Photo courtesy of Greg Lavaty

Cerulean Warbler

Dendroica cerulea
Order: Passeriformes
Family: Parulidae
Listen:
Sound courtesy of Cornell Lab of Ornithology

Did you know?

The Cerulean Warbler could be considered the signature bird of the Shade Coffee movement. Due to habitat loss in both its breeding and winter ranges, this warbler's population is in steep decline.

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General Description

The male Cerulean Warbler is blue above, white below, and has a narrow blue-black "necklace" around its throat. Its color is often described as azure or sky-blue. The adult female is bluish-green above, with a yellowish tinge below. Both sexes have white wing bars and white tail spots in all plumages. This warbler's nest is placed on a horizontal branch so it is hidden by leaves from above and has open space below. When leaving the nest, the female initially falls like a leaf with her wings folded until she is near the ground; then she opens her wings and flies horizontally.

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Habitat & Migration

During breeding season, this warbler builds its nest and forages high in the canopyThe uppermost layer in forest habitat.
More... of older and mature deciduousA tree or shrub that sheds its leaves at the end of each growing season.
More... forests. It prefers large tracts of forest consisting of a variety of hardwood tree species and relatively little undergrowth. It breeds in selected areas of the eastern and central United States and southern Canada, at altitudes up to 3,500 feet. Cerulean Warblers are difficult to see on their breeding grounds because they spend much of their time high in the canopy foraging silently on leaves for caterpillars and other insects.

The Cerulean Warbler winters on the eastern slopes of the Northern Andes in Colombia, Venezuela, Ecuador, and northern Peru. It migrates further than many other warblers, and tends to start its migration early. In a study in Colombia, all the Cerulean Warblers had left their wintering sites by early in April; juveniles started returning to the wintering grounds near the end of August, followed by adults arriving in early September.

As part of conservation efforts to preserve needed habitat, the bird's migration route is being intensely studied. Recent findings show that the birds begin their spring migration to the breeding grounds by flying approximately 1,000 miles over the Caribbean Sea to reach Nicaragua and Belize. They forage there for several weeks in the coastal forests and further inland, possibly to replenish fat reserves. The migration back to the breeding grounds is completed by flying across the Gulf of Mexico to Mississippi, Alabama, Louisiana, and Georgia, and continuing north and northeast. The fall migration route is still unclear, with some studies suggesting the birds use a more eastern route for the journey south. Ongoing research will identify additional stopover points and will try to determine whether some of the birds fly nonstop from the Gulf states to their wintering grounds.

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The Coffee Connection

The Cerulean Warbler winters in humid broadleaved evergreen forests on the eastern AndeanThe South American mountain chain that runs parallel to the continent's west coast.
More... slopes, generally at altitudes between 2,500 and 5,000 feet. These conditions are also favorable for growing coffee, coca, and other crops, which has led to rapid degradation of these Andean forests. In these areas, this warbler is found in smaller forest patches and in more open canopies than in North America.

In Venezuelan shade coffee farms, it forages primarily in the shorter trees and shrubs, although not directly on coffee plants. It mainly eats caterpillars, spiders, and large flies. In the same study, the authors observed adult male Cerulean Warblers foraging on epiphytesPlants that grow harmlessly on other plants - usually trees - rather than in the ground.
More... such as orchids and bromeliads. Farmers often remove epiphytes because they believe that the epiphytes may harm the trees and that a more open canopy improves coffee yield. However, epiphytes provide birds with several important resources, including nesting sites and material, water, and food such as fruit, nectar, insects, and other small prey. Trees whose epiphytes have been removed attract smaller numbers of birds than undisturbed trees.

In Colombian shade coffee plantations, Cerulean Warblers and other migrants also forage on or near canopy flowers such as those from ErythrinaA genus of flowering tropical trees used to provide shade in coffee plantations. Some shade coffee birds use Erythrina flowers and nectar.
More... trees. Researchers do not know how the Cerulean Warbler uses these canopy flowers; the bird could feed on nectar or pollen, or on insects attracted to the flowers.

On their wintering grounds, Cerulean Warblers occur in mixed flocks consisting of a variety of species. The makeup of the flocks varies locally. In one study in Colombia, 73 resident and migratory bird species were identified in flocks containing Cerulean Warblers.

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Conservation Status

According to data from the North American Breeding Bird Survey, this warbler's current population has declined over 80% since the mid 1960s. This sharp decline is caused primarily by loss of the forest habitats it needs for breeding in North America and for wintering in South America.

Many efforts are being made to conserve breeding, non-breeding, and migratory habitats for the Cerulean Warbler. It is on the Audubon Watch ListA list of birds in the U.S. that are in need of immediate conservation help.
More..., and is also recognized as a species of conservation concern through Audubon's Important Bird Areas programA global effort by the National Audubon Society to identify and conserve vital areas for biodiversity, with a focus on critical habitat for birds.
More.... Attempts to categorize the bird as 'threatened' under the United States Endangered Species Act had not succeeded as of November 2008. It is, however, listed as a species of special concern in Canada, where it is protected. Additionally, the Cerulean Warbler is considered "Vulnerable" by the International Union for Conservation of NatureA global environment network which publishes a "Red List" indicating the conservation status of plants and animals. Status on the “Red List” increases from Least Concern to Near Threatened to Vulnerable to Endangered to Critically Endangered.
More... (IUCN).

A team of international scientists formed the Cerulean Warbler Technical Group to share their on-going research. Scientists are trying to learn when in their life cycle Cerulean Warblers are especially vulnerable. A study of a breeding population in southern Ontario, Canada, suggests that events during migration or on the non-breeding grounds caused most of the mortality in banded adult males.

Since 2002, ProAves Colombia (a foundation formed to protect birds of conservation concern and their habitat) has established eleven bird reserves in the prime coffee growing areas of Colombia, of which seven are important for the Cerulean Warbler. One reserve focuses specifically on the Cerulean Warbler; this is the only Colombian reserve dedicated to a migratory songbird. ProAves strives to educate farmers, communities, and especially school-aged children about migratory song-birds and the shade coffee connection, and it is currently developing a Cerulean Warbler Conservation Plan to increase the amount of protected habitat available to this warbler. Since 2004, ProAves has sponsored and coordinated an annual Migratory Bird Festival in Colombia (recently expanded to Ecuador, Peru, and Bolivia).

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