Vireo Cousins Coexist on Yucatan Peninsula
White-eyed vireos breed in eastern North America. But from October to April they range from Mexico to Central America and the Caribbean.
On the Yucatan Peninsula, they invade the year-round range of the resident Yucatan vireo. The species resemble each other. In fact, early ornithologists considered them to be the same species. But the white-eyed is a little larger with a somewhat longer tail and wing: perhaps these are helpful for their long migrations.
So, we've got two species occupying the same general area for much of the year. How do they get along?
Well, they don't fight, much. They each defend a territory, but when scientists played recorded calls they reacted much more forcefully to their own species than to the other.
They do segregate themselves. White-eyed vireos move into the forests while the Yucatan vireos inhabit the shrubby overgrown fields, pastures, and forest edges. Even during the summer, when the white-eyed vireos are gone, the Yucatans stay put in their shrubby environs.
Within their respective habitats they do pretty much the same thing. Scientists watched their activities, and they spend about the same amount of time foraging, hopping, and doing other activities. White-eyed vireos tend to do these activities higher up in the vegetation, but this seems reasonable given that they live in the forest.
But there is one difference between the two species. White-eyed vireos eat a lot more fruit, specifically from the gumbo-limbo tree (Bursera simaruba). Gumbo-limbo fruits throughout the winter and white-eyed vireos will chase off any vireo, including its Yucatan cousins, trying to sneak a bite.
This article summarizes the information in this scientific paper:
Greenberg, Russell S. 1993. Frugivory and coexistence in a resident and migratory vireo on the Yucatan Peninsula. The Condor, 95: 990-999.