Phenotypic correlates of breeding status in female carrion crows (Corvus corone corone) and hooded crows (Corvus c. cornix)

Abstract

Linear body size and plumage characters are relevant to various social and sexual aspects of bird life. In carrion crows, size is related to the individuals’ position in the dominance hierarchy which, in turn, influences the chances of acquiring a territory and of breeding. In this study, 22 osteological and plumage linear measurements in breeding and non‐breeding females are compared in two populations of the carrion crow (Corvus corone coroné) and the hooded crow (Corvus corone cornix). Breeding individuals significantly differed from non‐breeding ones in several morphological features and scored higher averages in almost all of them. Discriminant analysis revealed that breeding and non‐breeding females were separated in the multivariate space of morphological variables and furnished an efficient classification criterion of specimens. Principal component analysis indicated that the chances of becoming a breeder increase with size. Nesting for female crows is strictly correlated with fitness, since nest parasitism is likely to be rare. Hence, larger female crows of both morphs attain a higher fitness than smaller ones. Linear body measurements and, to a lesser extent, plumage characters have been shown to be highly heritable in birds. This implies that a potential evolutionary response to selection in terms of increased body size exists in the two crow populations studied which, however, might be balanced by other selective pressures acting in other parts of the life cycle of crows.

Key words:

• Linear morphological measures
• Fitness
• Breeding status
• Corvus corone corone
• Corvus corone cornix.