Nestling period has been shown to be between 10 and 11 days. Both parents feed the young and remove fecal sacs. Birds reach sexual maturity and breed when 1 year old. Behavior When flying, D. cerulea makes short, direct trips between trees. Male breeders are known to be very aggressive, attacking each other in the upper canopy and grappling with their feet and bills while falling with spread wings and tail.
Males maintain territories by such agonistic behavior as well as by singing tirelessly.
It is assumed that pairs are monogamous, but information is scant. This warbler spends winters in large mixed-species flocks. Habitat Cerulean Warblers are associated in the U.S. and Canada with large, old-growth tracts of deciduous floodplain forest, a habitat that has become extremely rare in the last century. Sensitivity to fragmentation in these areas, along with strict wintering-ground requirements of primary, humid evergreen forest along a narrow band in the Andes foothills, has put the species in jeopardy. Even though they are found breeding in tracts of only 10 ha, studies suggest that large, unfragmented forested areas may be required to support viable breeding populations.