On the importance of radiative heat exchange during nocturnal flight in birds
On the importance of radiative heat exchange during nocturnal flight in birds
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DOI：
10.1242/jeb.01964
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发表时间：
2006-01-01
影响因子：
2.8
通讯作者：
Larochelle, J
中科院分区：
文献类型：
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作者：
Léger, J;Larochelle, J
许多迁徙飞行发生在无云的夜晚，因此在天空温度通常低于当地气温20摄氏度的条件下。然后，天空就像一个辐射汇，导致暴露在天空中的物体比未暴露的物体具有更低的表面温度，因为从天空接收到的红外能量比从与空气等温的表面接收到的红外能量少。为了研究这种效应对鸟类夜间飞行过程中散热的意义，我们建立了一个风洞，该风洞具有在与飞行速度相当的空气速度（U-WIN）下独立控制壁温（T-ASK）和空气温度（T-AIR）的设施。我们用它来测量T-ASK，T-AIR和U-WIN对鸽子的羽毛和皮肤温度的影响，鸽子必须在飞行姿势中休息时消耗热负荷。结果表明，仅基于T-AIR、T-ASK和U-WIN的多元回归模型（r（2）> 0.96）可以准确地描述暴露于辐射汇的飞行和隔热羽的温度。基于这些模型的预测表明，虽然对流在热均匀环境中暴露于以飞行速度移动的空气中的羽毛的热损失中占主导地位，我们的数据还表明，将T-ASK降低到比T-AIR低20摄氏度的温度，可以使暴露的羽毛之间的温差增加至少13%从而促进热量如何通过主要的热阻损失的内部产生的热量在鸟类。虽然从我们的实验约束条件外推到大气中的自由飞行是困难的，但我们的研究结果表明，在确定T-AIR的范围时，天空温度一直是一个被忽视的因素，在T-AIR的范围内，长时间的飞行是可能的。
Many migratory flights take place during cloudless nights, thus under conditions where the sky temperature can commonly be 20 degrees C below local air temperature. The sky then acts as a radiative sink, leading objects exposed to it to have a lower surface temperature than unexposed ones because less infrared energy is received from the sky than from the surfaces that are isothermic to air. To investigate the significance of this effect for heat dissipation during nocturnal flight in birds, we built a wind tunnel with the facility to control wall temperature (T-ASK) and air temperature (T-AIR) independently at air speeds (U-WIN) comparable to flying speeds. We used it to measure the influence of T-ASK, T-AIR and U-WIN on plumage and skin temperatures in pigeons having to dissipate a thermal load while constrained at rest in a flight posture. Our results show that the temperature of the flight and insulation plumages exposed to a radiative sink can be accurately described by multiple regression models (r(2)> 0.96) based only on T-AIR, T-ASK and U-WIN. Predictions based on these models indicate that while convection dominates heat loss for a plumage exposed to air moving at flight speed in a thermally uniform environment, radiation may dominate in the presence of a radiative sink comparable to a clear sky.Our data also indicate that reducing T-ASK to a temperature 20 degrees C below T-AIR can increase the temperature difference across the exposed plumage by at least 13% and thus facilitate heat How through the main thermal resistance to the loss of internally produced heat in birds. While extrapolation from our experimentally constrained conditions to free flight in the atmosphere is difficult, our results suggest that the sky temperature has been a neglected factor in determining the range of T-AIR over which prolonged flight is possible.