8031

• UCREFRP Catalog Number: 8031
• Author: U.S. Department of the Interior.
• Title: Fish and Wildlife Service Final Biological and Conference Opinion on Lower Colorado River Operations and Maintenance - Lake Mead to Southerly International Boundary.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

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BIOLOGICAL OPINION

Status of the Species

counties from San Diego Co. north to San Luis Obispo Co., as well as in the inland counties, i.e.,
Kern, Inyo, Mohave, San Bernardino, and Imperial. Unitt (1987) documented that the flycatcher
had been extirpated, or virtually extirpated (i.e., few territories remaining) from the Santa Clara
River (Ventura Co.), Los Angeles River (Los Angeles Co.), Santa Ana River (Orange and
Riverside counties), San Diego River (San Diego Co.), lower Colorado River (Imperial and
Riverside counties and adjacent counties in AZ), Owen's River (Inyo Co.), and the Mohave River
(San Bernardino Co.). Its former abundance in California is evident from the 72 egg and nest sets
collected in Los Angeles County, alone, between 1890 and 1912, and from Herbert Brown's 34
nests and nine specimens taken in June of 1902 from the lower Colorado River near Yuma. Local
collections of this magnitude suggest both a keen understanding of flycatcher habitat use on the par t
of the collector and that this subspecies was locally very abundant.

Survey and monitoring efforts since the late 1980s have confirmed the southwestern willow
flycatcher's presence at 18 locations on 11 drainages in southern California (including the Colorado
River). Current known. flycatcher breeding sites are restricted to four counties, San Diego,
Riverside, Santa Barbara, and Kern. Combining survey data for all sites surveyed since the late
1980s for a composite population estimate, the total known southwestern willow flycatcher
population in southern California is 114 territories (Table 6).

Of the 18 sites where flycatchers have been documented in California, 72 % (13) contain five or
fewer territorial flycatchers; 17% (3) contain six to 10 territorial flycatchers; and 11 % (2) contain
20 or more territorial flycatchers. Of all the sites statewide, 22 % (four sites) have single pairs or
unmated territorial birds and only three drainages are known to have 20 or more flycatcher
territories in total, i.e., the San Luis Rey River (San Diego Co.), South Fork Kern River (Kern
Co.), and Santa Ynez River (Santa Barbara Co.).

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