.…”

Section: Discussionmentioning

confidence: 99%

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Heat dissipation rate constrains reproductive investment in a wild bird

Nord

Nilsson

2018

Functional Ecology

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The “heat dissipation limit” theory (HDL) posits that animals with higher capacity to dissipate metabolic heat can increase reproductive investment. This theory remains untested in the wild. We recently showed that increased workload in a small bird causally relates to maximum body temperature. Here, we have expanded this approach by experimentally facilitating sensible heat transfer rate in nestling‐feeding blue tits—a small bird with high resting‐ and work‐induced body temperatures—through removal of ventral plumage. Feather‐clipped parents did not increase work rate but sired larger, and sometimes heavier, nestlings while maintaining lower body temperature and losing less body mass than controls. Thus, when relieved of the demands to dissipate metabolic heat, parents could invest more into both current (nestling condition) and future (self‐maintenance) reproduction. In accordance with the HDL theory, we conclude that constraints on heat dissipation rate could be a potent mediator of life‐history trade‐offs in wild animals. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13243/suppinfo is available for this article.

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Section: Discussionmentioning

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Heat dissipation rate constrains reproductive investment in a wild bird

Nord

Nilsson

2018

Functional Ecology

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“…Data for 32 of the species included in this study were previously published (McKechnie et al, ; McKechnie, Smit et al, ; McKechnie, Whitfield et al, ; McWhorter et al, ; Smit et al, ; Smith, O'Neill, Gerson, McKechnie, & Wolf, ; Smith et al, ; Talbot, Gerson, Smith, McKechnie, & Wolf, ; Talbot, McWhorter, Gerson, McKechnie, & Wolf, ; Whitfield et al, ) see Table S2), whereas the remaining species (red‐billed buffalo‐weaver , Bubalornis niger ) has not been published elsewhere. The published studies detail the conditions of capture, holding and how temperature trials were performed, which all followed similar protocols.…”

Section: Methodsmentioning

confidence: 99%

The functional significance of facultative hyperthermia varies with body size and phylogeny in birds

et al. 2019

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Facultative hyperthermia, the elevation of body temperature above normothermic levels, during heat exposure, importantly affects the water economy and heat balance of terrestrial endotherms. We currently lack a mechanistic understanding of the benefits hyperthermia provides for avian taxa. Facultative hyperthermia has been proposed to minimize rates of water loss via three distinct mechanisms: M1) by maintaining body temperature (Tb) above environmental temperatures (Te), heat can be lost non‐evaporatively, saving water; M2) by minimizing the thermal gradient when Te > Tb, environmental heat gain and evaporative water loss rates are reduced; and M3) by storing heat via increases in Tb which reduces evaporative heat loss demands and conserves water. Although individuals may benefit from all three mechanisms during heat exposure, the relative importance of each mechanism has not been quantified among species that differ in their body size, heat tolerance and mechanisms of evaporative heat dissipation. We measured resting metabolism, evaporative water loss and real‐time Tb from 33 species of birds representing nine orders ranging in mass from 8 to 300 g and estimated the water savings associated with each proposed mechanism. We show that facultative hyperthermia varies in its benefits among species. Small songbirds with comparatively low evaporative cooling capacities benefit most from (M1), and hyperthermia maintains a thermal gradient that allows non‐evaporative heat losses. Other species benefited most from (M2) minimizing evaporative losses via a reduced thermal gradient for heat gain at high Te. We found that (M3), heat storage, only improved the water economy of the sandgrouse, providing little benefit to other species. We propose that differences in the frequency and magnitude of hyperthermia will drive taxon‐specific differences in temperature sensitivity of tissues and enzymes and that the evolution of thermoregulatory mechanisms of evaporative heat dissipation may contribute to differences in basal metabolic rate among avian orders. Understanding the mechanistic basis of heat tolerance is essential to advance our understanding of the ecology of birds living in hot environments that are warming rapidly, where extreme heat events are already re‐structuring avian communities. A plain language summary is available for this article.

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“…2a), and weather records show that birds may be exposed to up to 8 consecutive days of such conditions. Birds at our temperate study site are not acclimatized to very hot conditions so mass loss associated with repeated exposure to temperatures between 30 and 35°C is perhaps not surprising, particularly given recent evidence that temperature thresholds for the onset of panting and heat stress vary among species [30,57,62]. Smit and colleagues [30] showed that among 30 species of arid zone birds in South Africa the HD50 values for panting ranged between 31.3-46.0.°C (mean 39.3°C).…”

Section: Spring and Summermentioning

confidence: 99%

Associations between changing climate and body condition over decades in two southern hemisphere passerine birds

Gardner

Rowley

Rebeira³

et al. 2018

Clim Chang Responses

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Background: Climate change presents considerable challenges for endotherms because they must maintain high, relatively constant body temperatures across a range of environmental conditions to ensure survival and optimise performance. Individuals exposed to changing weather must manage energy and water allocation to maintain thermal homeostasis, with consequences for body condition, and hence there is potential for selection because body condition is strongly linked to fitness. Understanding how weather drives changes in body condition is therefore fundamental to understanding how fitness is affected by climate change. Here we test for associations between weather and body condition and how this changes over time, in two co-existing species of small insectivorous passerines, the red-winged fairy-wren, Malurus elegans and white-browed scrubwren, Sericornis frontalis, that have been the subject of a ringing study for 39 years in temperate south-western Australia. The study populations have experienced increases in minimum temperatures in winter and summer as well as decreases in the frequencies of days with thermal minima < 5°C, but the summer climate remains relatively mild with few days experiencing thermal maxima > 35°C. Although, warming temperatures may reduce thermoregulatory costs, repeated exposure to hot conditions has been shown to have negative effects on body condition. Thus, we predict that the reduction over time in daily minima < 5°C, along with the influence of increased maximum and minimum temperatures in summer and winter, will have positive effects on body condition. Results: In accordance with thermoregulatory predictions, colder daily minima in the range 1-19°C prior to capture were associated with reduced body condition in winter in both species. Furthermore, in summer, in fairy-wrens but not scrubwrens, warmer daily maxima were associated with increasing body condition, and repeated exposure to temperatures > 30°C over consecutive days was negatively associated with body condition. Body condition increased over the 39 years of the study for fairy-wrens but there was no change in scrubwrens, which is consistent with observed within-season associations between body condition and weather, and the change in climate over time.

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Avian thermoregulation in the heat: evaporative cooling in five Australian passerines reveals within-order biogeographic variation in heat tolerance

Cited by 64 publications

References 38 publications

Heat dissipation rate constrains reproductive investment in a wild bird

Heat dissipation rate constrains reproductive investment in a wild bird

The functional significance of facultative hyperthermia varies with body size and phylogeny in birds

Associations between changing climate and body condition over decades in two southern hemisphere passerine birds

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