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Southwestern Willow Flycatcher

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Title: Southwestern Willow Flycatcher  
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Subject: Sacramento River, Natural Resources Conservation Service, Santa Margarita River, Colorado River Delta, San Pedro River Preserve, Fossil Creek, Sevilleta National Wildlife Refuge, Wildlife of San Juan Creek
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Southwestern Willow Flycatcher

Willow Flycatcher
E. t. extimus
)
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Tyrannidae
Genus: Empidonax
Species: E. traillii
Binomial name
Empidonax traillii
(Audubon, 1828)


The Willow Flycatcher (Empidonax traillii) is a small insect-eating, neotropical migrant bird of the tyrant flycatcher family. There are four subspecies of the Willow Flycatcher currently recognized, all of which breed in North America (including three subspecies which breed in California).[2] Empidonax flycatchers are almost impossible to tell apart in the field so biologists use their songs to distinguish between them.[3]

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-grey. The upper part of the bill is grey; the lower part is orangish. At one time, this bird and the Alder Flycatcher were considered to be a single species, Traill's Flycatcher. The Willow and Alder Flycatchers were considered the same species until the 1970's. Only their song tells them apart.[4]

Their breeding habitat is deciduous thickets, especially willows and often near water, across the United States and southern Canada. They make a cup nest in a vertical fork in a shrub or tree.

These neotropical birds migrate to Mexico and Central America, and in small numbers as far south as Ecuador in South America, often selecting winter habitat near water. Willow Flycatchers travel approximately 1,500–8,000 km each way between wintering and breeding areas.[5]

They wait on a perch near the top of a shrub and fly out to catch insects in flight, also sometimes picking insects from foliage while hovering. They may eat some berries.

This bird's song is a sneezed fitz-bew. The call is a dry whit.

This bird competes for habitat with the Alder Flycatcher (Empidonax alnorum) where their ranges overlap.

Subspecies of the Willow Flycatcher

The binomial commemorates the Scottish zoologist Thomas Stewart Traill. The four subspecies of the Willow Flycatcher are the Little Willow Flycatcher (Empidonax traillii brewsteri) (Oberholser, 1918), the Southwestern Willow Flycatcher (E. t. extimus) (A. R. Phillips, 1948), E.t. adastus (Oberholser, 1932) and E. t. traillii (Audubon, 1828).[5] The subspecies are best distinguished from each other by their songs.[6] In addition, the four subspecies have significant genetic differences based on mitochondrial DNA analysis.[7]

Southwestern Willow Flycatcher

The Southwestern Willow Flycatcher (Empidonax traillii extimus) is a federally endangered subspecies (since 1995) at which time it was known to breed at only about 75 sites in riparian areas throughout the American southwest. The known breeding population was estimated at between 300 and 500 pairs.[5] Breeding occurs from near sea level on the Santa Margarita River to 2,640 feet (800 m) at the South Fork Kern River and 3,000 feet (910 m) at upper San Luis Rey River in California and to over 8,530 feet (2,600 m) in Arizona and southwestern Colorado. The largest remaining population in California is on the South Fork Kern River, Kern County. In southern California, this subspecies breeds on the San Luis Rey River, on Camp Pendleton, Santa Margarita River and Pilgrim, De Luz, French, and Las Flores creeks; and on the Santa Ynez River. In 1996, breeding was confirmed along the Arizona side of the lower Colorado River at Lake Mead Delta and at Topock Marsh. Examination of museum specimens of 578 migrating and wintering E.t. extimus indicating that Guatemala to Costa Rica constitutes the main winter range is declining due to habitat loss and is considered to be endangered.[8] The San Pedro River Preserve was purchased by the Nature Conservancy to preserve habitat for this subspecies. North American beaver (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.[9]

Little Willow Flycatcher

The Little Willow Flycatcher, or Pacific slope subspecies of the willow flycatcher, (E.t. brewsteri) breeds in California from Tulare County (S. Laymon, pers. comm.) north, along the western side of the Sierra Nevada and Cascades, extending to the coast in northern California.[8]

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.[8]

E. t. traillii

The eastern subspecies of the willow flycatcher (E. t. traillii) breeds from the eastern coast of the United States to to the western Rocky Mountains.[5]

The winter range of the four subspecies has been elucidated using mitochondrial DNA genetic studies of 172 birds samples in winter combined with plumage coloration and morphological differences.[2]

References


External links

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