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The willow flycatcher (''Empidonax traillii'') is a small insect-eating,
neotropical The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone. Definition In biogeogra ...
migrant
bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
of the tyrant flycatcher family native to
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
.


Taxonomy

There are four subspecies recognized, all of which breed in North America (including three subspecies that breed in California). At one time, this bird and the alder flycatcher (''Empidonax alnorum'') were considered to be a single species, Traill's flycatcher. Their song is the only reliable method to tell them apart in the field. The
binomial Binomial may refer to: In mathematics *Binomial (polynomial), a polynomial with two terms *Binomial coefficient, numbers appearing in the expansions of powers of binomials *Binomial QMF, a perfect-reconstruction orthogonal wavelet decomposition * ...
commemorates the Scottish zoologist
Thomas Stewart Traill Thomas Stewart Traill (29 October 1781 – 30 July 1862) was a British physician, chemist, meteorologist, zoologist and scholar of medical jurisprudence. He was the grandfather of the physicist, meteorologist and geologist Robert Traill Omon ...
.


Subspecies

The subspecies are best distinguished from each other by their songs. In addition, the four subspecies have significant genetic differences based on mitochondrial DNA analysis. Their winter ranges have been elucidated using mitochondrial DNA genetic studies of 172 birds sampled in winter combined with plumage coloration and morphological differences. The four subspecies of the willow flycatcher are:


''E. t. brewsteri'' – Little willow flycatcher

The little willow flycatcher (''E.t. brewsteri'') is the Pacific Slope subspecies of the willow flycatcher. Described by Oberholser in 1918, it breeds in California from Tulare County north along the western side of the Sierra Nevada, and in Oregon and Washington west of the Cascade range.


''E. t. adastus''

The Great Basin/Northern Rockies subspecies of the willow flycatcher (''E. t. adastus'') breeds in California east of the Sierra/Cascade axis, from the Oregon border into Modoc County and possibly into northern Inyo County. Populations at high elevation just east of the Sierra Nevada crest but south of Modoc County are assumed to be ''E. t. brewsteri''. There has been very little study of ''E. t. adastus'' in California. It was described by Oberholser in 1932.


''E. t. extimus'' – Southwestern willow flycatcher

The southwestern willow flycatcher (''E. t. extimus'') is a federally
endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...
subspecies found in Arizona, California, Colorado, Nevada, New Mexico, Texas, and Utah. It was listed in 1995, when it was known to breed at only about 75 sites in riparian areas throughout the American southwest. The breeding population was estimated at between 300 and 500 pairs. Breeding occurs from near sea level on the Santa Margarita River to at the
South Fork Kern River The South Fork Kern River is a tributary of the Kern River in the Sierra Nevada (U.S.), Sierra Nevada of the U.S. state of California. It is one of the southernmost rivers on the western slope of the mountains, and drains a high, relatively dry p ...
and at upper San Luis Rey River in California and to over in Arizona, southwestern Colorado, and north-central New Mexico. This subspecies was described by A.R. Phillips in 1948. The largest remaining population in California is on the
South Fork Kern River The South Fork Kern River is a tributary of the Kern River in the Sierra Nevada (U.S.), Sierra Nevada of the U.S. state of California. It is one of the southernmost rivers on the western slope of the mountains, and drains a high, relatively dry p ...
,
Kern County Kern County is a county (United States), county located in the U.S. state of California. As of the 2020 United States census, 2020 census, the population was 909,235. Its county seat is Bakersfield, California, Bakersfield. Kern County compris ...
. In southern California, this subspecies breeds on the San Luis Rey River, at
Camp Pendleton Marine Corps Base Camp Pendleton is the major West Coast base of the United States Marine Corps and is one of the largest Marine Corps bases in the United States. It is on the Southern California coast in San Diego County and is bordered by ...
, the Santa Margarita River and Pilgrim, De Luz, French, and Las Flores creeks; as well as on the Santa Ynez River. In 1996, breeding was confirmed along the Arizona side of the lower
Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...
at Lake Mead Delta and at Topock Marsh. Examination of museum specimens of 578 migrating and wintering ''E. t. extimus'' indicate that
Guatemala Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...
to
Costa Rica Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...
constitutes the main winter range. This species is experiencing population declines throughout the Southwest due to habitat loss/alteration and invasive grass species. One of these is saltcedar ('' Tamarix ramosissima),'' found throughout the Southwest, where it has replaced essential vegetation by outcompeting native species in riparian areas where the southwestern willow flycatcher is found. In two sites, one in Arizona and the other in New Mexico, native trees were able to replace patches of saltcedar and populations of willow flycatchers increased. In these sites 90% of the willow flycatcher's nests were found in native vegetation, only 10% were in mixed vegetation (native species and saltcedar) and few were in areas dominated by saltcedar. However, because willow flycatchers can and do breed in some locations within saltcedar habitat, it occasionally serves as vital habitat in the recovery of this species. The San Pedro River Preserve was purchased by the
Nature Conservancy The Nature Conservancy (TNC) is a global environmental organization headquartered in Arlington, Virginia, United States. it works via affiliates or branches in 79 countries and territories, as well as across every state in the US. Founded in ...
to preserve habitat for this subspecies.
NatureServe NatureServe, Inc. is a non-profit organization based in Arlington County, Virginia, United States, US, that provides proprietary wildlife conservation-related data, tools, and services to private and government clients, partner organizations, and ...
considers the subspecies ''Imperiled.'' North American beavers (''Castor canadensis'') are thought to play a critical role in widening riparian width, openings in dense vegetation, and retention of surface water through the willow flycatcher breeding season.


''E. t. traillii''

The eastern nominate subspecies of the willow flycatcher (''E. t. traillii'') was described by Audubon in 1828. It breeds from the eastern coast of the United States to the western
Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...
.


Description

Adults have brown-olive upperparts, darker on the wings and tail, with whitish underparts; they have an indistinct white eye ring, white wing bars and a small bill. The breast is washed with olive-gray. The upper part of the bill is gray; the lower part is orangish.


Distribution and habitat

Their breeding habitat is
deciduous In the fields of horticulture and botany, the term deciduous () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed Leaf, leaves, usually in the autumn; to the shedding of petals, aft ...
thickets, especially
willow Willows, also called sallows and osiers, of the genus ''Salix'', comprise around 350 species (plus numerous hybrids) of typically deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions. Most species are known ...
s and often near water, across the United States and southern
Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
. They make a cup nest in a vertical fork in a shrub or tree. These neotropical birds migrate to
Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
and
Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...
, and in small numbers as far south as
Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...
in
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
, often selecting winter habitat near water. Willow flycatchers travel approximately each way between wintering and breeding areas. This bird's song is a sneezed ''fitz-bew''. The call is a dry ''whit''.


Food resources

Willow flycatchers are generalist insectivores, and the insects which comprise their diet vary substantially across different habitats. For example, flies of the order ''
Diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advance ...
'' made up the majority of adult willow flycatcher diets in Ontario, Canada, but only composed 10.6% of the diet of California flycatchers, who instead favor '' Lepidopterans,''
mayflies Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the order ...
, and snakeflies. They are "sit-and-wait" predators, remaining on a perch near the top of a shrub and flying out to catch insects on the wing, but are also reported to glean insects off of leaves and stems.


References


External links

* * * * * * * {{Taxonbar, from=Q903847 willow flycatcher Birds of North America Native birds of Western Canada Native birds of Eastern Canada Birds of the United States Meso-American wintering birds willow flycatcher Willow flycatcher