A Corsican population of blue tits (Parus caeruleus) suffers extremely high levels of infestation by two species of blow flies (genus Protocalliphora) that have been suspected to influence the life-history traits of their hosts. By quantifying the abundance of the blow fly larvae infesting each brood of this population during 2 consecutive years, we showed that the distribution of these parasites did not differ from a Poisson distribution. The intensity of blow fly parasitism (mean parasite load per infested nest) was independent of the time of breeding and the available space in the nest of their bird hosts. Moreover, the total blow fly load per nest increased significantly with the number of chicks, whereas the parasite load per chick was not linearly related to brood size.
Parental genetic similarity and offspring performance in blue tits in relation to brood size manipulation