Nocturnal body temperature in wintering blue tits is affected by roost-site temperature and body reserves
2011
Nord, Andreas | Nilsson, Johan F. | Nilsson, J.-Å
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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