Influence of morphology on winter residence and recruitment in juvenile coal tits (Parus ater) after the post-fledging period

Abstract

We studied the role of early developed phenotypic characters associated to body size (i.e., tarsus, wing, and tail length) together with body mass in the determination of the winter residence and recruitment of juvenile coal tits (Parus ater) captured after the post-fledging period. From morphological variables and by means of multivariate analysis, we obtained an index of overall body size, an index of relative tarsus length, and an index of body condition independent of body size. Tarsus index and to a lesser extent condition index, but not overall body-size index, were associated to recruitment. The tarsus index was also positively associated with the probability of individuals becoming residents within the study area during winter, which turned out to be the key factor determining recruitment of juveniles in our coal tit population. However, effects of the tarsus index on juvenile recruitment appeared to be a complex function acting at different stages during the individual’s first winter. The tarsus index seemed to be indirectly related to recruitment by favouring winter residence in large individuals, but among resident individuals recruitment was low for very large ones, resulting in individuals of intermediate tarsus lengths having overall higher recruitment rates. The body-condition index also influenced recruitment indirectly by favouring residence in individuals with intermediate values. Our results suggest that conditions during early growth of phenotypic characters may have an influence on individual fitness extending after the post-fledging period by influencing social factors crucial to recruitment such as winter residence.