Wildlife Dimension of Elk Management
Elk and Brucellosis
Natural History of Elk
Herd Structure of Elk
it comes to elk management, one of the many challenges park managers
face is Brucellosis. In
the 1930s it was first discovered that elk herds in Yellowstone
National Park and at the National Elk Refuge in Wyoming carry
the disease. The problem lies in the fact that ungulates
in the Greater Yellowstone area (primarily bison and elk) pose
the risk of spreading Brucellosis to cattle when they seasonally
migrate outside the park to seek better forage.
Although the transferring of the bacteria from wildlife
to cattle has been shown to occur in a laboratory setting, there
have been no documented cases of it actually occurring in nature.
is a bovine-related disease that is caused by transmission of
the bacteria Brucella abortus. It is transmitted by the ingestion of reproductive fluids from an
infected female, and causes females to spontaneously abort their
fetuses. In the Greater Yellowstone area, it is carried
by both bison and elk. Both
species experience the same effects of the disease, but at different
rates. In studies done
by the Wyoming Game and Fish Department, it was found that when
inoculated with the disease, elk experience a 50%-70% abortion
rate while bison experience a 100% abortion rate.
Because transmission is more likely to occur from late
pregnancy to several weeks after birth, they also experience different
periods of possible transmission. For elk, the period of possible transmission
is between February and mid-June.
For bison, that period is slightly longer.
For detailed information on the effects of Brucellosis,
Transmission at the
is believed that in Wyoming, Brucellosis is limited to the elk
in the western part of the state, near the feeding ground complex. There are 23 elk feeding grounds in the state
of Wyoming that feed an average of 22,000 elk. Feeding grounds are where elk migrate to in the winter season when
forage is limited and where they are supplemented with food from
park officials. The general
purpose of feeding elk in a time when food is generally limited
is to reduce winter mortality and increase the hunting stock.
Elk at these grounds are highly concentrated and are therefore
at increased risk of transmitting Brucellosis, especially since
females are late in their pregnancy during winter.
Therefore, feed ground elk have a high rate of infection. The disease has been detected by blood tests
in 18 of these feeding grounds (equaling about 18,000 elk). At highly infected feeding grounds, elk herds
may lose up to 12% of their reproductive potential. To make matters worse, it didnt take
long for bison to discover the feeding grounds.
Bison commonly feed at the grounds, thus increasing their
chances of getting infected with the disease.
Why are bison more
of a concern than elk?
bison and elk both carry Brucellosis and both can transmit the
disease to cattle, bison have become more of a concern. More time, money, and effort has been put into
preventing infected bison from entering cattle grounds and ranches
surrounding the Greater Yellowstone area.
A few reasons for this are:
have a longer period of possible transmission because of longer
breeding and calving periods.
have a higher abortion rate than elk when artificially inoculated.
herds experience more contact with each other than elk herds,
especially during pregnancy, birthing, aborting, and calving. Brucellosis is more readily transmitted.
are less effective in bison than in elk.
have a higher economic value (due to hunting)
people may think that because bison
look more like cattle than elk do, they have a higher
chance of spreading it to them.
The livestock issue
ranchers surrounding the Greater Yellowstone area are concerned
that bison and elk will transmit Brucellosis to cattle when they
wander outside the park. Usually
bison and elk do not come in close contact with cattle, but because
the disease is transmitted through reproductive fluids, they can
still pose a risk. Fluids containing the bacteria can last for
several days and even though the infected female may not be present,
she may have left behind fluids on the ground or hay for a cow
to later ingest. However, transmission of Brucellosis to cattle
is highly unlikely and there have been no documented cases of
it occurring. But this
is not to say that it cannot happen.
Among cattle the disease is transferred more readily.
Therefore, infection of just one cow may lead to infection
of the entire herd, which could have serious impacts for not only
the individual producer, but also the entire livestock industry
for that state. A states loss of Brucellosis-free
status can have serious economical
What is Being Done?
has been developed for preventing Brucellosis transmission in
elk. The vaccine is injected
via darts to female elk at the feeding grounds, and works to reduce
abortions in elk and to reduce transmission rate as well as increase
individual resistance to the bacteria.
Calving success for a vaccinated elk is double that of
an unvaccinated elk. However, it will take several years for the
vaccine to significantly reduce Brucellosis in elk herds. This is because the vaccine has no effect on
animals that are currently infected.
