NEPA--Environmental Assessment

(from nearby less contaminated populations) and the lowest breeding densities of any ptarmigan
population throughout the species’ range.
For this reason, protecting and maintaining fall and winter habitat for adult female ptarmigan is
likely to be a key factor in ensuring long-term population persistence in the landscape. Maintenance
and protection of fall and winter ptarmigan habitat is especially important given the high site fidelity
of wintering birds and the considerable numbers of adult females that are attracted from surrounding
breeding habitats to the few suitable wintering sites (Braun et al. 1976). Increasing motorized and
non-motorized recreation in preferred ptarmigan wintering areas along the Highway 550 corridor is
likely to be reducing ptarmigan winter habitat quality through increasing the extent of compacted
snow areas and increased disturbance to wintering birds. Ptarmigan populations in the Silverton
Landscape may be especially vulnerable to loss or degradation of fall and winter habitat given that
population densities in this area are lower than other parts of the species range and are likely not
self-sustaining (Larison et al. 2000).
Local bird watchers have reported consistent declines in numbers of white-tailed ptarmigan detected
over the past 5-10 years in known historic winter concentration areas around Silverton and along the
U.S. Highway 550 corridor. Most bird watchers attribute this perceived decline in the number of
wintering birds as likely caused by a coincidental substantial increase in snowmobile and nonmotorized
winter recreation in and around many historic ptarmigan wintering areas such as
Gladstone, Cement Creek, Little Molas Lake, Andrews Lake, and South Mineral Creek. Perceived
declines in the number of ptarmigan wintering around Andrews Lake, a non-motorized area, is
attributed to increased numbers of non-motorized winter recreationists that are often accompanied by
domestic dogs. Although many of these areas are within active sheep grazing allotments, no
evidence has been found that indicates grazing impacts are significantly affecting habitat capability
for ptarmigan in preferred wintering areas.
Other activities that continue to influence habitat capability for sensitive species in the Silverton
Landscape include development of private lands adjacent to public lands, increasing levels of jeep
and OHV traffic on most roads in the landscape, and mine reclamation activities that are gradually
improving water quality and downstream habitat capability. Influences that continue to affect
vegetation in the landscape and therefore affect habitat capability for sensitive species include
ongoing fire suppression, personal use firewood harvesting of standing dead trees for use as primary
home heating purposes, and natural events such as wild fire, forest insect and disease outbreaks,
wind throw events, and avalanches. All these activities have contributed to changes in the
composition, structure, and function of forested habitats in the landscape, and habitat for sensitive
species.
As the number of off-highway vehicles (OHV’s) continues to increase on most roads in the Silverton
Landscape, the potential for disturbance to wolverine in areas adjacent to popular OHV routes also
continues to increase each year. The continual annual increase in OHV use observed over the past 5-
10 years in the Silverton Landscape is likely to continue for the foreseeable future. Wolverines are
known to be very sensitive to human disturbance (Banci 1994). An aerial habitat inventory by the
Colorado Division of Wildlife and wolverine researcher Jeff Copeland determined that the central
San Juan Mountains near Silverton appeared to provide some of the highest quality potential
wolverine habitat in the state of Colorado (S. Wait pers. comm.). There are nearly annual reports of
wolverine sightings, all unconfirmed, from the central San Juan Mountains, mostly between
Silverton, Ouray and Lake City (S. Wait pers. comm.). As motorized traffic and non-motorized
recreation in formerly remote alpine areas increases, habitat capability for wolverine would be
expected to continue to decline.
85