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Abstract

While parasites have long been documented, the large fitness cost to their hosts has only recently been addressed via studies of ecology and evolution. Large fitness costs apply to altricial nestlings confined to the nest and completely dependent on parental care. These costs are often passed on to their parents and can either be allayed or magnified through adjustments in parental behavior. My study employs manipulation of nest parasite loads and direct visual observation to assess how ectoparasitism (external parasites) by mites in nests of the North American barn swallow (Hirundo rustica erythrogaster) affects provisioning (feeding) behavior of parents. This study addresses the question of how provisioning rates are changing not only in response to ectoparasite intensity (number of parasites present), but also how parental responses differ across the nestling period (time nestlings occupy the nest) and between sexes. Early in the nestling period (Day 7), female provisioning rates decreased as parasite load increased, with no response by males. However, later in the nestling period (Day 13), males increased provisioning rates for parasitized nests, while females did not. These findings suggest that not only do parasites affect provisioning, but that responses are dynamic and change over the nestling period.