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

Many studies fail to show relationships between ectoparasite loads and nest ling growth rates. One explanation is that parent birds increase feeding ra tes to compensate for nestling energetic losses to ectoparasites. Nestling begging behaviours could signal need to parents. Accordingly, we tested whe ther higher flea and blow fly loads in tree swallow (Tachycineta bicolor) n ests 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 f eeding rates and nestling begging intensity were measured with tape recorde rs. At 13 days of age, nestlings were weighed and measured. Within 2 days o f fledging, nest material was removed from nest boxes and enumerated for ad ult fleas and blow fly pupae. After including brood size and date of first egg as covariates in general linear models, no significant relationships we re found between ectoparasite loads and nestling size, parental feeding rat e, or nestling begging intensity. Our results suggest that nestling tree sw allows 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 numb ers of ectoparasites, selection on ectoparasites to avoid killing their hos ts, and host defences.