Thouzeau C, Duchamp C, Handrich Y
Centre d'Ecologie et Physiologie Energétiques, associé à l'Université Louis Pasteur, Centre National de la Recherche Scientifique, 23 rue Becquerel, F-67087 Strasbourg Cedex 02, France.
Physiol Biochem Zool. 1999 Mar-Apr;72(2):170-8. doi: 10.1086/316659.
Energetic adaptation to fasting in the cold has been investigated in a nocturnal raptor, the barn owl (Tyto alba), during winter. Metabolic rate and body temperature (Tb) were monitored in captive birds, (1) after acute exposure to different ambient temperatures (Ta), and (2) during a prolonged fast in the cold (4 degrees C), to take into account the three characteristic phases of body fuel utilization that occur during a long-term but reversible fast. In postabsorptive birds, metabolic rate in the thermoneutral zone was 4. 1+/-0.1 W kg-1 and increased linearly below a lower critical temperature of 23 degrees C. Metabolic rate was 70% above basal at +4 degrees C Ta. Wet thermal conductance was 0.22 W kg-1 degrees C-1. During fasting in the cold, the mass-specific resting metabolic rate decreased by 16% during the first day (phase I) and remained constant thereafter. The amplitude of the daily rhythm in Tb was only moderately increased during phase II, with a slight lowering (0. 6 degrees C) in minimal diurnal Tb, but rose markedly in phase III with a larger drop (1.4 degrees C) in minimal diurnal Tb. Refeeding the birds ended phase III and reversed the observed changes. These results indicate that diurnal hypothermia may be used in long-term fasting barn owls and could be triggered by a threshold of body lipid depletion, according to the shift from lipid to protein fuel metabolism occurring at the phase II/phase III transition. The high cost of regulatory thermogenesis and the limited use of hypothermia during fasting may contribute to the high mortality of barn owls during winter.
在冬季，对一种夜行猛禽仓鸮（Tyto alba）在寒冷环境中禁食时的能量适应情况进行了研究。在圈养鸟类中监测了代谢率和体温（Tb），（1）在急性暴露于不同环境温度（Ta）后，以及（2）在寒冷（4摄氏度）环境中长时间禁食期间，以考虑长期但可逆禁食过程中身体燃料利用的三个特征阶段。在吸收后状态的鸟类中，热中性区的代谢率为4.1±0.1 W kg-1，在低于23摄氏度的较低临界温度时呈线性增加。在Ta为+4摄氏度时，代谢率比基础代谢率高70%。湿热传导率为0.22 W kg-1摄氏度-1。在寒冷环境中禁食期间，质量特异性静息代谢率在第一天（第一阶段）下降了16%，此后保持不变。Tb的每日节律幅度在第二阶段仅适度增加，最低日Tb略有降低（0.6摄氏度），但在第三阶段显著上升，最低日Tb下降幅度更大（1.4摄氏度）。给鸟类重新喂食结束了第三阶段并逆转了观察到的变化。这些结果表明，日间低温可能被长期禁食的仓鸮所利用，并且可能根据在第二阶段/第三阶段转变时从脂质燃料代谢向蛋白质燃料代谢的转变，由身体脂质消耗阈值触发。调节性产热的高成本以及禁食期间低温的有限利用可能导致仓鸮在冬季的高死亡率。
