Pravosudov VV, Grubb TC
Behavioral Ecology Group, Department of Zoology, The Ohio State University
Anim Behav. 1998 Jul;56(1):49-54. doi: 10.1006/anbe.1998.0739.
Fat reserves are an important energy source for animals wintering in temperate zones. Long nights, low ambient temperature and often unpredictable food all increase the probability of death from starvation, and to survive, animals carry energy reserves as fat. Based on the assumption that extra weight makes birds more vulnerable to diurnal predators, it has been hypothesized that predation risk places an upper limit on avian fat reserves. The hypothesis leads to the prediction that birds should decrease their mass in response to increased risk of predation. We tested this prediction with a resident species, the tufted titmouse, Baelophus bicolor. During a 3-day period, we presented a taxidermic mount of a sharp-shinned hawk, Accipiter striatus (predator treatment) or a mourning dove, Zenaida macroura (control treatment) to seven titmice housed individually with food ad libitum. Even though vigilance and delay in time to resume foraging were significantly higher after exposure to the hawk model, the body mass of titmice after exposure to the hawk increased rather than decreased, a result opposite to that predicted. In particular, the birds significantly increased their evening body mass and mean daily mass gain during the treatment period. Our results suggest that risk-dependent foraging appears to regulate avian body fat reserves by limiting foraging time. When food is unlimited, as in our experiment, birds may be able to obtain high energy reserves even while maintaining intense vigilance for predators, and under such conditions, the energetic costs of flying may control upper level energy reserves.Copyright 1998 The Association for the Study of Animal Behaviour.
脂肪储备是温带地区越冬动物的重要能量来源。漫长的夜晚、低温的环境以及常常难以预测的食物供应，都增加了动物因饥饿而死亡的可能性。为了生存，动物会以脂肪的形式储存能量。基于额外的体重会使鸟类更容易成为昼间捕食者猎物的假设，有人提出捕食风险对鸟类的脂肪储备设定了上限。这一假设导致了这样的预测：鸟类应该会随着捕食风险的增加而减轻体重。我们用留鸟簇山雀（Baelophus bicolor）对这一预测进行了测试。在为期3天的时间里，我们将一只条纹鹰（Accipiter striatus）的标本（捕食者处理组）或一只哀鸽（Zenaida macroura）的标本（对照组）展示给单独饲养且食物充足的7只山雀。尽管在接触鹰的标本后，山雀的警惕性以及恢复觅食的时间延迟显著增加，但接触鹰之后山雀的体重增加而非减少，这一结果与预测相反。特别是，在处理期间，这些鸟的傍晚体重和平均每日体重增加量显著增加。我们的结果表明，风险依赖型觅食似乎通过限制觅食时间来调节鸟类的体脂储备。当食物不受限时，就像在我们的实验中一样，鸟类即使在对捕食者保持高度警惕的情况下也可能获得高能量储备，在这种条件下，飞行的能量消耗可能会控制能量储备的上限。版权所有1998年动物行为研究协会。
