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NATURAL HISTORY

SOUTHWESTERN WILLOW FLYCATCHER } Empidonax traillii extimus
FAMILY: Tyrannidae

Empidonax is Latin for “mosquito king;” trailli honors medical doctor and naturalist Dr. Thomas Stewart Traill. The subspecific epithet extimus means “farthest away,” perhaps a reference to the area in which the subspecies occurs.

DESCRIPTION: The southwestern willow flycatcher is a relatively small, broad-billed bird measuring about 5.75 inches long, including the tail. It has conspicuous, light-colored wing bars and lacks the distinct eye-ring found in other flycatcher species. Upperparts are brownish olive to gray green in color; the throat is whitish, the breast pale olive, and the abdomen yellowish. While perched, the bird flicks its tail slightly upward.

HABITAT: This flycatcher can be found in thickets, scrubby and brushy areas, open second growth, swamps, and open woodland. It prefers forested areas around rivers and streams. The species is associated with cottonwood, willow, box-elder, tamarisk, Russian olive, water birch, and alder.

RANGE: The southwestern willow flycatcher breeds in Southern California, southern Nevada and Utah, Arizona, southwestern New Mexico, and western Texas. It also probably breeds in extreme northern Mexico. The bird winters in central Mexico, El Salvador, Nicaragua, Costa Rica, and rarely in Columbia. It has withdrawn from the edge of its historic range, which has become fragmented and much reduced.

MIGRATION: Southwestern willow flycatchers fly south to Central and northern South America for the winter months, migrating from late July to mid-September. Adults may leave earlier than young because they delay molting until arrival on their wintering grounds, whereas young molt prior to migration. In the spring, the birds return to the American Southwest to breed.

BREEDING: Southwestern willow flycatchers build nests made of shredded bark, cattail tufts, and grasses, usually in the fork of a willow growing near water. The eggs, which are buff-colored and dark on one end, are laid from early June through early July. The average breeding pair will produce about four eggs in four days. Two or more clutches are often laid in response to brown-headed cowbird egg parasitism, which heavily affects breeding success.

LIFE CYCLE: Egg incubation lasts 12 to 13 days; nestlings fledge after 12 to 14 days. Willow flycatchers have a lifespan of three to four years.

FEEDING: Willow flycatchers are entirely insectivorous, either hawking prey in the air or gleaning it from tree limbs. Prey species are usually flies, gnats, mosquitoes, and other terrestrial or aquatic insects.

THREATS: The southwestern willow flycatcher is imperiled by fires, water projects, livestock grazing, global warming, brown cowbird parasitism, and replacement of native habitats by introduced plant species.

POPULATION TREND: Prior to its listing as an endangered species in 1995, the southwestern willow flycatcher was declining dramatically throughout its range. Between 1993 and 2005, the number of known territories increased from 140 to 1,214, but much of the increase was due to expanded survey effort. The actual recent population trend is not known.

Photo by Suzanne Langridge, USGS