Because the lifespan of an elk is relatively long, it may
be several years before all infected individuals are eliminated
from the population. The goal of the vaccination program is to obtain
at least a 90% vaccination rate.
Expected results would be increased calf production in
previously infected feed grounds and also significant reductions
in transmission of Brucellosis to cattle.
effective vaccine has yet to be developed for Brucellosis control
in bison. To find out
whats being done to prevent bison sources of transmission
to cattle, click here.
History of Rocky Mountain Elk
are the largest members of the deer family who are genus Cervus
and species elaphus. A full grown male, elk referred to
as a bull is comparable in size to a horse measuring five feet
tall and weighing up to eleven hundred pounds. Female elk are
referred to as cows and though may be comparable in size to bulls,
usually are shorter and weigh less.
Elk are ungulates,
which is the Latin word for hoof and referrers to animals with
hoofs. Hoofed mammals are divided into two different orders,
classified by their number of toes. The Artiodactyls are
those with an even numbered of toes such as elk, deer and bison,
where the Perrissodactyla are those having an odd number
of toes such as horses and elephants.
Mountain Elk Life Cycles
Elk are mammals driven
by instinct. Instinct is something that compels a species to
partake in activities that eventually promote their survival and
reproduction. Instincts that promote elks reproductive
fitness include seasonal movements, choice of calving grounds,
the selection of social groups and areas for feeding and resting.
With a life, which is estimated between eight and twelve years,
elk are part of many processes that through instinct propagate
their species survival.
Each spring, increasing
daylight hours elevates the hormone testosterone in male bulls.
The increase of testosterone in their bodies prepares their bodies
for the upcoming mating season. One of the first physical signs
that reveal the bulls preparation for the mating season is the
growth of antlers, which begin bony bumps on the male elks
skulls. Antlers grow succeeding larger as a bull matures. The
antlers complete their growth and in September. At this time
the velvet, which supplied the growing antlers with blood and
nutrients dries up and is rubbed off against trees and brush.
By rubbing off of the velvet, the antlers become ready for display.
A second year bull usually has un-branched antlers called prongs,
where a mature bull can have eight or more branches on his antlers,
with a spread of four feet and weighing up to forty pounds. Intense
feeding coincides with this time of year as fat reserves are reestablished
and migration toward the more nutritious food in the higher elevations
Cows often begin their
migration before they give birth, which generally coincides with
when the most nutritious food is available. The young are born
in mid May through early July, depending on where the elk live.
When a cow is ready to give birth, she leaves the herd and rejoins
in a couple weeks once the calf is strong enough to keep up with
the herd. During the spring and early summer, as new shoots, leaves
and buds of many plants emerge elk can move appreciable distances
in search of the new highly nutritious plant growth.
Rut and Harem Structure
In Autumn after a summer
of intense feeding the elk mating season referred to as the Rut
begins. At this time the animals move to lower elevations, segregate
into separate groups and establish mating groups called Harems.
A harem is usually established during the months of September
through October and mature bulls move in among groups of cows
and calves. Harems are usually smaller than the large cow and
calf herds of the summer as well as lack the male yearlings who
are driven off by more mature bulls. Younger bulls are able to
bread by their second summer and often try to enter the harems,
but seldom get a chance due to competition by bigger bulls. The
biggest bulls in peak physical condition ranging from about six
to eight years old are the individuals who usually take charge
of the harems.
To show their dominance
elk also bugle. A bugle is a high pitched whistling followed
by grunts that allow a bull to let his presence be known. As
a bull gets older, his bugle gets louder and more intense. This
allows a bulls size to be recognized through his bugle and
solicits his presence. Bulls also show off their antlers and bodies
to each other, sizing up each others fitness and ability
to defend their right of mating. Bulls also engage in strength
battles with each other to prove dominance and strength by locking
antlers and shoving each other back and forth. Young males usually
retreat upon an encounter with a mature bull, since their chances
of winning such a battle are slim. On the other hand, bulls equal
in size typically confront one another and display their dominance
by bugling, thrashing the ground with their antlers and finally
ensnare each others antlers and impel each other. Fighting is
a show of strength, not a battle to the death, and is done for
the ultimate reason of mating.
Once a bull has shown
his dominance, and has control of a harem he anticipates receptive
cows. A cow is receptive for mating less than twenty-four hours,
so when she is estrus, or in heat, the bull elk must be alert
and ready since the cow wont be willing to mate again until
her second, third or fourth estrus cycle, which are twenty days
apart. Once the mating is complete, the rut comes to an end.
