Brown-headed Cowbird (Molothrus ater) Science Article 9
From May through July, 1993-1998 and 2001, effects of Brown-headed Cowbird (Molothrus ater) parasitism on 36 Warbling Vireo (Vireo gilvus) nests were documented in southwest Colorado. Overall parasitism was 75.0% and was the major source of nest failure. Among vireo nests that were not depredated, a significantly lower proportion of parasitized nests (10.2%) than nonparasitized nests (85.7%) fledged host young.
CATHERIN P. ORTEGA AND JOSEPH C. ORTEGA, The Auk 120(3):759-764,2003