The southwestern willow flycatcher, known by its scientific name, Empidonax traillii extimus is a small member of the tyrant flycatcher family. An insect-eating, neotropical migrant bird, the southwestern willow flycatcher is a federally endangered subspecies.
The breeding range of the southwestern willow flycatcher includes Southern California, Arizona, New Mexico, extreme southern portions of Nevada and Utah, far western Texas, perhaps southwestern Colorado, and extreme northwestern Mexico. In Nevada this subspecies can be found along the Virgin River, lower Muddy River, Colorado River, and Pahranagat Valley.
It was listed as endangered in 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. Breeding occurs from near sea level on the Santa Margarita River to 2,640 feet above sea level at the South Fork Kern River and 3,000 feet at upper San Luis Rey River in California and to over 8,530 feet 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, at Camp Pendleton, the Santa Margarita River and Pilgrim, De Luz, French, and Las Flores creeks; as well as on the Santa Ynez River and in the environs of Mill Creek near Highland and Mentone. 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. This species is experiencing population declines throughout the Southwest due to habitat loss/alteration and invasive species.
The southwestern willow flycatcher breeds in relatively dense riparian tree and shrub communities associated with rivers, swamps, and other wetlands including lakes and reservoirs. In most instances, the dense vegetation occurs within the first 10 to 13 feet above ground. Habitat patches must be at least one quarter acre in size and at least 30 feet wide. Historically the southwestern willow flycatcher nested in native vegetation including willows, seepwillow, boxelder, buttonbush, and cottonwood. Following modern changes to riparian communities, this subspecies still nests in native vegetation, but also uses thickets dominated by non-native tamarisk and Russian olive, or in mixed native non-native stands. The flycatcher builds a small open cup nest, most often 6.5 to 23feet above ground in a fork or on a horizontal branch of a medium-sized bush or small tree with dense vegetation above and around the nest.
A typical clutch size is three to five eggs that are creamy white or buff dotted with dark irregular markings around large end. Upon hatching, nestlings are helpless and with only small patches of down.
Adults of this species have brown-olive upperparts, darker grayish-green on the wings and tail, with a whitish or pale yellowish belly. 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.
These birds have a length of 5.2 to six inches, a weight of around .48 ounce, a wingspan of 8.5 inches and a tail of about 2.5 inches.
A southwestern willow flycatcher catches insects while flying, hovers to glean them from foliage, and occasionally captures insects on the ground.