HABITAT AND MICROHABITAT FEATURES ASSOCIATED WITH COWBIRD PARASITISM IN 2 FOREST EDGE COWBIRD HOSTS

I examined the relationship of habitat and nest microhabitat features of Field Sparrows (Spizella pusilla) and Indigo Buntings (Passerina cy anen) to brood parasitism by the Brown-headed Cowbird (Molothrus ater) in central Missouri. In old field habitats, Indigo Buntings were more frequently parasitized than Field Sparrows, but Indigo Buntings nesti ng in forested habitat were parasitized at higher frequencies than bun tings in old fields. Logistic regression models showed that nest conce alment best explained parasitism for all Indigo Buntings and field-nes ting Indigo Buntings, with poorly concealed nests more likely to be pa rasitized. However, side concealment was not related to parasitism for heavily-parasitized Indigo Buntings in forested habitats. Microhabita t variables did not explain parasitism at Field Sparrow nests, but the ir nests were lower and better concealed than field-nesting Indigo Bun tings. Results suggest that nest microhabitat features may influence p robability of parasitism, but species and habitat characteristics may override microhabitat in explaining frequency of parasitism.