Research Report GRTE-N-1
The Elk of Grand Teton and Southern Yellowstone National Parks
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ECOLOGY
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.
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Behavior | Indicated causes |
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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. |
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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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