Mountain Wildlife - Mountain Geography: Physical and Human Dimensions - page 431

Nor can rock hoppers grow to very large size, as body size quickly thwarts accel-
eration, because acceleration increases as the square of linear dimensions, but mass
increases as its cube. Therefore, rock hoppers retain relatively small body size, or,
in growing large, replace rock hopping with cursorial (running) adaptations that may
serve them very well on open slopes away from cliffs (Geist 1998). Large body size, such
as in arctic musk oxen ( Ovibos moschatus ), or in the takin ( Budorkas takin ) from South-
east Asia, limits the species to rapid climbing in cliffs. They have short, powerful legs.
Cliffs offer not only gravity as a deterrent for predators, but also a quick loss of the
quarry from sight. Irregular cliff contours and crevasses may quickly hide the escaping
prey. Caribou, which are excellent mountaineers, have adapted as sophisticated cours-
ers that can sprint over open slopes and along ridges, following long, even trails that
generations of caribou have pounded into the scree and rock (Geist 1998). These level
trails, running largely parallel to one another, are readily seen and identified as caribou
country from the air. However, caribou can also climb in cliffs remarkably well and with
surprising speed.
A predator approaching a mountain ungulate on a steep cliff may be dislodged and
hurled away from the cliff face to its death. Mountain ungulates that turn and face a
predator may be preparing to suddenly dash between the predator and the cliff, dis-
lodging the predator and throwing it down the cliff. Mountain goats may turn and attack
a predator directly, using their great strength and very sharp horns to dislodge the wolf,
grizzly, wolverine—or a careless human hunter. Golden eagles ( Aquila chrysaetos ) no-
toriously dive at sheep or goats in cliffs, trying to snatch a lamb or kid, or dislodge an
adult that may then fall to its death. However, female bighorn sheep, standing protect-
ively over their lambs, tend to jump and butt at the eagles. One ewe connected, trans-
forming the eagle into a mass of broken bones and disoriented feathers that never flew
again (Geist 1971).
Small mammals escape predation by avoiding detection or by quick escapes into cov-
er, such as natural rock formations or burrows. Nevertheless, they may not be entirely
safe here, as grizzly bears will dig deep to reach marmots and ground squirrels fattened
for hibernation. The long claws of grizzly bears have apparently evolved as adaptations
for digging. Above ground, extreme vigilance is called for by foraging marmots, ground
squirrels, or chipmunks to evade eagles, falcons, and hawks. Some species, such as the
wood rat ( Neotoma cinerea ), appear only toward night under cover of darkness. The
cryptic coloration of the white-winged ptarmigan ( Lagopus leucurus ) in its summer or
winter plumage, testifies to the hazards of living above ground under the sharp eyes
of raptors, as does the explosive, quick, erratic, ground-hugging flight of the escaping
bird.
Body Size, Proportions, and Temperature
Temperature extremes give rise to diverse adaptations in large mammals with excellent
temperature regulation. Early observations on the effect of altitude and latitude on the
nature and distribution of animals advanced several correlates or climatic rules about
the response of warm-blooded animals to low temperature. One of these, the famous but
invalid Bergmann's Rule, states that the body size of similar species tends to increase
in colder climates, because relative surface area declines with body mass, thereby ex-