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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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Behavior Relationships

Behavior that appeared to be caused by external environmental influences or relationships within the elk population itself is listed in Table 27. Spring dispersals off feed grounds, November migrations that occurred with particular snow conditions, and aggregations of animals into large groups on refuge feed grounds appeared to be food-linked responses.

Movements off the refuge to Grand Teton spring ranges and into Yellowstone Park seemed initially to be a response to reduced environmental resistance; by mid-May, some overriding attempts by females to reach calving areas. These, the dispersals off feed grounds and November migrations, tend to show behavior that resulted from a progressive relaxing and return of severe weather conditions that influenced the availability of food or restricted movements along a general elevational gradient (the Snake River drainage). It appeared that elk would remain in scattered distributions on summer home ranges in the absence of weather conditions that reduced the availability of their food. Weather severity along elevational gradients resulted in the animals moving to and concentrating on lower elevation areas where essential members of the population survived the severest winters. Moderating weather allowed reverse movements and a return to scattered distributions on summer home ranges.

Table 27.—Summary of elk behavior caused by external environmental influences and intraspecies relationships.

BehaviorIndicated causes

Spring dispersals off refuge feed grounds Moderating weather exposing snow free areas and initiating new grass growth.
Movements off refuge to Grand Teton spring ranges Moderating weather reducing snow depths which restrict movement or, by mid-May, attempts by females to reach calving areas.
Variable use of calving areas and rates of movement through mountain areas Variable late May-early June snow conditions in mountain passes.
Delayed movements of female/ calf groups onto high elevations Initial care-dependency relationships between female and young.
Mid-summer aggregations on high elevation ranges Molesting insects.
August dispersals from high ranges into forest types Female avoidance to early sex-linked behavior of adult males.
Mid- to late October movements of some elk to refuge wintering areas High levels of human disturbances on Grand Teton fall ranges that have limited escape cover for large elk groups.
November aggregations and migrations from mountain areas Snow conditions restrict access to food along an elevational gradient.
Rapid and direct movements over valley early winter range areas to the south half of the refuge Human disturbance and hunting in areas with limited forest cover.
Aggregations of large groups of elk on small feed ground areas Conditioned habitual use of easily obtained hay diets by adult animals and leader-follower relationships.

Delayed movements of a portion of the elk population onto high elevation ranges, August dispersals into forest types, and the formation of harem groups represented behavior linked to reproduction. Newborn calves delayed the movements of maternal females and other associated animals to the most distant Yellowstone summer ranges and to high elevations until July. Subtle attempts by previously segregated adult male elk to associate with groups of females and calves (observed as early as August 9) contributed to breaking up summer group associations and caused dispersals into forest types. Overt displays by adult males and attempts to collect females in harems (rutting behavior) were observed as early as August 13 and commonly after this date. Field records showed all male elk older than yearlings had started or completed removing the velvet from their antlers by August 25. The process was observed to start as early as August 13. Attempts to hold females in harem groups appeared to be most successful between mid-September and mid-October. Over the mid-August through October period, the size of elk groups in mountain areas averaged about six animals (N = 4999). Yearling males were usually excluded from harem associations of females and calves that were attended by an adult male.

Classifications obtained by Martinka (1965) showed late August through October group sizes in valley areas were much larger, averaging about 30 animals (N = 12,936). An average group size of 11 animals was observed during the mid-September to mid-October peak of breeding activity. These higher group sizes probably resulted from fewer adult males being initially present in valley areas and a greater tendency for harem groups to aggregate on extensive fall range areas with limited forest cover.

October migrations of Grand Teton elk to refuge winter ranges appeared to represent behavior responses to viewing by park visitors and some illegal hunting disturbances on large elk groups (200 to 500 animals) within low security level habitats (outwash plain with limited forest cover). After 1964, old roads within the western portions of Grand Teton were closed to provide blocks of fall range where large elk groups could be seen from vista points, but not disturbed by too close an approach. These roads had either penetrated major fall range areas for large elk groups or allowed untolerated approaches between foraging animals and their forest cover. The road closures, in combination with limited permit hunting on eastern portions of Grand Teton and the National Elk Refuge, greatly reduced early October migrations from the western portions of the park.

