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Study Area

Elk Population

Population Dynamics

Elk Habits

Effects on Habitats

Elk Management






Research Report GRTE-N-1
The Elk of Grand Teton and Southern Yellowstone National Parks
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A 5-year field study was conducted in and adjacent to Grand Teton and southern Yellowstone National Parks. Objectives were to obtain reference information on the habits, population dynamics, and ecology of elk; and evaluate management programs. The two parks provided spring, summer, and fall habitat for the greater portion of the studied elk population which wintered on the National Elk Refuge immediately south of Grand Teton. The study area extended about 55 miles northward from the refuge's south boundary into the mountain and plateau regions of southern Yellowstone Park. Vegetation on the area was classified. Successional relationships were diagramed. The area's history from a summer hunting ground for Indians, through fur trade, settlement, and agricultural eras to the development of tourism was reviewed.

The elk wintering on the refuge were part of the Jackson Hole herd which historically wintered within and adjacent to extensive valley lands north and south of the refuge and the adjoining Gros Ventre and Buffalo river drainages. Early records suggest this herd contained up to 20,000 animals and was distinctly separate from elk which wintered in the Green River drainage. Migration and distribution studies indicated that about 29 percent of the elk wintering on the refuge summered in Grand Teton; 42 percent, in southern Yellowstone Park. Most of the remainder summered over extensive national forest lands adjoining the two parks. A resident summer herd of over 1,000 animals became established within Grand Teton valley areas that had been closed to hunting for about 10 years. Examinations of reproductive organs suggested that about 89 percent of the female elk older than yearlings became pregnant. Mortality of newborn calves probably averaged about 60 percent. Differences between reflected annual increase rates by calf proportions in winter herds, their realized recruitment as yearlings, and "best fit" comparisons of calculated herd sizes with periodic censuses suggested that a combined 2 to 3 percent mortality of calves and adults occurred during and after most winters of average severity; at least 15 percent during and after more severe winters. Overwinter mortality that averaged about 5 percent over mild, average, and severe winters was probably partially density-independent within the range of population size accommodated by variable environmental conditions.

Census records for 57 years since 1911 showed relatively "stable" population trends for the herd wintering on the refuge. Winter numbers fluctuated within a 6,000-8,000 range about 65 percent of this time, a 5,000-9,000 range 78 percent of this time, and a 5,000-10,000 range with a 98 percent frequency. Fluctuations showed no obvious relationship to hunting removals until after 1950. Elk numbers for the Jackson Hole herd as a whole declined about 30 percent over the 57-year period. Declines mainly occurred in herd segments that had substantial portions of their winter range appropriated for human settlement and agriculture, or in groups that wintered off the refuge on smaller state feed grounds established to reduce elk conflicts with agriculture. Overall declines coincided with an approximate loss of one-third of the herd's original winter range and substitutions of livestock for elk grazing on other wintering areas.

Dispersals to spring ranges on Grand Teton usually occurred during the first half of May. The use of different areas for calving and rates of migration to Yellowstone summer ranges were variably influenced by snow accumulations in mountain passes. Progressive movements from low to high elevations on summer ranges usually occurred to about late July. Differences occurred with sex and age, parous and nonparous females, and molesting insect activity. Reverse movements usually started in August. Marked animals showed elk from widely separate winter herds were intermingled on Yellowstone summer ranges. Interchanges of animals between winter herds were limited. Records from fall migration studies showed that elk groups that summered in and/or migrated through more accessible hunting areas outside Grand Teton boundaries progressively declined through the 1950's. Increases occurred in groups summering in national parks or migrating through less accessible hunting areas outside parks.

Relative use of different habitats was shown by observation samples of 82,223 elk in valley areas and 20,017 in mountain areas. Use of bunchgrass-shrub, sagebrush, valley meadow, forest, and agricultural types averaged 30, 29, 21, 17, and 3 percent, respectively, for April through December periods in valley areas. Use of forest, herbland, forest park burn, valley meadow, and subalpine meadow types averaged 37, 30, 16, 9, 6, and 2 percent, respectively, for June through October periods in mountain areas. Differences occurred with seasonal periods and years.

Food habits information was obtained from 262,602 instances of recorded plant use at 473 elk feeding sites. An average yearlong food habit of about 51 percent grass and grasslike plants, 26 percent forbs, and 23 percent shrubs was calculated for free-ranging elk. Differences in forage class and plant species use showed elk were extremely versatile and generalized feeders with a capacity to contend with a wide spectrum of environmental change. Vegetation measurements showed elk maintained biotic disclimaxes on limited ridgetop and upper slope sites that were kept free of snow by wind or first thaws. Variable snow conditions and the foraging actions of the elk themselves appeared to prevent the animals from progressively depleting their main food sources on bottomland, upland swale and slope areas that were usually snow covered from November through March. The animals hastened the replacement of seral willow or aspen when stands reached late successional stages or remnant status. Elk effects which represented a departure from natural relationships appeared to be limited to wintering areas within 1 mile of feed grounds, Measurements of elk and other biotic effects on spring and high elevation summer ranges suggested these were limited or of a temporary nature and did not represent departures from natural relationships.

Accumulated information from elk distribution and migration studies led to specific objectives for cooperative State and Park Service management programs after 1963. Long-term objectives were to restore historical distributions and migrations that had been altered by unequal hunting removals and reduce the need to hunt elk in Grand Teton Park. Specific short-term objectives were to halt October migrations of Grand Teton summer herds to refuge winter ranges, reduce late migrating Yellowstone elk groups that had increased during the 1950's, and allow compensating increases in other groups that summered and/or migrated through areas outside park boundaries. October migrations were largely halted after 1964. Management programs that involved the use of split hunting periods, special permit areas, and kill quotas for different herd groups appeared to start trends toward accomplishing distribution and/or migration changes after 1963.

A section on ecology integrates study findings into an overall account of suggested relationships within and between the elk population and its environment. Climate, winter weather and food, plant succession, predators, scavengers, parasites, disease, and man are related to the elk as environmental influences. Artificial feeding was suggested to have population consequences to the extent that it did not provide net gains in energy over what calves and pregnant females would obtain by freeranging. Considerations of elk behavior indicated that the animals influenced their own distributions in the absence of overriding environmental influences. Social disorder on feed grounds and conservation of energy relationships are discussed. Interpretations of elk habitat relationships required considerations of natural selection and plant successional processes, the ecological completeness of winter habitats, and distinctions between food sources that did or did not have population consequences. Intraspecific competition for food and environmental influences from winter weather, predators, scavengers, and disease were considered to represent the natural regulatory complex on presettlement elk populations. The regulation of present populations differed to the extent that man increased or decreased the intensity of natural regulatory influences and substituted himself for the original predator-scavenger fauna. Density-independent mortality precluded maintaining highly stable elk numbers and fully substituting hunting removals or artificial feeding for all severe weather influences.

Man's hunting appeared more efficient than original predator scavenger complexes in reducing extreme fluctuations in elk numbers. It was less efficient in allowing the elk population to maintain its numbers and distributions in relation to suitable habitats and available food sources. Purposes of the two national parks and other cooperating agencies are discussed relative to the studied elk population. Cooperative management programs to restore historical distributions and migrations are expected to progressively reduce the need for large scale hunting within Grand Teton and obtain desired elk kills by recreational hunting outside park boundaries.

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Last Modified: Tues, Jan 20 2004 10:00:00 pm PDT

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