Responses of Five Host Species to Cowbird Parasitism

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Abstract
Responsers of the Red-eyed Vireo (Vireo olivaceus), Yellow Warbler (Dendroica petechia), Northern Cardinal (Cardinalis cardinalis), Chipping Sparrow (Spizella passerina), and Song Sparrow (Melospiza melodia) to Brown-headed Cowbird (Molothrus ater) parasitism were determined from nest records compiled at the Ontario Nest Record Scheme. Nest desertion was the prinicipal mode of rejection of cowbird eggs. The Yellow Warbler [Canada] also rejected parasite eggs by burying clutches under a second nest bottom. The probability of rejection did not vary during the breeding season or between multiply- and slightly-parasitized pairs. Possible stimuli used by hosts to recognize parasitism are discussed.