Cerulean Warbler (Dendroica cerulea)

Distribution

Breeding: From southeastern Nebraska across the southern Great Lakes region to southern Ontario, southwestern Quebec, and western New England, south to northern Texas, Arkansas, northern Alabama, and northern Georgia. Most abundant in the Cumberland Plateau and surrounding regions; rare east of the Appalachian Mountains.

Winter: Primarily on the eastern slopes of the Andes from Colombia and Venezuela through Ecuador to Peru. Relatively few overwinter elsewhere, though a small population exists in the tepui region of Venezuela.

Breeding habitat

Most commonly found in large, contiguous forest tracts, composed of structurally mature hardwoods with a high, variably closed canopy. Tree size is of primary importance, both height and diameter at breast height (DBH). Birds are found almost always above the midpoint of a tall tree, often in the canopy; and are usually found in stands where most trees fall into the larger DBH classes. Specific forest types vary throughout the species’ range and include bottomland hardwood and riparian forests (especially with tall sycamores or cottonwoods), dry ridgetops with mature oaks and hickorys, mesic cove forests with tulip-poplar and other southern hardwoods, red-maple swamps, and lake margins.

Conservation status

Description

Male: Among the smallest of our warblers, shows a short tail, and a plump body. Cerulean blue upperparts, brightest on the head. Back variably streaked with black, two white wing bars are prominent. White underparts with a dark blue or black line across the throat, flanks are streaked with blue-gray or black. A lighter blue eyebrow sometimes evident.

Female: Somewhat similar to male, except greenish above, washed with blue, especially on the rump, no black streaking on back. The underparts are washed with yellow, the flanks and sides of breast have indistinct dusky streaking. The head shows a bluish-green crown and cheek, setting off a whitish or yellowish eyebrow.

Juvenile: Brownish-gray above, underparts dull and buffy. Wings are dusky-gray with two whitish wing bars, may show some gray-green on flight feathers and coverts. Crown brownish-gray, eyebrow buffy-white, eye line is brownish.

Vocalizations

Songs: A fast, buzzy song, rising in three stages, zeep zeep zeep zeep zizizizi zee! or zray zray zray zray-zray zreee! Can be confused with the song of the Northern Parula, although the terminal, high-pitched buzz of the Cerulean’s song is diagnostic. The song of the Black-throated Blue Warbler also is similar, though slower with fewer notes.

Calls: A full, slurred, chip; flight note a short, buzzy dzzt, or zzee.

Foraging strategy

Systematically hops along the upper branches from the main trunk outward to the smaller, peripheral branches, gleaning the underside of leaves and twigs. Birds almost always occur above the midpoint in large trees, usually in the canopy. Sometimes sallies or hovers for aerial insects.

Diet

Poorly known, but includes adult and immature insects. One examination of stomach contents indicated that wasps, beetles, weevils, and caterpillars were consumed in varying proportions. Other studies report ants, sawflies, and locusts are also taken.

Behavior and displays

• Generally hops on small branches and twigs in the forest canopy in lateral or slightly upward direction.

• Usually short, direct flights between trees, occasionally accompanied by fluttering or slow flapping and spread tail that makes the white patches in the tail and on the inner vanes of the primaries and secondaries obvious.

• Breedering birds can be very aggressive: males sometimes attack each other at canopy heights greater than 60 feet (20 meters), meeting in mid-air with audible collision. The birds grapple with each other with bills and feet as they fall, spiraling to the ground with spread wings and tails; similar fights observed between females.

Courtship

• Poorly studied: courtship displays, mate-guarding, and pre- and post-copulatory displays have not been described.

Nesting

Nest Site: The nest is typically placed at a considerable distance (6–25 feet, 2–7 meters) from the bole of a large tree, usually saddled on a large, lateral branch, sometimes attached to a small protruding twig. Variation in site selection is considerable, particularly with respect to the distance from the bole. Builds in a variety of trees, most often oaks, elms, and American sycamore. More information is needed on nest site preferences, especially the relationship (if any) to canopy gaps.

Height: Varies greatly, but most are located from 10–40 feet (3–12 meters), can range to over 65 feet (20 meters).

Nest: The shallow cup is built by the female, constructed of finely woven grass, plant stems/fibers, tree bark, mosses, and lichens, the entire structure is bound together on the outside with spider silk. The cup is lined with plant fibers and moss.

Eggs: 3–5 ( usually 4) creamy-white, grayish-white or very pale greenish white eggs are speckled, spotted, and blotched with chestnut-red, reddish-brown, or purplish-brown and paler brownish-gray.

Incubation period: 12 days, only the female incubates. The male occasionally feeds the female while she incubates.

Nestling period: Poorly documented, but both parents feed insects to the young. Initially the male provides the most food, later the female increases her feedings as she devotes less time to brooding young. Young leave the nest at 9–11 days.

Fledgling period: Young first move to lower-level vegetation where their parents feed them, and then gradually farther afield as they approach independence.

Broods: Single brooded.

Cowbird Parasitism: Little information available, but parasitism may be an important factor in the decline of the species.