As discussed in the Habitat Use section, aggregations of large numbers of elk at high elevations in mountain areas were caused by molesting insects. The equivalent behavior response for elk in Grand Teton valley areas or in groups scattered at low elevations within mountain areas was to retire into forest types or bed in dense herbaceous vegetation in meadows. This would suggest that high elevations were not a deciding or critical factor in the animals' establishment of summer home ranges. Brazda (1953) sampled molesting insect densities which indicated elk would obtain greater relief at high than low elevations. An additional relationship may have been that large aggregations of elk afforded relief. Allee et al. (1959) cites an account that aggregations of at least 300 to 400 reindeer (Rangifer sp.) permitted herds to remain intact under warble fly attacks.

The suggested relationship was that elk largely influenced their own scattered distributions when environmental stresses were minimal. These were variably maintained by matriarchal care-dependency and leader-follower associations with a dominant female elk; by mutual avoidance, subtle and overt agonistic behavior that maintained dominance subordination relationships within and between associations; and by sexual relationships between adult males and females. The latter involved either mutual or female avoidance behavior during periods other than the breeding season. Terminology follows Etkin (1964).

Aggregations of elk from scattered summer distributions and fall migrations occurred in relation to overriding environmental influences and coincident subjugations of some dominant females into leader-follower relationships. Subjugations may have resulted from some lessening of female dominance apart from home range "territories" used for the care of young. Aggregations of female and subadult elk on wintering areas apart from feed grounds probably re-formed as variably sized matriarchal associations with both care-dependency and leader-follower relationships. These re-established social order with energy conserving dominance-subordination (peck order) relations. Off feed grounds, adult males usually wintered in loosely organized herds socially apart from matriarchal associations. Such segregations of adult male elk apart from groups of females, calves, and yearling males were apparently the rule in early day elk populations (Preble, 1911).

Large groups of female, subadult, and adult male elk on feed grounds appeared to represent aggregations where social relationships progressively deteriorated. This may have resulted from daily occurrences of agonistic behavior between large numbers of variably dominant and subordinate elk on feed lines. The establishment of energy conserving peck orders was precluded and led to an early dissolving of maternal care-dependency relations (see Artificial Feeding). Moderating environmental conditions in spring, in combination with the re-establishment of maternal-care relationships, led to the re-establishment of scattered distributions on summer home ranges.

Aggregations of social groups did occur from foraging encounters on other than wintering areas. These were usually temporary or occurred under conditions where close crowding to obtain food was not necessary. Aggregations from escape encounters occurred in response to varying intensities of human disturbances and molesting insects. Male sexual behavior appeared to cause dispersals from aggregations and either temporary or lasting disruptions of summer matriarchal associations.

Habitat Relationships

Elk have apparently persisted for thousands of years in the Grand Teton and Yellowstone regions over a wide range of environmental changes which are still occurring. Vegetation changes have been short term and cyclic from fire, biotic influences, and variable growing conditions; or directional from developing soils, stream cutting, and climatic change. Selection pressures for the "most fit" plant and animal species have undoubtedly occurred and will continue. It seems unlikely that elk would have persisted if the animals were able to progressively deplete their main food sources which, in combination with other influences, determined their numbers (i.e., had population consequences).

Winter habitats that were interspersions of different physiographic sites and/or vegetation types provided increased opportunities for an elk population to remain in some dynamic balance with its food sources (homeostasis). These ecologically complete habitats had carrying capacity relationships where "the whole was greater than the sum of its parts." The elk's variable use of different habitat units, general food habit, protection from snow, and the capacity of native plants to withstand periodic heavy use appeared to preclude free-ranging animals from progressively depleting their main winter food sources. The density-influenced mortality of animals with low energy reserves also helped to maintain elk populations in balance with their food sources (see Population Regulations).

As biotic agents, elk influenced the rate at which late stages of seral vegetation were replaced, maintained relatively stable biotic disclimaxes on limited sites where their effects were either without population consequences, or were incidental to the use of food sources that had population consequences. They also occurred in some dynamic relationship with other native herbivores through "exclusion" or interspecific competition that retained a mixed species fauna within different food or habitat niches.

Exceptions to these apparently natural relationships occurred on upland areas adjacent to refuge feed grounds and wildlife wintering areas additionally grazed by domestic stock. Here, animal concentrations and/or consistent heavy or dual use of vegetation appeared to intensify disclimax conditions or cause seral vegetation to be replaced at a faster than "normal" rate.

