Nord Andreas, Nilsson Johan F, Sandell Maria I, Nilsson Jan-Ake
Department of Animal Ecology, Lund University, 223 62, Lund, Sweden.
J Comp Physiol B. 2009 Aug;179(6):737-45. doi: 10.1007/s00360-009-0357-1. Epub 2009 Apr 8.
We evaluated biotic and abiotic predictors of rest-phase hypothermia in wintering blue tits (Cyanistes caeruleus) and also assessed how food availability influences nightly thermoregulation. On any given night, captive blue tits (with unrestricted access to food) remained largely homeothermic, whereas free-ranging birds decreased their body temperature (T(b)) by about 5 degrees C. This was not an effect of increased stress in the aviary as we found no difference in circulating corticosterone between groups. Nocturnal T(b) in free-ranging birds varied with ambient temperature, date and time. Conversely, T(b) in captive birds could not be explained by climatic or temporal factors, but differed slightly between the sexes. We argue that the degree of hypothermia is controlled predominantly by birds' ability to obtain sufficient energy reserves during the day. However, environmental factors became increasingly important for thermoregulation when resources were limited. Moreover, as birds did not enter hypothermia in captivity when food was abundant, we suggest that this strategy has associated costs and hence is avoided whenever resource levels permit.
我们评估了越冬蓝山雀（Cyanistes caeruleus）静息期低温的生物和非生物预测因素，还评估了食物可获得性如何影响夜间体温调节。在任何给定的夜晚，圈养的蓝山雀（可不受限制地获取食物）基本保持恒温，而自由放养的鸟类体温（T(b)）会降低约5摄氏度。这并非是鸟舍中压力增加所致，因为我们发现两组之间循环皮质酮并无差异。自由放养鸟类的夜间T(b)随环境温度、日期和时间而变化。相反，圈养鸟类的T(b)无法用气候或时间因素来解释，但在性别之间略有差异。我们认为，低温程度主要由鸟类在白天获取足够能量储备的能力所控制。然而，当资源有限时，环境因素对体温调节变得越来越重要。此外，由于鸟类在食物充足的圈养环境中不会进入低温状态，我们认为这种策略存在相关成本，因此只要资源水平允许就会避免采用。
