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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Thermoregulation in free-ranging ground woodpeckers Geocolaptes olivaceus: no evidence of torpor (2017)
Auteurs :	Ryno Kemp, Auteur ; Matthew J. Noakes, Auteur ; Andrew E. McKechnie, Auteur
Type de document :	Article
Dans :	Journal of Avian Biology (48(10) 10/2017)
Article en page(s) :	1287-1294
Langues:	Anglais
Résumé :	Heterothermic responses characterised by pronounced hypometabolism and reductions in body temperature (T-b) are one of the most effective ways in which small endotherms can offset the energetic cost of endothermic homeothermy. It remains unclear, therefore, why daily torpor and hibernation are restricted to only a subset of avian lineages. To further our understanding of the phylogenetic distribution of avian torpor, we investigated winter thermoregulation in the southern African ground woodpecker Geocolaptes olivaceus. We considered this species a good candidate for heterothermy, because it is resident year-round in mountainous regions with cold winters and reliant on small ectothermic prey. We recorded T-b patterns in free-ranging individuals and measured T-b and metabolic rates in captive individuals. Neither free-ranging nor captive woodpeckers showed any indication of daily torpor or even shallow rest-phase hypothermia. All birds maintained bimodally distributed T-b characteristic of classic endothemic homeothermy, with a mean rest-phase T-b of 37.9. +/- 0.2 degrees C and no data below 37.0 degrees C. The mean circadian amplitude of T-b was 4.2 degrees C, equivalent to approximately twice the expected value. There was some evidence of seasonal acclimatisation in T-b, with a small decrease in rest-phase T-b with the onset of the austral winter. Captive birds showed patterns of resting metabolic rate and T-b consistent with the classic model of endothermic homeothermy. The apparent absence of torpor in G. olivaceus supports the notion that, unlike the case in mammals, many avian taxa that may a priori be expected to benefit from deep heterothermy do not use it.

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