THE SOUTHWESTERN WILLOW FLYCATCHER

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

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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.
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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

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

• Dense riparian habitat from sea level to
  2600 m.
• lt 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.

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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

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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.
• Incubation12-13 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).
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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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