Cerulean warbler

The breeding range of the cerulean warbler extends from central Minnesota and Wisconsin in the northwest to New York’s Hudson River valley in the northeast and extending southward along the Appalachian Mountains to North Carolina and Tennessee. It winters in northwestern South America along the eastern slope of the Andes Mountains from Venezuela to Bolivia and migrates through Central American and eastern Mexico.

Breeding habitat consists of mature deciduous forests, especially in river valleys and swamps. They are typically observed higher in the tree canopy than most other species. During the winter, their habitat consists of also consists of mature forested areas with large trees.

Cerulean warblers are insectivorous. They will feed on spiders, small beetles, moths, and caterpillars, as well as other insects which they glean from leaves within tree canopies.

The breeding season for the cerulean warbler in New Jersey is between mid-April and early to mid-August. Nests are typically high (up to 88 feet), in tall trees and well out on a large branch. Nests are built by females and constructed from bark and covered with plant material such as lichens and mosses.

There is a single brood each season and between 3 to 5 eggs are laid. Incubation of the eggs is by the female and lasts about 12 days. The young are cared for by both parents and usually leave the nest after about 9 to 10 days. Cerulean warblers depart their breeding area as early as July, although some individuals may linger in their breeding area later.

The cerulean warbler has undergone a significant decline in population over the last several decades throughout portions of its range. Such declines are most likely due to habitat loss and fragmentation, with the greatest effect perhaps occurring within their winter range in South America. It is listed as a Species of Special Concern in New Jersey (not yet endangered or threatened but possibly on its way).

Forest fragmentation and loss of large trees within their breeding range eliminates suitable habitat and increases the threat of nest parasitism by brown-headed cowbirds (Molothrus ater). Preservation of large areas of intact mature deciduous forest habitat will benefit this species in both its breeding and non-breeding range. Further research on population trends, nest success, and mortality rates will be necessary to adequately manage for this species. Cowbird control and incentives to promote habitat preservation within wintering areas will also be necessary in order to conserve New Jersey’s warbler species.