Black-throated Gray Warbler (Dendroica nigrescens)

Distribution

Breeding: Extends from southwestern British Columbia, western Washington, and central Oregon across southern Idaho to western Wyoming, south (primarily in the mountains) to Arizona, southern New Mexico, northern Baja California, and northeastern Sonora, Mexico.

Winter: Primarily Mexico, found in Baja California Sur and the Pacific Slope and interior of Sonora, Durango, Zacatecas, and Coahuila south to central Oaxaca. Winters in small numbers in California and southern Arizona; casually along Gulf Coast of U.S.

Breeding habitat

Breeds in a variety of semi-arid woodlands, dry, open forests, and chaparral. In the Pacific Northwest, birds occur in deciduous and coniferous secondary growth in old clear cuts and burns, as well as in mature or old growth forests. Breeds at higher elevations in the rest of the range, preferring dry, open woodlands (e.g. pinyon-juniper, valley-foothill hardwood-conifer, and montane hardwood habitats); often associated with oaks throughout its range.

Conservation status

This warbler is of moderate conservation importance, because of its relatively small and patchy breeding and wintering distributions. Populations appear to be stable at present, and this species may be relatively tolerant of silvicultural practices and other disturbance. Little is known, however, about its specific habitat requirements or sensitivity to largescale land-use practices in the western United States.

Description

Male: Gray above and white below, with a bold face pattern. Purely black chin, throat, cheek patch, and crown, set off by a white supercilliary and crescent-shaped cheek patch; also black streaks on sides of breast and flanks. A yellow loral spot (between the eye and the beak) stands out, as do the two white wing bars easily seen on the gray wings.

Female: Similar to adult male, but the black areas on the head are more grayish. Instead of a black throat, a band of gray extends from the neck across the lower throat, although some females can show black extending on the throat resembling males. Also shows two white wing-bars and yellow loral spot.

Juvenile: Upperparts are dull-brown with a dark crown and broad, dull, whitish eyebrow. Underparts are dull gray, becoming whiter on the belly; a hint of the white wing bars and white in the tail may be visible.

Vocalizations

Songs: Two types of primary song are known. The female is not known to sing.

Type 1 song: More common in early breeding season when male is close to female, decreases in frequency after mating. It consists of 5–9 buzzy notes, full of “zee”s, having a crescendo effect with an emphatic ending: zee-zee-zee-zee-bzz-ZEE, zee-zee-zee-eeCHEW.

Type 2 song: Given in interactions with other males and become more common later in breeding season. Buzzy like the Type 1 song, they are given at a faster rate and are more variable, often lacking the inflected ending.

Calls: A sharp, nontonal thick or tup. A high sip, or see, is given in flight.

Foraging strategy

Forages at mid-levels in the canopy, primarily foliage gleaning, with occasional hover-gleaning and rarely flycatching.

Diet

Insectivorous, only “small, green caterpillars” specifically mentioned as a common prey item. Also known to eat ants.

Behavior and displays

• Territories are established by male, which sings from prominent perches to advertise boundaries to conspecific males; intruders are chased out of territory when found.

Courtship

• No information.

Nesting

Nest Site: Little information, but generally in trees or shrubs 3–32 feet (1–10 meters) above ground. In trees, nests placed well out on limbs. Nests have been found in pinyon pine, (northern New Mexico), on a horizontal branches 3.5–10 feet (1.2–3.0 meters) from the trunk of oaks or junipers (southeastern Arizona), on horizontal branches of fir or in crotches of an oak (Washington and Oregon).

Height: Generally low, but can range from3–35 feet (0.9–10.7 meters) above ground.

Nest: Male never observed assisting building nest, but may follow female and scold almost continuously. The deep, compact cup nest constructed of grasses, bark, and dead forb stalks, often lined with feathers and hair of cattle.

Eggs: 3–5, usually 4, white, creamy-white, or greenish-white eggs are speckled, dotted, or blotched with reddish brown and umber.

Incubation period: Little information, incubation is done by female alone.

Nestling period: Appearance not described, but young are altricial and nidicolous (helpless, nearly naked confined to nest). Young are tended by both parents.

Fledgling period: Young leave nest, apparently in response to alarm calls of female, when nest closely approached for photography. No other information.

Broods: Double brooded in at least some parts of the breeding range.

Cowbird Parasitism: Rare host of the Brown-headed Cowbird, only 20–30 records.