Behaviour varies between individuals and is often thought to be adaptive. Behaviours are predicted to vary according to the circumstances of the individual, to decrease their risk of mortality or that of their offspring, or to reduce the costs associated with certain behaviours, such as territory establishment, foraging or nestling provisioning. Two of the most important behaviours determining reproductive success, and thus having potential to be adaptive, are breeding dispersal and parental care. Individual birds should be under selection pressure to minimise the costs related to these behaviours, and likely to do so in response to aspects of habitat quality, individual quality, and their own prior experience. This study examined the relative importance of these factors upon breeding dispersal and parental care in blue tits (Cyanistes caeruleus), additionally using repeatability analysis as a novel means to indirectly assess the influence of both individual quality and habitat.
Specifically, this study explored the influence of habitat quality and individual-specific experience upon nest-site occupancy, breeding dispersal and reproductive success. It also estimated repeatability of the breeding parameters and examined the reproductive outcome of dispersal. Mixed models suggested that nestbox occupancy increased with population density but not habitat quality, and that the probability of dispersing varied by sex, with females more likely to disperse than males, and both more likely to disperse after breeding in noisier territories. Dispersal distance was not influenced by individual or habitat quality and did not influence reproductive success. Repeatability analyses suggested that habitat quality significantly influenced reproductive success. Furthermore, clutch size was strongly repeatable for females, but not males, whereas fledging success was repeatable between individual males but not females. If individual quality is consistent through their lifetime then these results suggest that female quality is important early in the breeding attempt, but that male quality exerts a stronger influence upon final fledging success.
Both males and females increased their provisioning rate to larger broods, however, the other variables influencing each sex differed. Male provisioning rates decreased as both they, and their partner, aged, but increased when a mate was retained between breeding attempts. Females increased their provisioning rate in response to their partner’s effort and provisioned at a higher rate after retaining their nest-site. However, retaining mate or nest-site did not result in higher reproductive success for either sex. The repeatability analysis suggested that females responded to the requirements of their brood, and the effort of their partner, whereas male care was less flexible. Additionally, total and male provisioning rates were repeatable for each nestbox, suggesting an influence of habitat quality. Overall, different behaviours and decisions were found to be varyingly influenced by individual, and habitat, quality and the repeatability analyses aided in assessing the relative contribution of each of these.