Durant Joël M, Landys Meta M, Handrich Yves
Department of Biology, Centre for Ecological and Evolutionary Synthesis, University of Oslo, PO Box 1066 Blindern, 0316 Oslo, Norway.
J Comp Physiol B. 2008 Jul;178(5):563-71. doi: 10.1007/s00360-007-0246-4. Epub 2008 Jan 9.
European barn owl chicks (Tyto alba) show a body mass overshoot prior to fledging that has been predicted to serve as an energy reservoir during periods of stochastic food availability. However, the composition of the mass overshoot has heretofore not been directly examined in nestlings of this or any other species displaying a body mass overshoot during growth (e.g., raptors and seabirds). To experimentally determine whether the overshoot in body mass in juvenile European barn owls (Tyto alba) may act as an energy reservoir, we compared the body composition of owl chicks raised on an ad libitum diet to those fed a restricted diet designed to eliminate the overshoot. Chicks raised on the two diets were also compared for differences in maturation of diverse functions (e.g., locomotion) and tissues (e.g., skeletal development). Contrary to expectations, our results on body composition in juvenile barn owls indicate that the mass overshoot prior to fledging is primarily comprised of an increased water compartment. Thus, we suggest that the mass overshoot in owls (and possibly in other species) does not serve as an energy reservoir but, rather, may function as an insurance against dehydration when hot in-nest conditions force chicks to rely on evaporative cooling: temperatures in barn owl nests can reach up to 43 degrees C. We found no significant differences in maturation indexes between diet treatments at the time of fledging.
欧洲仓鸮雏鸟（Tyto alba）在离巢前体重会出现超调现象，据预测，这一现象可作为在食物供应随机的时期的能量储备。然而，迄今为止，尚未直接研究过这种或其他在生长过程中出现体重超调现象的物种（例如猛禽和海鸟）雏鸟的体重超调成分。为了通过实验确定欧洲仓鸮幼鸟体重的超调是否可作为能量储备，我们将自由采食的仓鸮雏鸟的身体组成与那些喂食旨在消除超调现象的限制饮食的雏鸟进行了比较。还比较了两种饮食喂养的雏鸟在各种功能（例如运动）和组织（例如骨骼发育）成熟度方面的差异。与预期相反，我们对仓鸮幼鸟身体组成的研究结果表明，离巢前的体重超调主要由增加的水分部分组成。因此，我们认为，仓鸮（可能还有其他物种）的体重超调并非作为能量储备，而是在炎热的巢内条件迫使雏鸟依靠蒸发散热时，可能起到防止脱水的作用：仓鸮巢穴的温度可达43摄氏度。我们发现，离巢时不同饮食处理之间的成熟指数没有显著差异。
