POPULATION BIOLOGY OF SWIFT (APUS-APUS) ECTOPARASITES IN RELATION TO HOST REPRODUCTIVE SUCCESS

1. We censused ectoparasite populations of adult and nestling swifts o ver the course of the host's breeding season. Nearly all of the birds were infested with chewing lice and two-thirds of the nests were infes ted with louse flies. Feather mites were observed but not quantified. 2. Lice and louse flies both showed aggregated distributions among hos ts. Louse eggs, hatched lice and adult louse flies had negative binomi al distributions, whereas the aggregated distribution of louse fly pup ae was not adequately described by negative binomial or Poisson models . 3. Transmission of lice from parents to offspring was documented. A comparison of the age structure of lice on parents and offspring indic ated that most transmission was by nymphal lice. 4. Host reproductive success and survival appeared to be independent of the number of lice or louse flies. Neither parasite correlated with the number, body mass , or date of fledging of young birds, nor with the overwinter survival of adults. We caution, however, that experimental manipulations of pa rasite load are required for a definitive test of the impact of ectopa rasites on evolutionary fitness components.