These interpretations of free-ranging elk relationships to their winter habitats may only apply to other areas with equally variable and rigorous winter weather. They would have limited to almost no application where human influences restricted or precluded elk from using portions of a winter habitat (e.g., bottomlands, slopes, etc.) which were essential to homeostasis. What may be shown is that interpretations of elk habitat relationships require considerations of natural successional processes, the ecological completeness of winter habitats, and distinctions between food sources which do or do not have population consequences. Natural biotic effects or sucessuccessionalges would not require corrective management within a national park.

Population Regulation

The logistic curve relationship between population growth and environmental resistance may have been first expressed by Verhulst in 1883 (Allee, et al. 1949). Accumulated knowledge since this date further establishes that animal populations occur in some equilibrium (mean numerical stability) in the absence of environmental changes that consistently cause more or less resistance to population growth. Environmental changes which consistently offer less environmental resistance permit upward trends in population numbers. Consistently more environmental resistance results in downward population trends.

A regulating influence was considered to directly or indirectly cause deaths, or change population reproduction, or survival rates. The complementing influences from some animals emigrating from or immigrating into a population is recognized. The probable regulatory process for past as well as present populations is presented for comparison purposes.

Past Populations

Accumulated knowledge on the organization of life in natural communities tends to assure that past elk populations were regulated to the extent that they could not, by themselves, progressively deplete food sources which limited their numbers. This study suggests that the animals could have temporarily reduced the amount or quality of their own food sources as part of a natural regulatory process, reduced or maintained some food sources that did not limit their numbers as natural biotic disclimaxes, and accelerated late stages of plant succession to either increase or decrease their total food supply.

Intraspecific competition for available food and environmental influences from winter weather, predators, scavengers, and diseases probably interacted to lower the numbers in early-day elk populations in the following manner: When populations were at upper levels in relation to their available winter food, intraspecific competition intensified energy stresses. These stresses directly or indirectly caused the deaths of elk with the lowest energy reserves and sometimes lowered the subsequent year's reproductive success. The deaths of diseased and other energy-stressed animals were hastened by the combined effects of predators and scavengers.

Severe winter weather per se periodically caused higher than usual deaths, or what could be considered additional density-independent mortality, by increasing intraspecific competition, energy stress, and the efficiency of predators. These additional deaths were also animals with low energy reserves. Subsequent winters with less severe weather or intraspecific competition permitted elk populations to compensate for the deaths of animals with low energy reserves and return to higher numbers. Compensations resulted from increased reproductive success and survival or the process Errington (1946) calls "compensatory trends."

The reports of "high" winter mortality in the Jackson Hole herd at 4 to 6-year intervals during 1882, 1887, 1891, 1897, and 1911 (Preble, 1911; Anonymous, 1915; Sheldon, 1927; Brown, 1947) suggest that early day predator populations did not prevent the elk from contending with the regulatory influences from intraspecific competition for food or periodic severe winters. This should not be interpreted that predation on elk populations was without ecological significance. Original predator populations may have reduced the intensity of intraspecific competition within an elk population during more severe winters. The extent to which this occurred would have extended the interval between and dampened elk population fluctuations. The compensatory trend process (Errington, 1946) could be expected to compensate for periodically higher than usual mortality from predation.

Present Populations

Intraspecific competition for food and environmental influences from man, winter weather, a limited predator-scavenger fauna, and disease acted to lower numbers in present elk populations (Figure 16). The regulatory process mainly differed from that on past populations to the extent that man increased or decreased the intensity of natural regulatory influences. This resulted from his artificially feeding the animals, displacing the original predator-scavenger fauna, and changing herd distributions so as to reduce total food sources.

When elk on winter feed grounds were at upper levels (apparently a wide range) in relation to the available energy from their artificial diets and adjacent food sources or the effects of periodic severe weather, intraspecific competition increased energy stresses. These stresses directly or indirectly caused the deaths of subadults and older adults with the lowest energy reserves and sometimes lowered the subsequent year's reproduction. The deaths of diseased or energy-stressed animals were not significantly hastened by the remnant predator fauna which was mainly restricted to preying on newborn elk. Population increases back to higher levels, by compensating reproduction and/or survival, were influenced by hunting removals and other human influences.

