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

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dc.contributor.authorvan De Ven, T M F Nen_ZA
dc.contributor.authorMartin, R Oen_ZA
dc.contributor.authorVink, T J Fen_ZA
dc.contributor.authorMcKechnie, A Een_ZA
dc.contributor.authorCunningham, S Jen_ZA
dc.date.accessioned2016-10-31T07:39:00Z
dc.date.available2016-10-31T07:39:00Z
dc.date.issued2016en_ZA
dc.description.abstractBeaks 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.identifier.apacitationvan 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?. <i>PLoS One</i>, http://hdl.handle.net/11427/22365en_ZA
dc.identifier.chicagocitationvan De Ven, T M F N, R O Martin, T J F Vink, A E McKechnie, and S J Cunningham "Regulation of heat exchange across the Hornbill Beak: Functional similarities with Toucans?." <i>PLoS One</i> (2016) http://hdl.handle.net/11427/22365en_ZA
dc.identifier.citationvan 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.0154768en_ZA
dc.identifier.ris TY - Journal Article AU - van De Ven, T M F N AU - Martin, R O AU - Vink, T J F AU - McKechnie, A E AU - Cunningham, S J AB - 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. DA - 2016 DB - OpenUCT DO - 10.1371/journal.pone.0154768 DP - University of Cape Town J1 - PLoS One LK - https://open.uct.ac.za PB - University of Cape Town PY - 2016 T1 - Regulation of heat exchange across the Hornbill Beak: Functional similarities with Toucans? TI - Regulation of heat exchange across the Hornbill Beak: Functional similarities with Toucans? UR - http://hdl.handle.net/11427/22365 ER - en_ZA
dc.identifier.urihttp://dx.doi.org/10.1371/journal.pone.0154768en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/22365
dc.identifier.vancouvercitationvan De Ven TMFN, Martin RO, Vink TJF, McKechnie AE, Cunningham SJ. Regulation of heat exchange across the Hornbill Beak: Functional similarities with Toucans?. PLoS One. 2016; http://hdl.handle.net/11427/22365.en_ZA
dc.language.isoengen_ZA
dc.publisherPublic Library of Scienceen_ZA
dc.publisher.departmentPercy FitzPatrick Institute of African Ornithologyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.rightsThis 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.holder© 2016 van de Ven et alen_ZA
dc.rights.urihttp://creativecommons.org/licenses/by/4.0en_ZA
dc.sourcePLoS Oneen_ZA
dc.source.urihttp://journals.plos.org/plosoneen_ZA
dc.subject.otherBody temperatureen_ZA
dc.subject.otherSurface temperatureen_ZA
dc.subject.otherBirdsen_ZA
dc.subject.otherHumidityen_ZA
dc.subject.otherMandibleen_ZA
dc.subject.otherVaporsen_ZA
dc.subject.otherThermocouplesen_ZA
dc.subject.otherAnimal sexual behavioren_ZA
dc.titleRegulation of heat exchange across the Hornbill Beak: Functional similarities with Toucans?en_ZA
dc.typeJournal Articleen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceArticleen_ZA
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