ARE AVIAN ECTOPARASITES MORE NUMEROUS IN NEST BOXES WITH OLD NEST MATERIAL

Researchers may reduce the numbers of haematophagous ectoparasites in nest boxes of cavity-nesting birds by removing old nests from boxes an d, as a result, eliminate an important selective pressure that could i nfluence the results from nest-box studies of birds. We recorded the n umbers of parasites in tree swallow (Tachycineta bicolor) boxes in whi ch we manipulated the presence, amount, and quality of old nests. Bird fleas (Ceratophyllus idius) were more numerous in boxes with old nest s, and there was a positive correlation between nest volume and flea n umbers. In one year, there was a positive association between fowl mit e (Ornithonyssus sylviarum) numbers and nest volume; otherwise, fowl m ites and blow flies (Protocalliphora sialia) were equally numerous in all nest types. We conclude that ectoparasites whose over-winter survi val depends on old nests are more numerous in boxes with old nests, wh ereas parasites whose over-winter survival is independent of old nests infect nest sites randomly. Also, reinfection and nest microclimate l ikely contributed to variance in parasite numbers between nest types a nd years, respectively. We recommend caution when speculating about th e possible effects of cleaning boxes on parasites that occur in nests because different species of parasites are not influenced similarly by old nests.