This vocal yet sometimes elusive vireo, which breeds throughout the Caribbean Basin, is limited in the United States to coastal mangroves and hardwood forests of southern Florida. It resembles the closely related Red-eyed (Vireo olivaceus) and Yellow-green (V. flavoviridis) vireos in plumage, but can be distinguished from these by its black lateral throat stripe (so-called "whiskers") and browner back. Usually heard before the bird is seen, the song of this species is similar to that of the Red-eyed Vireo, but is sharper, with more abrupt pitch changes. A deliberate forager, the Black-whiskered Vireo gleans fruits and insects from the distal branches of trees and bushes, and occasionally hovers to obtain fruits. Its drab, greenish plumage and deliberate movement make it a difficult bird to observe in dense foliage.
In Florida, the Black-whiskered Vireo is generally a mangrove specialist, but throughout its extensive Caribbean range it prefers subtropical dry limestone and mesic lowland forests to mangroves. Northern populations (e.g., breeders in Florida and the Bahama Islands) are migratory, wintering in lowland forests of the northern Amazon Basin. Farther south, a few are year-round residents in Hispaniola, Puerto Rico, and several other northern Caribbean islands, while in the southern part of its range most are permanent residents. Migratory Black-whiskered Vireos return to Florida, the Bahamas, and Greater Antilles to breed in early spring. Females build a pendant cup in a forked branch of an understory tree or tall shrub. Outside of Florida, nests are frequently built higher in subtropical and tropical evergreen forests.
Where this species coexists with the Shiny Cow-bird (Molothrus bonariensis), the frequency of parasitism is usually high (>50%) and causes significant reduction in reproductive output.
Black-whiskered Vireos that remain in the Greater Antilles during the nonbreeding season move to lower elevations, and must compete for food resources with overwintering warblers. Apparently, this species partitions its foraging niche through diet and foraging location. Black-whiskered Vireos consume nearly an equal amount of fruits and insects, and they forage higher in the canopy than most other gleaning insectivores during winter.
Across its breeding range in the Caribbean, the Black-whiskered Vireo is either the only vireo on an island, or it coexists with one other vireo species. Only on Jamaica does it breed sympatrically with two endemic vireos. Under these potentially competitive situations, the Black-whiskered has broader habitat tolerances, forages higher in the canopy, and consumes more fruit and larger insects than the island endemics. Interestingly, where Black-whiskered Vireos are permanent residents in the Lesser Antilles they are the only vireo on the island, and those islands occur beyond the southern extent of where many migrant warblers winter in the Caribbean.
This widespread Caribbean songster has been the focus of a number of avian-community studies. Habitat selection has been analyzed in Florida ( Robertson 1955 ), Grand Bahama ( Emlen 1977 ), Puerto Rico ( Wiley 1988 ), Jamaica ( Lack 1976 , Cruz 1980b ), Cayman Islands ( Johnston 1975a ), and the Lesser Antilles ( Lack 1976 ). Foraging ecology has been examined in a number of studies ( Lack 1976 ; Cruz Cruz 1980a , Cruz 1987 ; Carlo 1999 ), especially in relation to niche-partitioning among wintering vireos ( Barlow 1980b ), and with wintering warblers in Puerto Rico (Terbough and Faaborg 1980b ). As Black-whiskered Vireo is a host of Shiny Cowbird, brood parasitism has been studied in Puerto Rico ( Wiley 1985a , Pérez-Rivera 1986 , Nakamura 1995 , BLW), the Dominican Republic ( Cruz et al. 1989 ), and St. Lucia ( Post et al. 1990 ) Aspects of the intriguing partial migratory status of this vireo have been illuminated by feather-chemistry analysis ( Barlow and Bortolotti 1988 ). Clearly, more study is needed in areas of life-history characteristics (outside of Puerto Rico and Jamaica), partially migratory subspecies, and the impacts of range expansion of Shiny and Brown-headed (M. ater) cowbirds into Florida.