Henderson I G, Hart P J B
Department of Zoology, University of Leicester, University Road, LE1 7RH, Leicester, UK.
Oecologia. 1991 Feb;85(4):492-497. doi: 10.1007/BF00323760.
Foraging efficiency and intraspecific competition were compared between wild adult and immature rooks Corvus frugilegus with respect to flock size. Behavioural time budgets, and observations of prey selection and prey energetic values revealed that adult rooks in large flocks (> 50 individuals) consumed smaller, less profitable prey, but allocated more time to feeding and fed at a faster rate and with greater success than adults in small flocks. By contrast, immature rooks in flocks of more than 30 individuals allocated proportionally less time to feeding, fed at a lower rate and fed with no increase in success rate than when foraging in smaller flocks. Agonistic encounters and the avoidance of adults by immature rooks appeared responsible for such inefficient foraging. Hence immature rooks showed a preference for smaller flocks (< 50 individuals) with low adult: immature ratios while adults preferred larger flocks (> 50 individuals). We discuss the possible influence of competitive disadvantages on immature rook distribution, flock composition and post-natal dispersal.
针对集群规模，比较了野生成年白嘴鸦和未成年白嘴鸦（Corvus frugilegus）的觅食效率及种内竞争情况。行为时间分配、猎物选择观察以及猎物能量值显示，大集群（> 50只个体）中的成年白嘴鸦会捕食更小、收益更低的猎物，但相比小集群中的成年白嘴鸦，它们会将更多时间用于觅食，进食速度更快且成功率更高。相比之下，超过30只个体的集群中的未成年白嘴鸦用于觅食的时间比例相对较少，进食速度较慢，且与在较小集群中觅食时相比，成功率并未提高。未成年白嘴鸦与成年白嘴鸦之间的争斗以及未成年白嘴鸦对成年白嘴鸦的回避似乎是导致觅食效率低下的原因。因此，未成年白嘴鸦表现出偏好成年与未成年比例低的较小集群（< 50只个体），而成年白嘴鸦则更喜欢较大集群（> 50只个体）。我们讨论了竞争劣势对未成年白嘴鸦分布、集群组成及出生后扩散的可能影响。
