Morning Nest Arrivals in Cowbird Hosts: their Role in Aggression, Cowbird Recognition, and Host Response to Parasitism

摘要: Indigo Buntings (Passerina cyanea) nesting in old-field habitats central Missouri are parasitized at least four times as often Field Sparrows. I used model cowbirds placed near nests to test if host aggression explained this difference. Although both Sparrows and responded Brown-headed Cowbird models with significantly more chips than a Fox Sparrow (Passerella iliaca) control, only one female Bunting pair attacked the cowbird model. Because utility of recognition may depend on host's actually encountering laying cowbirds, also observed arrival hosts dawn during egg laying. Laying rarely encountered cowbirds; mean time for Cowbirds was 11.4 min before sunrise (N =8), arrived 16.7 after = 6). or about same (mean 17.4 sunrise, N =16). Most were abandoned 1992 1993, suggesting that detection nest causes desert their nests. These results suggest prevents from these hosts, but brood parasites elicits desertion by Additionally, lead underestimates parasitism frequencies, because deserted less likely be found. Nest limit efficacy defenses against especially must commute breeding areas distant communal roosts.