BIRD OF THE WEEK: 4/18/2014 SCIENTIFIC NAME: Setophaga caerulescens
POPULATION: 2 million
TREND: Stable
HABITAT: Deciduous woods with thick understory for breeding; dense tropical forests in winter

The Black-throated Blue Warbler's species name is the Latin adjective caerulescens, which means “turning blue.” The male is a lovely sight—a striking mix of black, blue, and white.

The male's song, which sounds like zoo-zoo-zoo-zeee, has a distinctive buzzy quality and upward inflection. It is also rather slow-paced for a warbler and often described by birders as “I'm so lazeeeeeee.”

A Visitor to ABC-supported Reserves

Unlike some eastern wood warblers, such as Cerulean and Golden-winged, the Black-throated Blue's population is stable, and ABC's work helps to keep it that way. Reserves in our International Reserve Network—now numbering more than 70—provide overwintering habitat.

Efforts to reduce threats to birds support the Black-throated Blue and many other warblers, which are frequent casualties of free-roaming cats, collisions with glass windows, wind turbines, and communication towers.

The female Black-throated Blue Warbler is distinctly different from the male, but still shows the white "handkerchief." Photo by Agami Photo Agency, Shutterstock

Variations in Black-throated Blue Warbler

While the male Black-throated Blue is vibrantly colored, the female is so nondescript that Alexander Wilson, known as the “father of American ornithology,” described it as a separate species in the 19th century. Wilson called the female bird “Pine Swamp Warbler,” and several years later, when John James Audubon painted this bird, he called it the same thing.

Despite these drastic differences in appearance (known as sexual dimorphism), both male and female Black-throated Blues have a white base on their primary feathers, forming a distinctive “pocket handkerchief” marking.

Male Black-throated Blue Warblers nesting in the Appalachian Mountains have black streaks on their backs, not solid blue like other populations, and might be a distinct subspecies.

Interestingly, on the wintering grounds, the sexes use slightly different habitats. One study in Puerto Rico showed that males were most common in forest at lower to mid-elevations, while females used shrubbier habitat at higher elevations.