Using Western Landscapes - Mountains and Plains: The Ecology of Wyoming Landscapes - page 310

Fig. 18.5. Most of Wyoming is acces-
sible by roads, though many are not
easily traveled or are private. With or
without fences, they affect the move-
ments of pronghorn, deer, elk, and
sage-grouse. Moreover, their impacts
extend beyond the roadbed, contribut-
ing further to habitat fragmentation.
Photo by Ken Driese.

food. Some native animals have become locally extinct,
or their populations have declined. examples in forested
landscapes include the lynx, wolverine, grizzly bear, great
gray owl, boreal owl, northern goshawk, and northern fly-
ing squirrel. in grasslands and shrublands, declining spe-
cies include the sage-grouse, sage sparrow, sage thrasher,
Brewer's sparrow, dickcissel, burrowing owl, lark bunting,
bobolink, ferruginous hawk, prairie falcon, upland sand-
piper, McGown's longspur, chestnut-collared longspur,
columbian sharp-tailed grouse, long-billed curlew, swift
fox, prairie dog, black-footed ferret, and pygmy rabbit.
the adverse effects of fragmentation are most severe
during the inevitable episodes that lead to other stresses,
such as drought, severe winters, high levels of predation,
and avoidance behavior when humans or predators are
present. even fires, beneficial for maintaining biological
diversity since prehistoric times, can be detrimental if
they further fragment an already marginal habitat. Habi-
tat fragmentation can push animals into places where
they encounter excessive competition from others already
there, or to habitats that are marginal, which reduces the
likelihood of survival during inevitable difficult times.
Roads, rural subdivisions, timber harvesting, and
energy development are common causes of habitat frag-
mentation and warrant further discussion (fig. 18.5).

to illustrate, elk and mule deer in shrublands tend
to stay about 1.5 miles away from roads in summer,
when traffic is greatest, and about 0.75 miles away
from roads in winter . 9 Much of their time is spent in
roadless areas. Similarly, sage sparrows and Brewer's
sparrows tend to avoid roads and oil wells by about
300 feet, and sage-grouse by 2-3 miles. Roads also are
pathways along which invasive plants become estab-
lished and expand.
other effects of roads include direct mortality from
collisions. the number of animals killed by vehicles is
small compared to fatalities from inadequate food sup-
ply and hunting, but large ungulates on the highway
are genuine traffic hazards for people. Also, crossing
busy highways is one added stress that diminishes the
energy in body fat required for surviving the winter. if
energy reserves are insufficient, the animals are unable
to return to their summer range, where their reserves
are normally restored (see chapter 15).
the best-known example of road effects on ungu-
lates is at trapper's Point, along U.S. Highway 191 west
of Pinedale. this highway intersects the fall migra-
tion route of pronghorn from Jackson Hole and Grand
teton national Park up the Gros Ventre River valley,
across the divide to the headwaters of the Green River,
and then southward along the Green River valley to
the sagebrush steppe south of Pinedale and east of Big
Piney—the longest known migration of a mammal
in the contiguous United States. if they survive, the

Roads
the very presence of roads reduces the amount of hab-
itat far more than the area required for the roadway.