| Southwestern
Willow Flycatcher |
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Southwestern
Willow Flycatcher (Empidonax traillii extimus
)
Terry B. Johnson, Nongame Branch Chief |
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 Scientific
Name:
Empidonax traillii extimus. Empidonax is Latin for the "mosquito king," an
apt name for these flycatchers. The specific epithet honors Dr. Thomas
Stewart Traill (1781-1862), a naturalist and medical doctor from Scotland
who helped John James Audubon find funding for his life's work, The Birds
of America. The subspecific epithet extimus means "farthest away," perhaps
a reference to the area in which the subspecies occurs.
Description:
Small; usually a little less than 6 inches in length, including tail. Conspicuous
light-colored wingbars. Lacks the conspicuous pale eye-ring of many similar
Empidonax species. Overall, body brownish-olive to gray-green above. Throat
whitish, breast pale olive, and belly yellowish. Bill relatively large;
lower mandible completely pale. Best identified by vocalizations. Call
a liquid, sharply whistled whit! or a dry sprrit; song a sneezy witch-pew
or fitz-bew. While perched, characteristically flicks tail slightly upward. |
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Habitat:
In Arizona, this flycatcher breeds principally in (at low elevations) dense
willow, cottonwood, and tamarisk thickets and woodland along streams
and rivers, and (at high elevations) pure, streamside stands of Geyer
willow. Migrants may occur more widely. |
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Distribution:
The wintering range of E. t. extimus is uncertain, but the species is known
to winter from west coast of central Mexico to northern South America.
The breeding range of extimus includes Arizona and adjacent states.
In Arizona, extimus breeds very locally along the Colorado River, the
Alamo Lake area, at the headwaters of the Little Colorado and San Francisco
rivers, along the middle Verde River, at Roosevelt Lake, and along
the middle Gila and the San Pedro rivers. Many of the breeding sites
are occupied by five or fewer pairs. |
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Biology:
Spring arrival in Arizona is in late April; fall migration begins as the
breeding season ends in July-August. Males sing repeatedly from exposed
perches while on the breeding grounds, and occasionally during migration.
The nest is built of shredded bark, cattail tufts, and grasses, and
lined with fine grasses and feathers. Usually it is placed in a branch
fork in a willow, near water. The eggs are buff with dark spots at
one end. The typical clutch of three (sometimes four) eggs is laid
in May-June. Incubation lasts 12 to 13 days; nestlings fledge after
12 to 14 days. Breeding success may be heavily affected by predation
and brown-headed cowbird egg-parasitism. |
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Status:
Extensive population reductions since the 1800s have been inferred from
comparison of historical to current occurrences. They appear to have
been caused by habitat loss (conversion or destruction of native riparian
habitats), with nest predation and brown-headed cowbird parasitism
as additional threats. Recent surveys in Arizona have documented more
than 110 pairs, on approximately 160 occupied territories. The largest
known populations in Arizona occur at Roosevelt Lake and along the
lower San Pedro River. The southwestern willow flycatcher is included
on the Department's draft list of Wildlife of Special Concern in Arizona
(AGFD in prep.). It is also considered endangered in California and
New Mexico. Much smaller populations exist in Nevada, Utah, Colorado,
and Texas. The southwestern willow flycatcher is federally listed as
endangered; a proposal to list critical habitat for Arizona and elsewhere
is pending. |
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Management
Needs:
The most urgent needs are: a better understanding of habitat requirements;
public-private partnerships that focus on protection of existing willow-cottonwood
thickets, and restoration where such habitats have already been destroyed
along rivers and streams; continuation of ongoing statewide surveys and
monitoring coordinated by Arizona Game and Fish through Arizona Partners
in Flight, a group of agency and nongovernmental organizations working
together for nongame landbird conservation; and research into the relationship
of nest predation and cowbird parasitism to willow flycatcher breeding
success. |
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