CERULEAN WARBLER

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CERULEAN WARBLER

Dendroica cerulea

The cerulean warbler is a light blue bird trimmed with black and white. This warbler lives in mature deciduous forests, often in floodplains. They have declined in number due to the destruction of bottomland forests. The species is listed as a WATCH LIST SPECIES by the Missouri Department of Conservation.

Identification

The cerulean warbler is 4 to 4.5 inches long, has a wingspan of 7.5 to 8 inches and an average weight of 3.2 ounces. Females are slightly smaller than males.

Males are azure blue on the back and white on the belly. An identifying mark is a dark blue or black line across the throat. They have dark streaking on the flanks and back. Females are dull grey-blue above with a yellowish wash below. Both sexes have two white wingbars.

Juveniles are brownish-gray above, with a pale center crown stripe and entirely white underparts. Cerulean warblers molt into an adult plumage prior to the breeding season following their hatching year.

Because cerulean warblers often remain concealed in foliage high in the forest canopy, they are usually best identified by their buzzy calls, which rise in pitch at the end.

For a technical description of this animal, refer to:

Robbins, C.S., B. Bruun, and H.S. Zim. 1983. A Guide to Field Identification: Birds of North America. Western Publishing Company. New York, NY. 360 pp.

Life History

Cerulean warblers are migratory, insectivorous songbirds. They pick small insects from tree leaves and occasionally catch flying insects.

They arrive in North America in mid-April. Nesting is initiated soon after arrival. Their compact nest is composed of shredded bark covered with gray plant material such as lichens and mosses. The shallow nest is lined with mosses. Nests are 3 to 3.5 inches in diameter and are typically constructed at a height of 15 to 90 feet above the ground and 5 to 20 feet out on a branch. The clutch of 3 to 5 eggs hatches in 12 to 13 days. Although the female alone incubates the eggs, both sexes feed the young. Cerulean warblers raise a single brood and depart Missouri in September for their wintering grounds.

Habitat and Distribution

In Missouri, and throughout most of their breeding range, cerulean warblers are associated with mature deciduous forests, particularly in floodplains or other wet habitats. They breed from southeastern Minnesota, eastern Nebraska and eastern Oklahoma through western North Carolina, western New Jersey and western New Hampshire. Over the past 100 years this warbler has extended its breeding range to the eastern side of the Allegheny Mountains.

In Missouri, habitat around song perches of cerulean warblers is characterized by a large number of live trees over 12 inches diameter at breast height and a high closed canopy.

Cerulean warblers are reliably found near the Current, Eleven Point and Jack's Fork rivers. They occur statewide in high quality habitat, but are very scarce in the northern half of the state. Their locations as revealed by the Missouri Breeding Bird Atlas Project are shown on the following map.

The warbler's winter habitat is concentrated on the eastern slopes of the Andes Mountains in western South America. Winter habitat is mature deciduous forest with large trees, usually at elevations of 10,000 to 13,000 feet.

Cause of Historic Decline

Once one of the most abundant breeding birds in the lower Mississippi valley, the cerulean warbler population is a fraction of its original size. This decline primarily followed logging in the early part of this century. Recent surveys indicate there is a continued downward trend. In Missouri, the cerulean warbler population has declined at an average annual rate of over 5% according to 1967-1989 Breeding Bird Survey (BBS) data.

The BBS data shows range-wide a 3.4% average annual decline during the same period, despite some evidence of range expansion to the east and north. Range expansion may be due to land use changes. Areas that were logged heavily in the past are now being reforested and are attractive to cerulean warblers.

Cerulean warblers are most abundant in the central and southern states of Pennsylvania, Maryland, Virginia, and West Virginia, where populations are stable.

In Missouri, and throughout much of North America, loss of bottomland forest acreage has reduced cerulean warbler populations. On the South American wintering ground, removal of forest for coffee plantations has apparently resulted in less habitat, especially in the coffee-growing region of the northern Andes.

Current Threats to Cerulean Warbler

Loss of breeding and wintering habitat Few of the original bottomland forests still exist in Missouri. Many large mature deciduous forests have been destroyed or the forests reduced to smaller sizes in lowland areas. This has caused a loss of breeding habitat for cerulean warblers in Missouri. Smaller forests and an increase in forest edge have apparently reduced nesting success. Winter habitat is threatened by the change in coffee growing methods in the 3,000 to 9,000 feet altitude range. In the past, coffee could be grown only in the shade of large trees. This encouraged the protection of the large deciduous forests. Today sun-tolerant varieties of coffee can be grown. The forests are more likely to be cleared for growing crops; thereby reducing wintering habitat.
Other threats Cerulean warblers migrate between two continents during their yearly life cycle. They are at a higher risk than species that stay in the same area all year. Cerulean warblers produce only one brood per year. This may limit their ability to replace themselves in the population as conditions deteriorate. The effects of contaminants have not been investigated. Other possible limiting factors include diseases, parasites, weather, and human disturbance

Protection and Management: Steps Toward Recovery

Habitat preservation Large tracts, preferably of at least 1,000 acres of mature, deciduous forests, primarily in lowland areas, should be maintained. Younger hardwood stands adjacent to mature stands should be protected from timber harvest. These younger trees will provide future habitat for the warblers. Wetland-protection regulations to preserve lowland hardwood forests should be enforced. Protection of breeding habitat alone will not ensure the survival of this species. Wintering habitat can be protected with conservation easements or by purchasing the land. An educational program has started to develop a conservation stamp for consumers buying shade-grown coffee. The stamp will encourage coffee growers to preserve the large mature trees in the Andes. The protection of the trees will help save the wintering habitat for cerulean warblers and other species.
Habitat improvement Warbler breeding sites can be protected in Missouri by protecting lowland forests from timber harvest and restoring bottomland forest. Agriculture, urbanization and reservoir construction have all reduced bottomland forest acreage in Missouri. Also, chemical contamination of waterways should be reduced.
State and Federal agencies The Department of Conservation and the U.S. Fish and Wildlife Service will be conducting river surveys in Missouri to develop census techniques for cerulean warblers. These surveys will establish baseline information on warbler populations. Additionally, the Cerulean Warbler Atlas Project intends to study the species' reproductive success, delineate the precise range and quantify breeding habitat requirements.

Written by Charlene M. Bessken

Missouri and federal law prohibits the importation, transportation, sale, purchase, taking or possession of birds on the State or Federal lists, as well as their eggs and nests.

For more information on the cerulean warbler, or to report sightings of this species, contact:

Endangered Species Coordinator or Wildlife Ecologist Missouri Department of Conservation Natural History Division P.O. Box 180 Jefferson City, MO 65102

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