Impact of brood parasitism on nest survival parameters and seasonal fecundity of six songbird species in southeastern old-field habitat

We monitored 259 nests of six Brown-headed Cowbird (Molothrus ater) hosts w ithin old-field habitat on James Island, South Carolina during the 1997 and 1998 breeding seasons to determine the effect of parasitism on three nest- survival parameters (clutch size, hatching rate, and number of fledglings). We determined daily predation and parasitism rates, and probability of nes t abandonment after parasitism to derive an estimate of seasonal fecundity. Clutch size of parasitized nests was reduced in four host species. Brood p arasitism did not affect hatching rate in any species, and reduced the numb er of fledglings from only Blue Grosbeak (Guiraca caerulea) nests. Despite brood reduction during the nesting cycle, cowbird parasitism had little imp act on seasonal fecundity of these host species because of low parasitism i ntensity, double-brooding behavior, and hosts' ability to raise their own y oung with cowbird young.