Difference between revisions of "Southwestern Willow Flycatcher- EP"

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''CRE AT-RISK SPECIES VIGNETTES – Larry Stevens''
 
''CRE AT-RISK SPECIES VIGNETTES – Larry Stevens''
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*'''Kanab Ambersnail'''
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*'''Southwestern Willow Flycatcher'''
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*Federally endangered since 1991, the Kanab ambersnail [KAS; Oxyloma haydeni haydeni (kanabensis; Pilsbry 1948)] is a half inch-long, dextral (up-to-the-right-spiraling) landsnail with a high, delicate spire, and which only exists in three spring-fed wetlands in southern Utah and northern Arizona.  
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*The southwestern willow flycatcher (SWWF; Empidonax trailii extimus Phillips 1948) wa listed as endangered in 1993.
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*Discovered in Grand Canyon during tributary monitoring at Vaseys Paradise in 1990, this hermaphroditic species has an annual life cycle.  
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*It is a small, greenish flycatcher with white wing bars, and has an upright roosting posture.  
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*Eggs are laid in August, larval snails grow until mid-October, then overwinter by sealing themselves with mucous to stone, wood, or (often unfortunately) dead leaves, which may blow away.  
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*Like the other three subspecies of willow flycatcher, it has a distinctive “fitz-bew” call. Originally ranging from near sea level to over 8,500 ft in elevation, SWWF occurred throughout Arizona and New Mexico, and in southern Texas, California, Nevada, and Utah.  
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*Those snails that survive the vicissitudes of winter emerge in March or April, complete their growth by mid-summer and breed.  
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*The flycatcher commonly nests from 2-5 m above the ground, often adjacent to, or over water.  
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*Those with female function lay several clutches of about 40 eggs in gelatinous masses on the undersides of moist stems and leaves. KAS feeds on biofilm on moist, dead stems of cardinal monkeyflower and other wetland plants, but they seem to prefer feeding on the tender new leaves of non-native watercress.  
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*Intensive surveys and monitoring over the past two decades have revealed 300-500 SWWF nesting pairs throughout its historic range.  
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*About 10% of adult KAS at Vaseys Paradise are infected with a parasitic Leucochloridium flatworm, which evacuates from the snail in August and completes its life cycle in songbirds. Although common in Utah, only two other natural populations of Oxyloma ambersnails occur in Arizona, one at Leopard Frog Marsh at Mile -9L and the other at Indian Gardens on the Bright Angel Trail in central Grand Canyon.
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*In Grand Canyon, a predam nesting record was reported at Lees Ferry, four pairs nested between Miles 50-71 until about the Year 2000, and nesting occurred along Havasu and Spencer Creeks and at several riparian sites near uppermost Lake Mead.  
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*After scouring springtime floods were eliminated by Glen Canyon Dam in 1963, Vaseys Paradise vegetation cover expanded by about 40% to nearly an acre.  
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*However, no nesting pairs have been documented in recent years.  
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*The post-dam KAS population there is now likely substantially greater than it was in predam time.
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*Nearly all nests in Grand Canyon have been in tamarisk, despite the availability of nearby, apparently suitable native vegetation.  
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*The endangered status of KAS has resulted in several Biological Opinions from the U.S. Fish and Wildlife Service regarding the impacts of planned high flow experiments.  
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*Typically, more than 80% of the nests found in Arizona each year occur in tamarisk, prompting the U.S. Fish and Wildlife Service to declare some tamarisk-dominated reaches as critical SWWF habitat.  
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*Actions to protect the Vaseys snail population have included: developing secondary, off-river KAS populations in tributaries; transporting all KAS in the mainstream flood zone to higher elevations; moving and protecting vegetation patches that support KAS; and monitoring flood impacts and among-year population variation.  
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*Reasons for the decline of SWWF include degradation of winter habitat in Central America and breeding habitat in the Southwest, as well as brood parasitism by brown-headed and bronzed cowbirds (Molothrus ater and M. aeneus, respectively).  
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*Detailed morphological and genetics analyses by the U.S. Geological Survey will soon propose synonomy of Kanab ambersnail into the more widespread and common North American Niobrara ambersnail taxon (Oxyloma h. haydeni Pilsbry 1948), thus Kanab ambersnails will soon no longer exist as a taxonomic entity.
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*Cowbirds pitch SWWF eggs from the nest, replacing them with their own eggs, and the SWWF may raise the cowbirds as their own young. The recent invasion of tamarisk leaf beetle in northern Arizona severely threatens remaining SWWF with further loss of habitat.

Revision as of 16:39, 19 April 2013

CRE AT-RISK SPECIES VIGNETTES – Larry Stevens

  • Southwestern Willow Flycatcher
  • The southwestern willow flycatcher (SWWF; Empidonax trailii extimus Phillips 1948) wa listed as endangered in 1993.
  • It is a small, greenish flycatcher with white wing bars, and has an upright roosting posture.
  • Like the other three subspecies of willow flycatcher, it has a distinctive “fitz-bew” call. Originally ranging from near sea level to over 8,500 ft in elevation, SWWF occurred throughout Arizona and New Mexico, and in southern Texas, California, Nevada, and Utah.
  • The flycatcher commonly nests from 2-5 m above the ground, often adjacent to, or over water.
  • Intensive surveys and monitoring over the past two decades have revealed 300-500 SWWF nesting pairs throughout its historic range.
  • In Grand Canyon, a predam nesting record was reported at Lees Ferry, four pairs nested between Miles 50-71 until about the Year 2000, and nesting occurred along Havasu and Spencer Creeks and at several riparian sites near uppermost Lake Mead.
  • However, no nesting pairs have been documented in recent years.
  • Nearly all nests in Grand Canyon have been in tamarisk, despite the availability of nearby, apparently suitable native vegetation.
  • Typically, more than 80% of the nests found in Arizona each year occur in tamarisk, prompting the U.S. Fish and Wildlife Service to declare some tamarisk-dominated reaches as critical SWWF habitat.
  • Reasons for the decline of SWWF include degradation of winter habitat in Central America and breeding habitat in the Southwest, as well as brood parasitism by brown-headed and bronzed cowbirds (Molothrus ater and M. aeneus, respectively).
  • Cowbirds pitch SWWF eggs from the nest, replacing them with their own eggs, and the SWWF may raise the cowbirds as their own young. The recent invasion of tamarisk leaf beetle in northern Arizona severely threatens remaining SWWF with further loss of habitat.
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