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

I
I
I
,
I
I
I
I
I
I
I
I
I
'I
I
I
I
I
I

BIOLOGICAL OPINION

Status of the Species

The Pecos and Rio Grande rivers in western Texas are considered the easternmost boundary for
the southwestern willow flycatcher. Unitt (1987) found specimens from four locations in Brewster,
Hudspeth, and Loving counties where the subspecies is no longer believed to be present.
Landowner permission to survey riparian areas on private property has not been obtained; thus
current, systematic survey data is not available for Texas. There have been no other recent
reports, anecdotal or incidental, of willow flycatcher breeding attempts in the portion of western
Texas where E,t. extimus occurred historically. Given that surveys in adjacent Dona Ana County ,
New Mexico, have failed to document breeding along historically-occupied portions of the Rio
Grande, the Service believes the southwestern willow flycatcher has been extirpated from Texas.

Colorado

The taxonomic status and the historic distribution and abundance of willow flycatchers in
southwestern Colorado remains unclear due to a lack of specimen data and breeding records.
Preliminary data on song dialects suggests that the few birds recently documented in southwestern
Colorado may be E.t. extimus. These sightings have prompted State and Federal agencies to
delineate provisional boundaries for E,t, extimus and sponsor statewide survey efforts. Survey
efforts since 1993 have documented a total of six locations in Delta, Mesa, and San Miguel
counties where willow flycatchers have been found (Table 6). Two locations have single, unmated
males; two locations have single pairs; the remaining two locations are comprised of four to five
territories each,

Utah

Specimen data reveal that E.t. extimus historically occurred in southern Utah along the Colorado
River, San Juan River, Kanab Creek, Virgin River, and Santa Clara River (Unitt 1987). The
northern boundary of E.t, extimus in south-central Utah remains unclear due to a lack of specimen
data from that region. The southwestern willow flycatcher no longer occurs along the Colorado
River in Glen Canyon where Lake Powell inundated historically-occupied habitat, nor in unflooded
portions of Glen Canyon near Lee's Ferry where flycatchers were documented nesting in 1938.
Similarly, recent surveys on the Virgin River and its tributaries and Kanab Creek have failed to
document the presence of flycatchers (McDonald et al. 1995), Single, territorial males and
possibly a pair of flycatchers were documented at two locations on the San Juan River (San Juan
Co.) in 1995, but breeding was not confirmed (Sogge 1995b, R. Marshall, pers. obs.). The
population totals for Utah are summarized in Table 6.

Nevada

Unitt (1987) documented three locations in Clark County from which E,t. extimus had been
collected, but not found after 1970. Current survey efforts have documented a single location with
two unmated males on the Virgin River in Clark County (Tomlinson in litt.)(Table 6).

63