Altricial young face two significant energetic challenges in the nest: thermoregulation and stress caused by ectoparasites. Ectoparasites feed on blood of nestlings and serve as vectors for bacterial and viral infections. Many bird species line their nests with feathers, which insulate the nest and reduce heat loss from chicks. Feathers may also affect ectoparasite numbers by serving as a parasite barrier. We tested the possible roles of nest feathers and the effects of nest parasites on the growth and survival of Tree Swallow (Tachycineta bicolor) nestlings by comparing young in control nests with those in nests from which we removed feathers and removed feathers plus used an insecticide in an attempt to reduce ecotoparasites. On the day chicks fledged, control nests had seven times more feathers in them than both categories of nests from which we removed feathers. Nestlings in control nests were larger than those in nests from which feathers were removed, and chick growth was positively related to number of feathers in the nest. Among the three categories, however, time between hatching and fledging and number of chicks fledged did not differ. Time between hatching and fledging may have been influenced by amount of rain just prior to fledging. The abundance and composition of arthropods in the nest did not differ among the categories either, suggesting that our treatments did not significantly reduce parasite numbers. Therefore, the effect of parasites on chick growth and survival remains equivocal. We concluded that feathers did not serve as an ectoparasite barrier, though they affected nestlings' growth rates positively.
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