The response of Yellow warblers to Brown-headed cowbird models in Prince Edward Island

The negative impact of brown-headed cowbird parasitism (Molothrus ater) on the reproductive success of many songbirds has led to the evolution of host defensive behaviours that may reduce the chance of being parasitized. Populations of songbirds that have only recently experienced cowbird parasitism, however, may have had insufficient time to develop such behaviours. We examined the response of nesting yellow warblers (Dendroica petechia), a host species, to cowbird models on Prince Edward Island, where cowbirds have been present for less than 50 years. Yellow warblers gave more alarm calls and remained closer to their nests when presented with a cowbird model than when presented with a model of a white-throated sparrow (Zonotrichia albicollis), a nonthreatening local species. Our results suggest that yellow warblers recognize brown-headed cowbirds as greater threats to their nests and respond in a way that is similar to other populations which have been exposed to cowbirds for a much longer period of time.