An Investigation of the Host Specificity of the Brown-headed Cowbird

摘要: We attempted to determine the factors associated with lack of parasitism Common Grackle (Quiscalys gyiscula> by Brown-headed Cowbird CMolothrys .a!Jll:>. investigated breeding phenology two species, responses colonialand noncolonial-nesting grackles female cowbird models, frequency artificial egg rejection grackles. incubation success eggs transferred into grackle nests, and survival rates cowbirds cross-fostered nests. By time began egg-laying at our study sites. 88.5 % all nests were beyond point successful parasitism. Grackles responded much more aggressively toward models than Fox Sparrow CPasserella lliaca> models. rejected frequently during prelay stage nesting cycle C13 reJections 32 nests> compared later stages. However, reJectlon stages Clay incubation> was virtually same as in Rothstein's original <12.4 vs. 11.3 %). A total 14 nestllngs Data collected