Abstract
Birds commonly use rest-phase hypothermia, a controlled reduction of body temperature (T b), to conserve energy during times of high metabolic demands. We assessed the flexibility of this heterothermic strategy by increasing roost-site temperature and recording the subsequent T b changes in wintering blue tits (Cyanistes caeruleus L.), assuming that blue tits would respond to treatment by increasing T b. We found that birds increased T b when roost-site temperature was increased, but only at low ambient temperatures. Moreover, birds with larger fat reserves regulated T b at higher levels than birds carrying less fat. This result implies that a roosting blue tit maintains its T b at the highest affordable level, as determined by the interacting effect of ecophysiological costs associated with rest-phase hypothermia and energy reserves, in order to minimize potential fitness costs associated with a low T b.
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Acknowledgments
We thank R. Mark Brigham and Lars Råberg as well as the editor and two anonymous reviewers for helpful comments on a previous version of the manuscript. This study was supported by grants from the Swedish Research Council (to J.-Å.N.) and the Längman Cultural Foundation (to A.N.).
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Communicated by Esa Lehikoinen.
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Nord, A., Nilsson, J.F. & Nilsson, JÅ. Nocturnal body temperature in wintering blue tits is affected by roost-site temperature and body reserves. Oecologia 167, 21–25 (2011). https://doi.org/10.1007/s00442-011-1972-6
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DOI: https://doi.org/10.1007/s00442-011-1972-6