More than 30,000 elk from 7-8 different herds summer
in Yellowstone and approximately 15,000 to 22,000
winter in the park. The subspecies of elk that lives
here are found from Arizona to northern Canada along
the Rocky Mountain chain; other species of elk were
historically distributed from coast to coast, but
disappeared from the eastern United States in the
early 1800s. Some other subspecies of elk still occupy
coastal regions of California, Washington, and Oregon.
Elk are the second largest member of the deer family
(moose are larger). Adult males, or bulls, range
upwards of 700 pounds while females, or cows, average
500-525 pounds. Their coats are reddish brown with
heavy, darker-colored manes and a distinct yellowish rump patch.
Bulls grow antlers annually from the time they are
nearly one year old. When mature, a bull’s "rack" may
have 6 to 8 points or tines on each side and weigh
more than 30 pounds. The antlers are usually shed in
March or April, and begin regrowing in May, when the
bony growth is nourished by blood vessels and covered
by furry-looking "velvet." Antler growth ceases each
year by August, when the velvet dries up and bulls
begin to scrape it off by rubbing against trees, in
preparation for the autumn mating season or rut. A
bull may gather 20-30 cows into his harem during the
mating season, often clashing or locking antlers with
another mature male for the privilege of dominating
the herd group. By November, mating season ends and
elk generally move to their winter ranges. Calves
weighing 25-40 pounds are born in late May or early June.
Climate is the most important factor affecting the
size and distribution of elk herds here. Nearly the
whole park - approximately 2.2 million acres -
provides summer range for elk. However, winter
snowfalls force elk and other ungulates to leave the
greater part of the park. Only the northern, lower-
levation portion of Yellowstone, where temperatures
are more moderate and snowfall less than in the park
interior, can support large numbers of wintering elk.
Annual precipitation, which occurs mostly as snow,
averages as high as 75" in the southern, high-mountain
plateaus of the park; minimum temperatures there are
often well below 0° F, and have been as low as -66° F.
In contrast, most of the northern range averages less
than 30" of precipitation annually, and winter
temperatures are considerably warmer.
The Overgrazing Controversy
National attention has been focused on Yellowstone's
northern elk winter range since the early 1930s.
Scientists and managers then believed that grazing and
drought in the early part of the century had reduced
the range's carrying capacity, and that twice as many
elk were on the range in 1932 as existed in 1914. From
1935 to 1968, elk, pronghorn, and bison numbers were
artificially controlled by shooting or trapping and
removal by park rangers. Then in the 1960s, based on
new studies that suggested ungulate populations could
possibly be self-regulating, elk reductions were
discontinued in the park. The belief that elk grazing
was damaging to northern range vegetation and that
grazing accelerates erosion, although not supported by
research data and analysis, has continued to the
present. Studies of the northern elk winter range
began in the 1960s and revealed no clear evidence of
range overuse (Houston 1982). More recent studies
conclude that sagebrush grasslands of Yellowstone's
northern winter range are not overgrazed (Singer and
Bishop 1990). In fact, plant production was enhanced
by ungulate grazing in all but drought years. Protein
content of grasses, yearly growth of big sagebrush,
and seedling establishment of sagebrush were all
enhanced by ungulate grazing. Neither reduction in
root biomass nor an increase in dead bunchgrass clumps
was observed. However, many questions remain
concerning the condition of riparian zones and
associated shrubby vegetation; the park hopes to
conduct additional studies on aspen and willows and
their relationship to ungulates on the northern range.
Two reports were made available in 1997, discussing at
length the issue of grazing levels and other
influences on Yellowstone's northern range.
Yellowstone's Northern Range: Complexity and Change in
a Wildland Ecosystem discusses the history of research
and management in northern Yellowstone, home to one of
the world's largest herds of elk and long the subject
of controversy. Effects of Grazing by Wild Ungulates
in Yellowstone National Park contains 22 technical
publications summarizing recent research studies that
have been peer-reviewed by scientists. Much of the
research was completed by scientists from agencies
other than the National Park Service, by independent
contractors, and by scientists from universities
located across the United States. For a copy of either
report, contact the Yellowstone Center for Resources,
Box 168, Yellowstone NP, Wyoming 82190, or call (307)344-2203.
Other Influences on Yellowstone's Elk Populations
Over-winter calf mortality, yearling mortality, and
adult bull mortality all increase with higher elk
population densities. Studies show that summer
predation by grizzly bears, coyotes, black bears, and
golden eagles takes an average of 32% of the northern
range elk calves each year. Mountain lions prey upon
elk, as do hunters north of the park (taking about 10%
of the northern herd annually through the 1980s).
Gray wolves, eliminated from the park by the 1930s,
are being restored, but not because park managers
think the wolves will "control" the number of elk.
Instead, 15 North American wolf experts predicted that
100 wolves in Yellowstone would reduce the elk by less
than 20%, 10 years after reintroduction. Computer
modeling of population dynamics on the northern winter
range predicts that 75 wolves would kill 1,000 elk per
winter, but that elk would be able to maintain their
populations under this level of predation, and with
only a slight decrease in hunter harvest. Since the
restoration of wolves to Yellowstone began in January
1995, scientists have begun to document the effects of
wolves on elk and other species. Wolves are preying
predominantly on elk, as expected. They have also
occasionally preyed upon moose, bison, deer, and even
one pronghorn antelope.
The carrying capacity of the northern winter range
increased in the 1980s because elk colonized new
winter range in and north of the park, wet summers
resulted in better plant production, winters were
mild, and the fires of 1988 opened forests allowing
more ground cover to grow. Since 1985, more than
11,000 acres of elk winter range have been purchased
by the State of Montana and the U.S. Forest Service
north of the park, increasing elk carrying capacity
and reducing conflicts between native wildlife and agriculture.
The Madison-Firehole Herd
The Madison-Firehole elk herd has been the focus of
research by Dr. Bob Garrott of Montana State
University since November 1991. This herd numbers from
650-850, and is believed to winter almost entirely
within Yellowstone Park. The population appears to be
naturally regulated to a degree not found in other,
human-hunted elk herds. The information resulting from
this research is useful in comparing unhunted and
hunted elk populations. Researchers examined the
effects of environmental variability on ungulate
reproduction and survival. Researchers also examined
elk use of areas burned in the wildfires of 1988.
Observations indicated that elk have made more than
casual use of burned trees; tests showed that fires
altered the chemical composition of lodgepole pine
bark, making it more digestible and of higher protein
content than live bark. While the burned bark was not
the highest quality forage for elk, it is comparable
to other low quality browse species. The researchers
speculated that elk select burned bark because it is
readily available above the snow cover in winter.
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