群体规模对越冬灰鹤警戒行为的影响
Effects of Group Size on Vigilance Behavior of Wintering Common Cranes Grus grus
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摘要: 2005年1—3月，在云南丽江拉市海就群体规模对越冬灰鹤(Grus grus)警戒行为的影响进行了研究。用扫描取样记录群体的规模和警戒个体的数量、用焦点取样记录群体中个体警戒行为的频次和持续时间，结果显示：灰鹤群体和个体的警戒力均随群体规模增加而降低，但集群个体数超过30只后，群体警戒力便不会再下降(P>0.05)、成体的警戒持续时间也会增加(P<0.01)；当群体规模超过50只后，成体的警戒频次也会上升(P<0.05)。推测亚成体维持低警戒的群体规模上限值要高于成体，单从警戒行为分析，20—30只个体的集群可能代表越冬灰鹤的最适群体大小。Abstract: From January to March 2005, the effects of group size on the vigilance behavior of wintering Common Cranes Grus grus were studied at Lashihai Lake, Yunnan Province, China. We used scan sampling to record the group sizes and the number of vigilant individuals in each group, and focal sampling to record the frequency and duration of individual vigilance behavior. Both the vigilance efforts of groups and individuals significantly decreased as group size increased, but when the group size exceeded 30 individuals, the decrease of group vigilance became not significant (P>0.05), and the vigilance duration of adult cranes increased (P<0.01). The vigilance frequency of adults increased (P<0.05) when the size exceeded 50 individuals. Presumably, the maximal group size allowing the lowest vigilance for juvenile cranes was larger than that for adults, and the flocks composed of 20 to 30 individuals represented the optimal group size of wintering Common Cranes by considering only the vigilance behavior. Further research should focus on the synthesized effects of various factors.
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