Weight differences, brood reduction, and sibling competition among nestling Stonechats Saxicola torquata (Aves: Turdidae)

Weight differences within broods of nestling birds are commonly assumed to be the outcome of a parental strategy of selectively starving one or more offspring so as to enhance the survival of the remaining chicks. This study examined patterns of development of nestling Stonechats to reveal the significance of weight hierarchies in determining the relative growth and survival of siblings. Although Stonechat broods display obvious weight hierarchies, the results show that a low rank does not strongly influence survival within the nest, especially early in the nestling period, and in small broods. Low ranking chicks were more likely to leave the nest at lighter weights, however. A proximate mechanism for the establishment of weight hierarchies was investigated, involving competition among nestlings for advantageous positions in the nest, in which the heavier siblings were more successful.