For financial assistance, I am indebted to the United States Army Medical Research and Development Command which provided support for the expedition under the auspices of Grant No. DA-MD-49-193-63-G82 to the Department of Mammalogy of the American Museum. In the spring of 1964, the University of Kansas awarded me a travel grant enabling me to visit the American Museum to examine specimens during a critical part of the study.

A recent phylogenetic study of the genus Vireo, based on protein electrophoresis, shows the taxon is polyphyletic and contains four distinct groups. This contradicts the traditional classification of the genus. Johnson et al. (1988) find a group containing members of the subgenera Vireo and Lanivireo. a lone taxon containing the species V. bellii and a division of the subgenus Vireosylva into a gilvus and an olivaceus group. To test these results independently, sequence data from the mitochondrial cytochrome b (cyt-b) gene were collected from the following 9 vireos representing the three subgenera: Bell' s Vireo (Vireo belliz), Gray Vireo (k'. vicinior), Solitary Vireo (K solitarius), Black-capped Vireo (K atricapillus), White-eyed Vireo (JC griseus), Philadelphia Vireo (V. philadelphicus), Warbling Vireo (V. gilvus), Red-eyed Vireo (V. olivaceus) and Black-whiskered Vireo (V. altiloquus), and two confamilial species: Rufous-browed Peppershrike (Cyclarhis gujanensis) and Slaty-capped Shrike-Vireo (Vireolanius leucotis). For each of the above species, at least 213 homologous base pairs from the cyt-b gene were amplified using the polymerase chain reaction, and subsequently sequenced. Estimates of phylogenies were achieved through phenetic, maximum likelihood and weighted cladistic analyses. The evolutionary histories produced did not support or reject the monophyly of the genus Vireo. However, Cyclarhis was more closely related to Vireo than was Vireolanius. Two major clades were found in the genus Vireo. An eye-lined clade contained members of the subgenus Vireosylva while an eye-ringed group contained members of the subgenera Vireo and Lanivireo (including V. bellii).

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Brown-headed Cowbirds (Molothrus ater) parasitized 99 (24.4%) of 406 House Finch (Carpodacus mexicanus) nests observed at Barrie,