Small hosts infrequently disrupt laying by Brown-headed Cowbirds and Bronzed Cowbirds

摘要: Brood parasites often must overcome host defenses that may include behaviors serve other functions, such as deterrence of predators and nest attendance during laying incubation. Host use by brood also be influenced competitors in areas where more than one parasitic species occurs. We identified the degree to which behavior potential hosts affected Brown-headed Cowbirds (Molothrus ater) Bronzed (M. aeneus) at a site south Texas they co-occur. watched nests presunrise period record cowbird document visitation, laying, cowbird-host encounters, attentiveness hosts. Hosts were frequently their when cowbirds laid eggs (83% 121 watches among five species) regularly encountered (43-74% 40-77% per for cowbirds, respectively). defense infrequently interfered with rarely interacted another laying. Overall, 12% 42 attempts elicited failed, resulting either atop sat or outside cup. clearly documented relatively small can thwart parasitism cowbirds. Thus, successful should considered assessing evolution deter removal mechanisms leading abandonment. Regarding latter, presence would poor indicator some thwarted unparasitized broods reared those nests. Despite affect we did not detect an effect defense. Because most was ineffective, examined hypotheses timing attendance. Our analysis time day our data compiled from literature suggests is best predicted civil twilight (first light) rather sunrise.