Local sightings are reported in southeast Brazil, and very small numbers may winter in Panama and Costa Rica. Strongly sexually dimorphic, D. cerulea , however, shows little seasonal variation in plumage. Adult males are blue above and white below with dark back and side streaking and a dark breast band. Adult females have a greenish mantle, a pale yellow breast and throat, a bluish crown, and a pale supercilium. Immature males resemble adult females but show dark streaks and more blue above.
Immature females have no blue in their plumage.
In the southern United States males weighed an average of 8.35 grams and females 8.04 grams and in the northern Unites States males weighed an average of 9.28 grams and females 8.83 grams. Less frequently, the birds will sally and hover-glean to capture insects. Reproduction The Cerulean Warbler breeds in wooded swamps, mesic uplands, and wet bottomlands. The breeding season begins mid-May to early June and usually ends in July. After an 11 to 13 day female incubation period, the nestlings hatch slightly downy and altricial.