Cerulean Warbler

The Cerulean Warbler is a tiny, sky-blue wood-warbler that breeds in the canopy of mature deciduous forest across the eastern United States, with a range centered on the Appalachian and Ohio and Mississippi valley regions. It winters in foothill forest of the Andes in South America. Its bright blue upperparts and habit of foraging very high in tall trees make it a challenging species to observe well.

Breeding male upperpart feathers are a bright sky-blue with fine dark streaking on the back, while underparts are white with a narrow blue breast band across the upper chest and dark streaking along the flanks. Females lack the blue tones, showing instead pale blue-green upperparts and pale yellowish underparts without the breast band. Wings show two white wingbars in both sexes. The combination of blue upperparts, white underparts, and a narrow breast band in males is distinctive among small warblers.

Breeding males show the brightest cerulean-blue upperparts and a clean white breast crossed by a blue band. Females are considerably duller, with a pale blue-green or grayish back and yellowish wash below, lacking the breast band. A single complete molt occurs after breeding, and plumage remains fairly similar between breeding and nonbreeding seasons compared to some other warblers.

Cerulean Warblers breed in mature deciduous forest with a tall, closed canopy, particularly in the Appalachian region and the Ohio and Mississippi river valleys of the eastern United States. They winter in foothill forest along the eastern slope of the Andes in South America. Populations have shown notable declines linked to habitat fragmentation on both breeding and wintering grounds.

This species forages high in the forest canopy for insects, rarely descending to lower levels, which makes it one of the more difficult warblers to observe closely. The male's song is a buzzy, ascending series of notes. Nests are built high on horizontal branches, often well out from the trunk. It is a long-distance nocturnal migrant between eastern North American breeding grounds and Andean wintering areas.