WSP08242 - Laserfiche WebLink

Home Browse Search

Southwestern Willow Flycatcher By: Debra T. Bills, U.S. Fish and Wildlife Service Bryan T. Brown, Consulting Ecologist II The Southwestern willow flycatcher (Empidonax traillii extimus) is a rare riparian bird fOWld in Arizona, Ne\'" Mexico, and southern California. The extimlJ.s subspecies of willO\\' flycatcher is rarest in Arizona. In 1987, approximately 2S pairs of willow flycatchers were believed to he in Arizona, \\;th the largest population-7 pairsnin the Grand Canyon. A 1991 slln'ey of ....illow flycatchers below Glen Canyon Dam in the Glen Canyon National Recreation Area and Grand Canyon National Park located only two nesting pairs. The most probable reason for the apparent decline in the Grand Canyon is brood parasitism by brown-headed cowbirds. Instead of making their own nests, brown-headed cowbirds lay their eggs in other species nests, usually at the expense of their host's young. If the host's young or eggs are not pushed out of the nest by the adult cowbirds, the young willow flycatchers usually succumb to competitive pressure from the larger, more aggressive young cowbirds. Compounding the threat of cowbird parasitism is habitat t Y t!~ ~- fragmentation caused by floods and fluctuating flows. Fluctuating r~ ~l ~,.. flows contribute to the erosion of terrestrial habitats, resulting in .. J ~ decreased size of contiguous vegetation patches. Many species ,. -,Jft.. require specific threshold patch sizes for nesting. Although the r. required specific patch size for nesting willow flycatchers is not known, it is known that the brown-headed cowbird prefers small patch sizes and habitats with a high edge to center ratio. The willow flycatcher is a neotropical migrant songbird which arrives in Arizona in early May. and in the Grand Canyon area around May 15. Nesting begins in late May and continues through July_ The average clutch is three or four eggs, and incubation is complete in about 12 days. The nestlings spend another 12 days or so on the nest. I" ," Although the willow flycatcher has traditionally been associated with willows and other native riparian vegetation, all of the nests locdted in the Grand Canyon have been located in tamarisk (salt cedar), even though nath'e vegetation was available. These secretive birds are almost impossible to visually distinguish from other subspecies of willow flycatchers. However, since the southwestern subspecies is the only willow flycatcher known to breed in Arizona, finding a nest or hearing the classic male "fitz bew" song during the breeding season is a good indication that it is the extimus subspecies. The Arizona Game and Fish Department considers the willow flycatcher as endangered in Arizona. The US Fish and Wildlife Service classifies the willow flycatcher as a Category 1 species. (A species or subspecies for which there is substantial information to support the biological appropriateness of proposing to list it as threatened or endangered.) If you have any questions or information on this species, please contact Debra Bills or Sam Spiller, Field Supen-isor. U.S. Fish and Wildlife Service, Phoenix, Arizona. (602) 379-4720. , Skrklt by Brio" Ero"J 12