NEPA--Environmental Assessment

The alpine tundra group would benefit most of all the analysis groups from selecting Alternative 1.
Selection of Alternative 1 has the potential to provide direct benefits to two of the three species in
the alpine tundra analysis group (American pipit and white-tailed ptarmigan). The third species in
this group is less likely to have substantial benefit from selecting Alternative 1 because it is less
likely to be directly affected by sheep grazing activities.
Alternative 2
Selecting Alternative 2 would be substantially less beneficial for birds of conservation concern than
selecting Alternative 1, and somewhat less beneficial than selecting Alternative 3, especially for
alpine species. For all bird species of conservation concern, selecting Alternative 2 would generally
maintain current habitat conditions, and for some species, likely result in a gradual long term
improvement in habitat conditions.
Habitat conditions for some bird species is expected to continue to gradually improve under
Alternative 2 because there has been a continued decline in the number of domestic sheep grazed in
the Silverton Landscape. Numbers of domestic sheep grazing in the Silverton Landscape have
dropped about 67% from a high of about 16,000 animals in the 1960’s to about 5,300 currently. In
addition, numbers of sheep grazing on the San Juan National Forest have dropped about 95% from a
high of about 216,600 animals in the 1930’s to about 10,800 currently (SJNF 2009).
Alpine tundra represents about 38% of the habitat in the Silverton Landscape, and about 29% of the
alpine tundra habitat in the landscape is suitable for sheep grazing under current management.
Sheep obtain most of their forage and spend most of their time in the alpine zone. Alpine habitats are
also potentially the most sensitive habitats to livestock grazing because of their very short annual
growing seasons, harsh environmental conditions, frequently shallow soils, and often long time span
for vegetation recovery. The three bird species whose primary habitats occur in the alpine zone
therefore have the potential to be significantly affected by domestic sheep grazing impacts.
Of the three bird species in the alpine tundra analysis group, two (American pipit and white-tailed
ptarmigan) can be directly affected by domestic sheep grazing because they nest on the ground and
forage in areas used by grazing sheep. These two species can be directly affected through the loss of
cover at nest sites, nest trampling by grazing animals, and reduced quality of foraging habitat due to
grazing reducing plant material upon which their insect prey depends (Hoffman 2006, and Versaw
1998). The third species in the alpine analysis group, brown-capped rosy finch, is less likely to be
directly affected by grazing sheep because nests are located in rock cliff crevices and adults forage
mainly on or near snow fields, areas that are actively avoided by domestic sheep (Nelson 1998). For
these three alpine bird species of concern, selecting Alternative 2 would be least beneficial of the
three project alternatives but would result in maintaining current habitat capability or result in a
gradual long term improvement in habitat capability.
Of the seven species in the riparian/wetland group, (American dipper, black swift, cordilleran
flycatcher, and mallard) are unlikely to be affected by sheep grazing. These species usually nest in
places that are inaccessible to sheep such as in dense cover (mallard), adjacent to waterfalls (black
swift), on rock walls overhanging streams (American dipper), and in dirt cut banks (cordilleran
flycatcher). These species also typically forage in areas not frequented by sheep such as in standing
water (mallard) high above the surrounding mountain peaks (black swift), on the floor of rapidly
flowing streams (American dipper), or in the overhead forest canopy (cordilleran flycatcher). For
these reasons, selecting Alternative 2 would have little impact on habitat capability for these four
species in the riparian/wetland analysis group.
The remaining three species in the riparian/wetland group (lazuli bunting, MacGillivray’s warbler,
and Wilson’s warbler) are associated with dense willow and riparian shrublands. Field monitoring
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