Ectoparasites, nestling growth, parental feeding rates, and begging intensity of tree swallows

Abstract

Many studies fail to show relationships between ectoparasite loads and nestling growth rates. One explanation is that parent birds increase feeding rates to compensate for nestling energetic losses to ectoparasites. Nestling begging behaviours could signal need to parents. Accordingly, we tested whether higher flea and blow fly loads in tree swallow (Tachycineta bicolor) nests were associated with smaller nestlings, higher parental feeding rates, and increased nestling begging intensity. The study area was the Gaspereau Valley of Nova Scotia, Canada. When nestlings were 10 days old, parental feeding rates and nestling begging intensity were measured with tape recorders. At 13 days of age, nestlings were weighed and measured. Within 2 days of fledging, nest material was removed from nest boxes and enumerated for adult fleas and blow fly pupae. After including brood size and date of first egg as covariates in general linear models, no significant relationships were found between ectoparasite loads and nestling size, parental feeding rate, or nestling begging intensity. Our results suggest that nestling tree swallows were able to buffer the effects of naturally occurring ectoparasite loads without significant help from their parents. Low levels of virulence may have resulted from relatively benign weather during the study, low numbers of ectoparasites, selection on ectoparasites to avoid killing their hosts, and host defences.