Presence of Wood Thrushes at a Nest Does Not Deter Parasitism by Brown-headed Cowbirds

Abstract

Abstract There is scant information on whether Wood Thrushes (Hylocichla mustelina) are present at nests when Brown-headed Cowbirds (Molothrus ater) come to lay their eggs. We used miniature digital video cameras to document 10 visitations by cowbirds to five Wood Thrush nests. Cowbirds visited Wood Thrush nests on six occasions when host females were absent and aggressively approached incubating females on four other visits. Parental nest defense did not appear to be an effective deterrent to a challenge by a cowbird. Wood Thrushes were more tolerant of cameras early in the nesting season than after mid-June when they were more likely to accept the presence of cameras if they were gradually moved closer to nests over a period of several days.