The density-influenced or periodically higher density-independent deaths of animals with low energy reserves would not represent a loss of biologically essential population members and would be predestined to occur to the extent that elk populations were self-regulated (intraspecific competition) in relation to their available winter food. Such mortality would not occur to the extent that hunting removals could substitute for density-influenced deaths.

From 1962 through 1967 about 700 to 800 elk were estimated to consistently winter without using artificial food sources. These animals occurred in scattered distributions on historical winter areas on the refuge, Grand Teton Park, and adjoining national forest lands. Their numbers were variously regulated by interspecific competition, weather influences, hunting, and competition with domestic livestock. Small elk groups, that remained within Grand Teton areas closed to hunting or arrived on park winter ranges after hunting seasons were closed, were largely self-regulated by intraspecific competition for food and weather influences.

Generally high hunting kills from 1940 through the late 1950's coincided with progressive declines in the numbers of elk that freeranged off refuge feed grounds. This reduction in animals, which were partly or wholly on different food sources, may preclude presently distributed winter herds from reaching 1955-56 and earlier year population peaks of 10,000 to 11,000 animals. Sustained hunting removals that approximate herd increase rates and yearly artificial feeding may additionally restrict winter herd numbers from fluctuating outside the general 6,000 to 8,000 range that has prevailed over severe, average, and mild winters since 1961. Herds could be expected to occasionally fluctuate to higher levels with lower or less consistent hunting removals. The extent to which artificial feeding prevented subadults and/or other population members from freeranging in scattered distributions and obtaining more adequate diets could also restrict fluctuations to higher levels.

Man's actions in restricting elk from freeranging were not always unintentional when the animals' historical winter range was largely privately owned and used for livestock grazing or hay raising. Transfers of land, purchases, and administrative withdrawals have progressed to where the refuge herd could be allowed to freerange over a 60,000-acre block of this historical winter range. This could conceivably replace all artificial feeding.

Consistent artificial feeding of the refuge winter herd may result in a more apparent than real lowering of overwinter mortality rates by maintaining low proportions of vulnerable subadults in the population and only deferring until spring what Preble (1911) and others have considered "high" mortality from severe winters (about 15 to 20 percent of herd numbers, or a large portion of the calves). Comparable mortality of subadults and other elk with limited energy reserves appears to have occurred periodically over a wide range of population size up to the most recent severe winter of 1961-62. Such partially density-independent mortality would preclude maintaining highly stable elk populations.

If the present refuge herd was largely self-regulated as a result of low hunting removals and was not artificially fed, its winter numbers could conceivably fluctuate within a 5,000 to 9,000 range. If artificial feeding supplied more energy to subadults and pregnant females than they could obtain by freeranging (this needs to be demonstrated), the population might fluctuate within a 6,000 to 9,000 range; if it did not, a 5,000 to 9,000 range. The latter approximates the usual range of winter herd numbers that occurred before the higher hunting removals of the 1950's (Table 23 and Figure 8).

With hunting removals that attempted to reduce intraspecific competition by approximating average population increase rates, the winter numbers of a free-ranging herd might fluctuate between 5,000 and 8,000 animals. This compares with 6,000 to 8,000 fluctuations between 1961 and 1967 which may or may not have been maintained at higher levels by artificial feeding. These figures should be considered approximations which are mainly used to illustrate suggested relationships. Fluctuation ranges could vary with unusual sequences of winter weather, variable hunting removals, or changes in artificial feeding practices.

Man's hunting since 1955 appears to have become somewhat more efficient than original predator-scavenger complexes in preventing extreme fluctuations in elk numbers. It has not prevented the elk population from being additionally regulated by periodic severe weather and intraspecific competition. Complete substitutions of hunting for all natural mortality do not appear possible because severe weather influences on the availability of food and on subadult elk or other animals with low energy reserves were not completely density-dependent within the full range of population numbers accommodated by variation in the winter environment.

Man was obviously less successful than the original predator fauna in allowing the elk population to maintain its numbers and distributions in relation to suitable habitats and food sources. This resulted from his more efficient and less restricted (to predisposed and vulnerable elk) hunting reducing elk population groups that used particular habitat areas and forage sources. Conditioned avoidance behavior appeared to additionally restrict elk from using extensive wintering areas with abundant forage sources.

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

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