Abstract
Nestling birds are often parasitized while in the nest, and the parasites can have significant negative effects on the nestlings. I examined the host-parasite interactions between eastern bluebirds (Sialia sialis) and their blowfly (Protocalliphora sp.) parasites over three field seasons in a Pennsylvania bluebird population. I randomly divided broods into control and experimental groups. Control broods had natural levels of parasites, and experimental broods had all parasites removed during the nestling period. In the first part of the study, I examined the effects of blowfly parasites on nestling growth, health and survival. There was no significant effect of parasites on nestling growth and survival to fledging. Parasites significantly negatively affected blood measures of nestling health; parasitized broods were anemic compared to unparasitized broods. In addition, parasitized broods fledged significantly later than unparasitized broods. Next I examined the behavioral responses of parents and nestlings to blowfly parasites. I tested the Parental Compensation Hypothesis by determining whether parasites affected the rate of food delivery, or the type or amount of food delivered by parents to nestlings. There was no significant difference between control and experimental broods in delivery rates, or the type or amount of food delivered. I also examined the nestlings' behavioral response by recording begging vocalizations. I found no significant affect of parasites on any measures of nestling begging activity. Finally, I examined the immunological response of nestlings to blowflies by determining leukocyte counts from bloodslides. There was a significant increase in nestling leukocyte counts with increasing parasite intensities. In addition, eosinophil counts increased with increasing parasite intensities indicating that avian eosinophils respond to parasites in manner similar to mammalian eosinophils.