Innes Cuthill and Jonathan Wright
Recent theoretical and experimental studies appear to provide a comprehensive explanation for the evolutionary, and short-term, stability of biparental care in birds. However, much of the intraspecific variation in the absolute and relative contribution by the male and female remains to be explained. Most studies of the natural variation across pairs reveal positive correlations between the level of male and female nest defence or brood provisioning, but some species show negative relations, or between-season variability in the direction of the relationship. This study examines the determinants of male and female provisioning rate in monogamous European starlings (Sturnus vulgaris), in terms of the patterns of male display, pairing patterns, laying phenology and clutch attributes. There was assortative pairing by body size and, controlling for female body size, larger males attracted relatively fecund mates. Males that sang relatively more, controlling for these body size effects, were paired with females that laid earlier. Female nest provisioning rates to experimentally standardized broods were positively correlated with female size, but male provisioning rates were unrelated to either song or any other attributes of themselves or their mates.