Cerulean Warbler

The Cerulean Warbler is a small, sky-blue jewel of the deciduous forest canopy, its bright azure upperparts and clean white underparts making adult males one of the most striking warblers in North America. A narrow dark blue-black band crosses the upper breast, and the flanks show fine dark streaking, with two white wingbars adding further contrast.

Females are far less vivid, showing a blue-green tinge to the upperparts and pale yellowish-white underparts with a pale eyebrow stripe, but they retain the wingbars and generally similar shape. The species forages almost entirely high in the canopy, making it a challenging bird to see well despite its bright color.

Key field marks

• Male: sky-blue upperparts, white underparts, thin dark breast band, streaked flanks, two white wingbars
• Female: blue-green upperparts, pale yellow-white underparts, pale eyebrow stripe, wingbars
• Small size and a habit of staying very high in the canopy

Similar species

Black-throated Blue Warbler male is a deeper blue with a solid black face/throat and white underparts, quite different from Cerulean's breast band and paler blue tone. Female Ceruleans can suggest female Northern Parula but lack the parula's yellow-green back patch and bicolored bill.

Cerulean Warblers breed in the canopy of mature deciduous forest across the eastern and midwestern United States, with a strong association with large tracts of bottomland and floodplain forest as well as mature upland hardwoods, particularly in the Appalachian and Ohio/Mississippi River valley regions.

They winter in the foothill forests of the Andes in northern South America, often in shade-grown coffee plantations and adjacent forest, habitat that is itself under significant pressure from conversion to sun-grown agriculture.

Behavior and voice

Cerulean Warblers forage almost exclusively high in the canopy, gleaning insects from leaves and twigs, and their small size and habit of staying near the treetops make them difficult to observe well even when singing nearby.

The song is a buzzy, accelerating series of notes that ends in a distinctive upslurred buzz, often rendered as "zray-zray-zray-zray-zeeeeee."

Nesting

The nest is built high in the canopy on a horizontal branch, often 10 meters (over 30 feet) or more above the ground, made of bark strips, grass, and spider silk. Clutches typically contain 3-4 eggs. The species is classified as Near Threatened, with one of the steepest population declines of any North American warbler, driven by loss of large mature forest tracts on the breeding grounds and Andean forest on the wintering grounds.