Cerulean Warbler - Status Assessment

Cerulean warbler, Dendroica cerulea (Wilson), is a wood warbler in the Subfamily Parulinae of the Family Emberizidae, Order Passeriformes. No controversial or unsettled issues exist in the taxonomy of this bird. The numbers of cerulean warblers are declining at rates comparable to the most precipitous rates documented among North American birds by the cooperative Breeding Bird Survey. Recent evidence suggests that events on breeding, stopover, and wintering grounds are implicated in this decline. However, no detailed life history study of the species exists. This status assessment is an attempt to assemble what is known of the species into a form that will enable biologists in the U.S. Fish and Wildlife Service to make a decision on whether or not to propose listing of the species under the Endangered Species Act. The report will also help the Service and others establish priorities for monitoring; research; and habitat protection, restoration, and management that will conserve this species. Cerulean warbler is a small, neotropical migratory bird that weighs approximately 8-10 grams, and has relatively long, pointed wings and a short tail. All plumages have two white wing bars and white tail spots. Males have streaked backs in all plumages; females do not. Males in breeding plumage are blue above, white below, with a blueblack neck ring. Females in breeding plumage are bluish green above, white below washed with yellow, with a white or yellowish line over the eye. Young birds are similar to the adult females but greener. Cerulean warblers feed primarily on insects throughout the year. Open-cup nests are placed in the canopy of forest trees where the birds raise usually a single brood. Clutch size is usually 3-4 eggs. Adult and juvenile mortality rates are unknown. The longevity record is at least 6 years. Only 1 of 1399 banded individuals has been encountered later away from the original capture locality. Conventional wisdom about habitat for cerulean warblers is that the birds breed in large tracts of deciduous forest having large trees and an open understory. These tracts may be in upland or bottomland situations. Migratory and winter season habitats are poorly known. Cerulean warblers breed in eastern North America primarily in the Ohio and Mississippi River valleys. The range generally extends from the eastern Great Plains, north to Minnesota; east to Massachusetts; and south to North Carolina and Louisiana. During migration the birds pass through the southern U.S., across the Gulf of Mexico to the highlands of Central America, and on to South America. They winter in the lower elevations of the subtropical zone of the eastern slope of the Andes and other mountains in northern South America. Historical data on the occurrence and abundance of the species are sparse and do not permit estimation of total numbers. However, it is clear that this species was a conspicuous and abundant bird throughout the Ohio and Mississippi River valleys in the past century. Currently the birds are much less numerous in areas where formerly they were abundant. The North American Breeding Bird Survey suggests that, during the past 30 years, the population has declined at an average annual rate of approximately 4%. Summaries of the Breeding Bird Survey, Breeding Bird Census, Breeding Bird Atlas, conservation status, and other information pertinent to individual nations, states, and provinces are presented for each political division within the range of the species. Current numbers and distribution of the species are such that an adequate summary of occurrence by land ownership categories cannot be prepared, other than to state that the birds are found on public lands, industrial forest lands, and other private lands. One study found the birds more frequently on public than on other land ownerships.