Ellsworth EA, Belthoff JR
Department of Biology and Raptor Research Center, Boise State University
Anim Behav. 1999 Apr;57(4):883-892. doi: 10.1006/anbe.1998.1050.
Variation in timing and distance of dispersal movements of juvenile birds may result from differences in competitive ability. Dispersal by low-ranking juveniles may be initiated before dominants if the latter force subordinate siblings from natal areas. Conversely, when vacant territories are limited and are acquired on a first-come first-served basis, selection could operate on young to disperse as early as possible. In this case, dominant individuals with priority of access to resources in the natal area will mature more quickly and are expected to disperse first. If costs of dispersal increase with dispersal distance, dominant juveniles are expected to disperse shorter distances. Alternately, if there are advantages to long-distance dispersal, then dominants, which are in better condition, should disperse further than subordinates. We examined effects of social rank on the timing and distance (to wintering area) of dispersal movements by juvenile western screech-owls, Otus kennicottii, in southwestern Idaho. Based on observations of aggressive interactions made using video cameras attached to nestboxes, we assigned dominance ranks to nestlings within nine broods. We radiotracked young throughout the postfledging period to determine order of dispersal, and we located them after leaving their natal areas to determine distances to apparent overwintering areas. In six of seven broods, for which dispersal information could be recorded, the most dominant juvenile dispersed first. Moreover, in five of seven broods, the least dominant individual was the last individual to disperse, and the order of dispersal matched the dominance hierarchy in four of seven broods. In contrast, social status did not affect postfledging dispersal distance. We conclude that social dominance relationships influenced the timing of dispersal in juvenile western screech-owls but not distance travelled to overwinter sites. Copyright 1999 The Association for the Study of Animal Behaviour.
幼鸟扩散运动的时间和距离变化可能源于竞争能力的差异。如果优势个体将从属的同胞赶出出生地，那么低等级幼鸟可能会比优势个体更早开始扩散。相反，当空的领地有限且按先来先得的原则获取时，选择可能会促使幼鸟尽早扩散。在这种情况下，在出生地优先获取资源的优势个体将更快成熟，并预计会最先扩散。如果扩散成本随着扩散距离的增加而增加，那么优势幼鸟预计会扩散较短的距离。或者，如果长距离扩散有优势，那么状况更好的优势个体应该比从属个体扩散得更远。我们研究了社会等级对爱达荷州西南部的西部鸣角鸮（Otus kennicottii）幼鸟扩散运动的时间和距离（到越冬地）的影响。基于使用安装在巢箱上的摄像机对攻击性行为的观察，我们给九个巢中的雏鸟分配了优势等级。我们在整个离巢期对幼鸟进行无线电跟踪以确定扩散顺序，并在它们离开出生地后定位它们以确定到明显越冬地的距离。在七个能记录扩散信息的巢中，有六个巢中最具优势的幼鸟最先扩散。此外，在七个巢中有五个巢中，最不具优势的个体是最后一个扩散的，并且在七个巢中有四个巢的扩散顺序与优势等级一致。相比之下，社会地位并不影响离巢后的扩散距离。我们得出结论，社会优势关系影响了西部鸣角鸮幼鸟的扩散时间，但不影响到越冬地点的扩散距离。版权所有1999动物行为研究协会。
