Effects of ectoparasites on seasonal variation in quality of nestling Tree Swallows (Tachycineta bicolor)
Abstract:Reproductive success often declines with breeding date in diverse taxa, including temperate-nesting bird species. The date hypothesis predicts that seasonally deteriorating environmental quality drives this pattern. While mechanisms are not fully understood, a seasonal increase in parasitism may contribute to the declining quality of nestlings hatched later in the season. We examined the effect of ectoparasites on seasonal variation in indices of nestling quality and survival in Tree Swallows (Tachycineta bicolor (Vieillot, 1808)) at breeding sites in British Columbia (PG) and Saskatchewan (SDNRA). In a parasite removal experiment, we detected no seasonal trend in flea abundance and, contrary to expectation, there were fewer blow flies in nests of late breeders. Negative effects of parasites on nestlings were documented at PG, where lengths of primary feather and head–bill were affected. Parental, rather than environmental, quality had the greatest effect on reproductive success at PG, as nestling survival declined seasonally regardless of treatment and despite seasonally increasing food biomass. Nestlings in control (i.e., parasitized) nests at SDNRA had elevated feather corticosterone levels, but no other effects of parasites were detected possibly because parent birds were of higher quality or parents and offspring had greater access to food such that nestlings were capable of coping with parasite-related challenges.
Keywords: PHA test; Tachycineta bicolor; Tree Swallow; corticostérone dans les plumes; croissance des oisillons; date hypothesis; feather corticosterone; hirondelle bicolore; hypothèse de la date; hypothèse de la qualité; insecticide; nest parasites; nestling growth; nestling size; parasites du nid; quality hypothesis; taille des oisillons; test à la PHA
Document Type: Research Article
Affiliations: 1: Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK S7N 5E2, Canada. 2: Ecosystem Science and Management Program, University of Northern British Columbia, 3333 University Way, Prince George, BC V2N 4Z9, Canada. 3: Prairie and Northern Wildlife Research Centre, Environment Canada, 115 Perimeter Road, Saskatoon, SK S7N 0X4, Canada; Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, SK S7N 5E2, Canada.
Publication date: January 1, 2014
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