Bautista LM, Alonso Jc, Alonso JA
Departamento de Ecología Evolutiva, Museo Nacional de Ciencias Naturales, Madrid
Anim Behav. 1998 Nov;56(5):1237-1243. doi: 10.1006/anbe.1998.0882.
Optimal foraging theory predicts that an individual should resort to intraspecific kleptoparasitism when this foraging strategy helps to maximize its intake rate. Thus aggressor and victim should be foraging at lower and higher rates, respectively, than the flock average (intake rate maximization). Independent of the maximization principle, moreover, an aggressor should attack when its intake rate falls below a threshold critical for survival, and select a victim foraging at an intake rate high enough to ensure survival (starvation risk minimization). We tested both hypotheses using 324 aggressive displacements from feeding sites observed in flocks of common cranes, Grus grus, foraging on cereal fields. Aggressors attacked cranes feeding at higher rates than average birds. The immediate consequences of a successful attack were an increase in intake rate for the aggressor and a decrease for the victim. The intake rate of the aggressor prior to the attack was lower than both the mean intake rate of the flock and the minimum intake rate necessary to cover basic metabolic needs. After displacing its victim, the intake rate of the aggressor was higher than before the attack and also higher than the average intake rate of the flock. The intake rate of the aggressor after the attack was not higher than the mean intake rate of the flock, however, when the time spent on the attack was included. We conclude that cranes used a kleptoparasitic strategy to recover from temporary reductions in feeding rate. This was particularly the case below the threshold of intake necessary for survival. Copyright 1998 The Association for the Study of Animal Behaviour.
最佳觅食理论预测，当种内偷窃寄生这种觅食策略有助于使个体的摄入率最大化时，个体会采取这种策略。因此，攻击者和受害者的觅食速率应分别低于和高于鸟群平均水平（摄入率最大化）。此外，抛开最大化原则不谈，当攻击者的摄入率降至对生存至关重要的阈值以下时，它应该发起攻击，并选择一个觅食速率高到足以确保生存的受害者（饥饿风险最小化）。我们利用在谷物田觅食的普通鹤（Grus grus）鸟群中观察到的324次从取食地点发生的攻击性驱赶行为，对这两种假设进行了检验。攻击者攻击的是觅食速率高于平均水平的鹤。成功攻击的直接后果是攻击者的摄入率增加，而受害者的摄入率降低。攻击前攻击者的摄入率低于鸟群的平均摄入率以及满足基本代谢需求所需的最低摄入率。赶走受害者后，攻击者的摄入率高于攻击前，也高于鸟群的平均摄入率。然而，当把攻击所花费的时间计算在内时，攻击后攻击者的摄入率并不高于鸟群的平均摄入率。我们得出结论，鹤采用了偷窃寄生策略来从进食速率的暂时降低中恢复过来。在生存所需的摄入阈值以下时尤其如此。版权所有1998动物行为研究协会。
