Results of simulated brood parasitism on five Gray Jay (Perisoreus canadensis) nests suggest acceptance of model Brown-headed Cowbird (Molothrus ater) eggs. This finding is contrary to results of experimental parasitism on four other species of jays, also with little or no recent history of parasitism, which eject cowbird eggs. Given that Gray Jays nest in the boreal forest and earlier in the season than cowbirds initiate breeding, it may be that neither Gray Jays nor their congeners have been parasitized regularly in their evolutionary histories, which may explain acceptance of cowbird parasitism.
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Vol. 121 • No. 1