At this time harems disband and the cows regroup. Bulls of all
ages once again gather together in bachelor groups and dispersing
from the females until the next spring. For the remainder of
the fall, both sexes resume eating while they prepare for the
Winter is a time of
limited food resources and harsh weather conditions. During this
time elk herds devour exposed vegetation, which often is limited
by the depth of snow. When the snow gets too deep and the weather
becomes too harsh fat reserves gained in the spring and summer
are used to survive.
The mortality of herds
is usually large this time of year, but is often dependent upon
the severity and length of the particular winter. The extreme
conditions of winter usually eliminates the weak, young old and
malnutitoned individuals first, leaving the healthier ones for
the coming year.
b) Movement and
Elk occur widely but
not uniformly throughout habitats. The presence, absence and
abundance of elk in various locations are determined by many factors.
Among the more important factors of elks location are the amount
of moderately level and low-elevation habitats present, the availability
of preferred food plants, the timing and severity of storms and
the depth and persistence of snow. Elk distribution also tends
to change over time, as vegetation changes due to natural disturbances
such as floods and fire, as well as human disturbances. Though
elks movements can vary from year to year due to the above
factors, elk typically follow a seasonal pattern of movement inhabiting
lower elevations in the winter and higher elevations in the summer.
Lengthening days, warming
temperatures and melting snow are all signals that trigger the
start of the spring movement for elk. As the snow begins to melt
in the lower elevations, elk progressively migrate to higher elevations
discovering the newly exposed fresh vegetation. The migration
from the lower elevation to the higher elevations that transition
the elk from their sparse winter diet into their intense summer
feeding, varies in length. The length of the migration depends
on where the elk live and the present food potential in their
current location. The actual migration can range from a few days
to a couple of months. During this time elk eat an extraordinary
amount of food, as they replace their depleted fat reserves from
the previous winter. Consuming up to fifteen pounds of vegetation
daily an elk spends the majority of its time eating while present
on their summer feeding grounds.
In autumn after a several
months of intense feeding in the higher elevations, falling temperatures,
snow piling up in the high country and more frequent storms signal
the elk to leave their summer range in the high elevations and
begin their decent to the lower elevations. In the lower elevations
the elk encounter their winter range. The winter range is where
the elk reside until warmer temperatures call them back to the
higher country. On the winter range, the elk try to locate areas
with less snow or no snow at all where food is easily accessible.
In the winter elk usually eat less and rest more. Two popular
theories explain this behavior. One theory consider less movement
and more rest as a means of conserving energy, while others believe
that since the food consumed in the winter is tougher for rest
is required for digestion.
c) Habitat Requirements:
Animals require food,
water, shelter and space to suit their specific needs. Elk also
require these things, which will be discussed below.
An elk, like any member
of the deer family is an herbivore. An herbivore is one whose
diet is composed entirely of vegetative material. Though elk
only consume vegetation, they are quite selective of the parts
that are taken from each plant. Most elk consume the entire growth
of grasses and herbs, but only select the fronds and leaf tips
of ferns, the fallen leaves of such trees as red alder, and the
soft terminal branching and needles of a hemlock tree. Broad
descriptions of the vegetative material elk consume include various
grasses, leaves, shrubs, trees, twigs and bark. These materials,
which are often tough and fibrous, require a special type of stomach
to digest, process and extract the essential nutrients within.
Elk have a multi-chambered stomach that digests, processes and
extracts these essential nutrients within by having the food they
eat go through various phases of digestion, which turns their
food into the nutrition they require for life. Though nutrition
is key, it is also critical that elk have water. Elk have many
uses for water including cooling themselves off and aiding digestion.
Elk usually are drawn to wherever water is accessible, which can
be at various water hole, lakes, creeks and springs. If no water
is available, elk become very resourceful in obtaining the precious
life juice. In the wintertime when water is scanty because of
the freezing temperatures, elk obtain water by eating snow.
An elk with plenty
of food and water are not complete. Elk need shelter. During
winter storms and flooding, elk often move away from the colder
and more hazardous river bottoms to the denser and more protective
forest canopies. This type of shelter protects elk and other
animals from the elements, providing a break from the wind, holding
warmth in and catching much of the snow before it hits the ground.
While protecting a herd from the elements, a shelter also gives
elk a place to avoid and hide from predators, allowing a greater
survival rate of individuals from being consumed.
