The cerulean warbler (Setophaga cerulea) is a small songbird in the family Parulidae. It is a long-distance migrant, breeding in eastern North American hardwood forests. In the non-breeding season, it winters on the eastern slope of the Andes in South America, preferring subtropical forests.
It displays strong sexual dichromatism: Adult males have cerulean blue and white upperparts, with a black necklace across the breast and black streaks on the back and flanks. Females and immature birds have bluish-green upperparts, a pale stripe over the eye, no streaking, and are yellow below. All have two white wing bars and a thin, pointed bill.
The song is a buzzed accelerating zray zray zray zray zeeee. The primary call is a buzzy, metallic zzee. Males use their songs to attract potential mates and to mark out their territory. Cerulean warblers are also capable of imitating the songs of other birds alongside their typical song. Females rarely sing, but often call when nesting. An alarm call is used to signal the arrival of a predator or another bird threatening the nest.