Regulation of heat exchange across the Hornbill Beak: Functional similarities with Toucans?

 

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dc.contributor.author van De Ven, T M F N en_ZA
dc.contributor.author Martin, R O en_ZA
dc.contributor.author Vink, T J F en_ZA
dc.contributor.author McKechnie, A E en_ZA
dc.contributor.author Cunningham, S J en_ZA
dc.date.accessioned 2016-10-31T07:39:00Z
dc.date.available 2016-10-31T07:39:00Z
dc.date.issued 2016 en_ZA
dc.identifier.citation van de Ven, T. M. F. N., Martin, R. O., Vink, T. J. F., McKechnie, A. E., & Cunningham, S. J. (2016). Regulation of heat exchange across the Hornbill Beak: Functional similarities with Toucans?. PloS one, 11(5), e0154768. doi:10.1371/journal.pone.0154768 en_ZA
dc.identifier.uri http://dx.doi.org/10.1371/journal.pone.0154768 en_ZA
dc.identifier.uri http://hdl.handle.net/11427/22365
dc.description.abstract Beaks are increasingly recognised as important contributors to avian thermoregulation. Several studies supporting Allen's rule demonstrate how beak size is under strong selection related to latitude and/or air temperature (T a ). Moreover, active regulation of heat transfer from the beak has recently been demonstrated in a toucan ( Ramphastos toco , Ramphastidae), with the large beak acting as an important contributor to heat dissipation. We hypothesised that hornbills (Bucerotidae) likewise use their large beaks for non-evaporative heat dissipation, and used thermal imaging to quantify heat exchange over a range of air temperatures in eighteen desert-living Southern Yellow-billed Hornbills ( Tockus leucomelas ). We found that hornbills dissipate heat via the beak at air temperatures between 30.7°C and 41.4°C. The difference between beak surface and environmental temperatures abruptly increased when air temperature was within ~10°C below body temperature, indicating active regulation of heat loss. Maximum observed heat loss via the beak was 19.9% of total non-evaporative heat loss across the body surface. Heat loss per unit surface area via the beak more than doubled at T a > 30.7°C compared to T a < 30.7°C and at its peak dissipated 25.1 W m -2 . Maximum heat flux rate across the beak of toucans under comparable convective conditions was calculated to be as high as 61.4 W m -2 . The threshold air temperature at which toucans vasodilated their beak was lower than that of the hornbills, and thus had a larger potential for heat loss at lower air temperatures. Respiratory cooling (panting) thresholds were also lower in toucans compared to hornbills. Both beak vasodilation and panting threshold temperatures are potentially explained by differences in acclimation to environmental conditions and in the efficiency of evaporative cooling under differing environmental conditions. We speculate that non-evaporative heat dissipation may be a particularly important mechanism for animals inhabiting humid regions, such as toucans, and less critical for animals residing in more arid conditions, such as Southern Yellow-billed Hornbills. Alternatively, differences in beak morphology and hardness enforced by different diets may affect the capacity of birds to use the beak for non-evaporative heat loss. en_ZA
dc.language.iso eng en_ZA
dc.publisher Public Library of Science en_ZA
dc.rights This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. en_ZA
dc.rights.uri http://creativecommons.org/licenses/by/4.0 en_ZA
dc.source PLoS One en_ZA
dc.source.uri http://journals.plos.org/plosone en_ZA
dc.subject.other Body temperature en_ZA
dc.subject.other Surface temperature en_ZA
dc.subject.other Birds en_ZA
dc.subject.other Humidity en_ZA
dc.subject.other Mandible en_ZA
dc.subject.other Vapors en_ZA
dc.subject.other Thermocouples en_ZA
dc.subject.other Animal sexual behavior en_ZA
dc.title Regulation of heat exchange across the Hornbill Beak: Functional similarities with Toucans? en_ZA
dc.type Journal Article en_ZA
dc.rights.holder © 2016 van de Ven et al en_ZA
uct.type.publication Research en_ZA
uct.type.resource Article en_ZA
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Science en_ZA
dc.publisher.department Percy FitzPatrick Institute of African Ornithology en_ZA
uct.type.filetype Text
uct.type.filetype Image


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This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Except where otherwise noted, this item's license is described as This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.