The North American Wood Warblers are known for their colorful beauty. The male Black-throated Blue Warbler (Dendrioca caerulescens, left) is one of the most beautiful. This species is one of the most sexually dimorphic as well — the female is not blue at all — and was not even recognized as the same species until the late 1800s. The pale “hanky” showing on the lower edge of her wing, which matches that of the male, is the only giveaway.
This eastern warbler nests in large forests in the northeastern United States and southern Canada and in higher elevations of the Appalachian Mountains. They spend the winter mostly in the West Indies, as well as along the Caribbean coast of the Yucatan, Belize, and Honduras. New techniques using a simple laboratory test of the molecular composition of feathers has revealed that Black-throated Blue Warblers from the northern part of the breeding range winter mostly in Cuba and Jamaica, and birds that nest in the Appalachians winter mostly in Hispaniola and Puerto Rico .
A common species in shade coffee ecosystems
Wintering Black-throated Blue Warblers are frequently found on coffee farms, with studies noting them using these plantations in Jamaica, Puerto Rico, the Dominican Republic, Haiti, and Chiapas, Mexico. These studies often note that Black-throated Blue Warblers are one of the most common migrants found on the farms.
While wintering in coffee farms, Black-throated Blue Warblers consume primarily small insects, many of which are coffee pests. In Jamaica, Black-throated Blues were the number one predator recorded on the dreaded coffee berry borer.
Like some other species of wintering migrants, Black-throated Blues tend to segregate themselves by sex on their wintering grounds. Males tend to be found in tall, mature forest habitat, and females in shorter, shrubby habitat. Research has shown that in the Dominican Republic, shade coffee farms had more males than females [3,5], indicating that shade coffee farms were a good substitute for tall forest habitats.
Many bird species return to the same places to nest each year, and some also return to regular wintering areas. Black-throated Blue Warblers are very faithful to their wintering sites [2,3]. In fact, they have a stronger fidelity to their winter territories than their nesting territories, making the health of the habitats on coffee farms critical to their survival . Declines in abundance of breeding populations in the southern Appalachians of over 2% a year the last two decades may be linked to severe habitat degradation in parts of the winter range, particularly Haiti  where deforestation is particularly severe.
The Black-throated Blue Warbler’s song is sometimes described as sounding like a buzzy “beer-beer-beer!” From its strong affiliation with shade fincas in the winter, we know what it really means is “coffee-coffee-coffee!”
 Rubenstein, D. R., C. P. Chamberlain, R. T. Holmes, M. P. Ayres, J. R. Waldbauer, G. R. Graves and N. C. Tuross. 2002. Linking breeding and wintering ranges of a Neotropical migrant songbird using table isotopes. Science 295: 591-593.
 Wunderle, J. M., Jr. 1995. Population characteristics of Black-throated Blue Warblers wintering in three sites in Puerto Rico. Auk 112: 931-946.
 Wunderle, J. M., Jr. and S. C. Latta. 2000. Winter site fidelity of nearctic migrants in shade coffee plantations of different sizes in the Dominican Republic. Auk 117: 596-614.
 Holmes, R. T. and T. W. Sherry. 1992. Site fidelity of migratory warblers in temperate breeding and Neotropical wintering areas: Implications for population dynamics, habitat selection, and conservation. pp. 563-575. In: J. M. Hagan III and D. W. Johnston (eds.). Ecology and Conservation of Neotropical Migrant Landbirds. Smithsonian Institution Press.
 Wunderle, J. M., Jr. and S. C. Latta. 1996. Avian abundance in sun and shade coffee plantations and remnant pine forest in the Cordillera Central, Dominican Republic. Ornithologia Neotropical 7: 19-34.
Top male Black-throated Blue Warbler by Jerry Oldenettel; bottom by Julie Craves.