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THE SOUTHWESTERN WILLOW FLYCATCHER AN ENDANGERED SPECIES IN THE COLORADO RIVER DELTA

THE SOUTHWESTERN WILLOW FLYCATCHER AN ENDANGERED SPECIES IN THE COLORADO RIVER DELTA. VANDA J. GERHART ENVIRONMENTAL RESEARCH LABORATORY UNIVERSITY OF ARIZONA. Southwestern Willow Flycatcher ( Empidonax traillii extimus). Neotropical migratory bird.

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THE SOUTHWESTERN WILLOW FLYCATCHER AN ENDANGERED SPECIES IN THE COLORADO RIVER DELTA

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  1. THE SOUTHWESTERN WILLOW FLYCATCHER AN ENDANGERED SPECIES IN THE COLORADO RIVER DELTA VANDA J. GERHART ENVIRONMENTAL RESEARCH LABORATORY UNIVERSITY OF ARIZONA

  2. Southwestern Willow Flycatcher (Empidonax traillii extimus) • Neotropical migratory bird. • 1995. Placed on endangered species list by USFWS • 1997.Critical habitat designation enacted. • 18 critical habitat units totaling 599 river miles in AZ, CA, & NM.

  3. Description • Small passerine bird. • 15cm long, weight ~12 g • Greenish -brownish gray above • White throat • Pale olive breast • Pale yellow belly • 2 white wing bars present • Eye-ring faint to absent • Upper mandible dark, lower light. Distinguishing feature is its song. The Fitz-bew and Whitt.

  4. Geographic Range of the Willow Flycatcher • Wintering habitats: • Known: Costa Rica, Belize. • Probable: Central America, N. South America, Southern Mexico. • Migration Routes: Unknown • Breeding Grounds: • S.W. United States, • N. Sonora, • N. Baja

  5. Breeding Range and Distribution of Willow Flycatcher Subspecies. Adapted from Unitt 1987 and Browning 1993

  6. HABITAT • Dense riparian habitat from sea level to 2600 m. • < 18 m from water or saturated soil. • Plant species composition: monotypic to mixed species. • Habitat structure: Live foliage density high from the ground to the canopy. • Nesting sites located in riparian habitats wider than 10m.

  7. THREATS TO CRITICAL BREEDING GROUNDS OF THE SOUTHWESTERN WILLOW FLYCATCHER • EXTENSIVE LOSS, FRAGMENTATION & MODIFICATION OF RIPARIAN AREAS • Causes: • Urban encroachment • Recreation & Agriculture • Fire • Water diversion • Water impoundment • Channelization • Livestock & grazing • Exotic vegetation

  8. NESTING HABITS • Nest height variable: range 2 to 7 m above ground. • Nests: 8 cm h x 8 cm w. • Nests typically in fork of branch. • Clutch size: 3-4 eggs. • Incubation:12-13 days. • Fledge 12-15 days. • Stay close to nest 3-5 days • Remain in natal area 14-15 days. Brood parasitism by brown-headed cowbird (Molothrus ater).

  9. CURRENT POPULATION ESTIMATES • 300 to 500 pairs • 75% of locations there are 5 or less territorial birds. • 20% of locations there are single, unmated birds.

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