Avian prey-dropping behavior. II. American crows and walnuts
Avian prey-dropping behavior. II. American crows and walnuts
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DOI：
10.1093/beheco/10.3.220
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发表时间：
1999-05-01
影响因子：
2.4
通讯作者：
Switzer, PV
中科院分区：
文献类型：
--
作者：
Cristol, DA;Switzer, PV
复杂而耗费精力的觅食任务应该通过自然选择来塑造，以提高效率。许多种类的鸟类通过从相当高的高度反复将猎物扔到地面上来打开硬壳猎物。在美国加州中部，城市乌鸦（短嘴乌鸦）以这种方式觅食两种核桃。正如理论模型所预测的那样，乌鸦从更高的高度扔下壳更硬的坚果，当它们落在更软的基底上时，它们从更高的高度扔下坚果。选择下降坚果的高度下降，在存在许多附近的同种，表明乌鸦是敏感的kleptoparasitism的风险时，选择下降的高度。掉落高度随着同一颗核桃的重复掉落而降低，这表明乌鸦调整了重复掉落的坚果在随后的掉落中破碎的可能性。乌鸦没有改变高度下降，根据不同的猎物的质量。当面对多种猎物类型和下降的基板，并试图盗寄生率高，乌鸦调整的高度，他们下降坚果的方式，减少盗寄生的可能性，并增加从每个坚果获得的能量。
Complex and energetically expensive foraging tasks should be shaped by natural selection to be efficient. Many species of birds open hard-shelled prey by dropping the prey repeatedly onto the ground from considerable heights. Urban-dwelling American crows (Corvus brachyrhynchos) forage in this way on two species of walnuts in central California, USA. As predicted from a theoretical model, crows dropped nuts with harder shells from greater heights and dropped them from greater heights when over softer substrates. The height selected for dropping nuts decreased in the presence of numerous nearby conspecifics, indicating that crows were sensitive to the risk of kleptoparasitism when selecting drop heights. Drop height decreased with repeated drops of the same walnut, suggesting that crows adjusted for the increasing likelihood that a repeatedly-dropped nut would break on subsequent drops. Crows did not alter height of drop in accordance with differences in the mass of the prey. When faced with multiple prey types and dropping substrates, and high rates of attempted kleptoparasitism, crows adjusted the height from which they dropped nuts in ways that decreased the likelihood of kleptoparasitism and increased the energy obtained from each nut.