Like every animal,
elk require room to roam about away from particular confined parameters.
Elk usually ramble around a home range, which in the summer time
consists of about two square miles, and in the winter about eight
square miles. Though these are average parameters elk are capable
of trekking more than fifty miles in a day and the distance they
travel is usually not the limiting factor.
c) Natural Predators
As a staple of many
predators diet elk can be consumed at various rates depending
upon the ecosystem. Elks main predators include black bears,
grizzly bears gray wolves, cougars, and mountain lions. If approached
by a predator a bull or cow may become aggressive with the individual
and attempt to ward them off. This behavior may be effective
for certain predators such as wolves, who will probably pick a
weak or sick individual upon an encounter with an aggressive elk.
If on the other hand a grizzly desires an elk, the elk has no
chance and can be easily pursued and destroyed.
Mountain Elk Federation
Structure of Yellowstone’s Elk
There are eight elk
herds, totaling approximately 120,000 elk, in the Greater Yellowstone
area. They are usually named after the geographic area they winter
in. The elk herds are named as follows:
- Northern Elk herd
- Clarke’s herd
- North Fork Shoshone herd
- Carter Mountain herd
- Jackson herd
- Sand Creek herd
- Madison-Firehole herd
- Gallatin herd
The elk herds of Yellowstone
are among the largest in the world. The smallest have approximately
650 animals (Madison-Firehole herd) and the largest have upwards
of 22,000 (Northern Elk herd). Most elk herds are migratory;
that is, they change their location (range) depending on the season.
In winter they occupy low elevation ranges where there is less
snow. As the snow melts in the spring, they migrate to their
higher elevation summer ranges. As the map
shows, most elk herds summer inside Yellowstone National Park
(YNP). It is estimated that there are over 30,000 elk that summer
inside YNP, and 15,000-22,000 that winter inside YNP.
The Northern elk herd
has been the basis of the controversial overgrazing issues that
YNP managers face. This herd is the largest of all in the Greater
Yellowstone area, weighing in at 15,000-22,000 members. Their
winter range (or “Elk Northern Range”) spans about 153,000 hectares,
of which 65% lies within YNP.
What Makes up a
Within a herd, there
are several subgroups, characterized as the following:
- Cow/calf herds –
In the summer, after calves have been born, several calves may
form smaller groups centered around a single cow (adult female).
This gives cows the advantage of having time to eat while leaving
their calves with a “babysitter” cow.
- Harems – In the
autumn, bulls (mature males) will join a group of cows and calves,
creating a harem. Harems are generally smaller than cow/calf
herds. Yearling males do not participate in harems, as they
are chased off by mature males. A bull will have 20-30 cows
in his harem and must compete with other males to have access
to his harem.
- Bachelor groups
– After the mating season ends, the harem separates. The cows
(likely now pregnant) regroup and bulls of all ages (including
the yearlings) gather to form bachelor groups. Both cows and
bachelor groups begin to migrate to their winter range, although
they often occupy different areas of the winter range.
The concept of natural
regulation is based largely on ecological terms such as equilibrium
and stability. Fluctuations in elk populations can occur
from variations in winter severity, quantity and quality of available
forage, emigration, hunting, and predation. A population is defined
as stable if it experiences these fluctuations and still returns
to a stable point, or equilibrium. For example, if a severe
winter results in die-off of a large proportion of an elk herd,
and that herd is able to increase reproduction back to equilibrium
numbers, then it is stable. Furthermore, stability can be either
local or global. A population is locally stable if it
returns to equilibrium after a small perturbation. It is globally
stable if it returns to equilibrium after large perturbations
in population numbers.
The Northern Elk Herd
It has been suggested
that the elk numbers on the northern range are globally stable.
They experience yearly variations in winter severity, causing
substantial fluctuations in abundance. After large deviations
from equilibrium, this herd always returns to its population equilibrium.
In addition, the concept of a dynamic equilibrium has been
used to describe elk on the northern range. This means that equilibrium
points are not constant through the years; they can change over
time. Equilibrium points can change depending on climate or environmental
influences. For example, an elk population’s equilibrium point
after a severe winter may be lower than after a mild winter.
Whether or not the
Northern Elk herd is globally stable or if they experience a dynamic
equilibrium has sparked much debate among wildlife managers in
YNP. Understanding how elk populations function is critical in
deciding how much of a role humans must play in managing the herds
to reassure their persistence to future generations.