Individual study: Nest feathers do not reduce ectoparasite load but do affect nestling growth rate positively in tree swallows
Stephenson S., Hannon S. & Proctor H. (2009) The function of feathers in tree swallow nests: insulation or ectoparasite barrier? The Condor, 111, 479-487
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Remove ectoparasites from nests to increase survival or reproductive success
A replicated, controlled study from June-July in 2007 in 36 experimental and 19 control nestboxes in an agricultural habitat in Alberta, Canada (Stephenson et al. 2009), found that tree swallow Tachycineta bicolor nestlings subject to ectoparasite removal through feather removal and insecticide did not grow faster or fledge earlier than control nestlings. Nestlings in control nests were larger than those in nests from which feathers were removed and insecticide applied (17.5 compared to 16.2 and 16.1 g/unit time respectively). Growth rate was positively related to number of feathers in the nest. Time between hatching and fledging and number of chicks fledged did not differ (20.4, 20.8 and 20.6 days between hatching and fledgling; 5.8, 5.4 and 5.5 nestlings fledged for control, feathers removed and insecticide nests respectively). The abundance and composition of parasitic arthropods in the nest did not differ between treatments. The authors conclude that feathers did not serve as an ectoparasite barrier, though they affected nestlings’ growth rates positively.