Predator and prey responses
to wolf reintroduction
Yellowstone pack morphology
The "gray wolf" actually occurs in several colors,
and the pelage of most wolves contains several shades of different
colors. Gray wolves range from creamy white all the way to inky
black. Pups from a single litter often show color variety, and wolf
packs include animals of all different colors. A lot like fish,
wolves are dark above and light below. A typical gray wolf has cream
or white legs and tan sides. The long black guard hairs on the back
and shoulders give wolves dark backs. The complex light and dark
shading on a wolf's face dramatizes its expressions, which is useful
for such highly social animals
Gray wolves are smaller than most people think. Most
weigh between 50 and 100 pounds, females about 20% smaller than
males. Size is related to geography. The wolves of some desert regions
may not exceed 45 pounds, and the Mexican wolf is small enough to
be mistaken for a coyote. However, weights of 115 pounds are not
uncommon for cold regions. The largest wolves come from Alaska,
the Yukon, some areas of Canada, and the former Soviet Union. Those
regions occasionally produce individuals weighing up to 175 pounds.
The length of a gray wolf are approximate to the height
of humans; they vary between five and six and a half feet long (nose
to tail tip). Of that length, about 18 inches is tail. Males usually
stand 26 to 32 inches at the shoulder females about 20% less.
The teeth of a wolf are its livelihood. There are
42 teeth which all serve a particular function. The four canines,
for which wolves are known, are usually over an inch long. Their
primary purpose is to pierce the hide and hair of various ungulates
and the like. This provides a sure hold as well when attempting
to take down a large prey species. The molars at the back of the
jaw have the power to crush even femoral bones. Between the molars
and the canines are the carnassial teeth, which shear skin, sinew
If the teeth of the wolf is its livelihood then the
senses of the wolf are its bread and butter. Vision primarily becomes
important to wolves during chases when prey is near. Wolves can
apparently detect moving objects at distances where they cannot
discern stationary objects. A wolf's sense of hearing is far more
acute than that of a human. A wolf's concave external ear funnels
sound vibrations to the inner ear and can hear howling as far as
six miles away, possibly up to ten. They can also discriminate between
tones that are very similar. Most biologists claim that wolves are
a hundred times better at sensing odors than humans, some even say
much more so than a hundred. Wolves can smell prey up to a mile
and a half away in a favorable wind. Of course there are odors wolves
can detect which we can't measure due to the fact we have no way
of knowing they are present, this is the crux of the wolf.
here to find out more about wolf biology and taxonomy.
Predator and prey responses to wolf
One of the major influences of re-introducing a large
predator on an ecosystem is the response of that predators prey
as well as other predators in the area. We will cover the primary
prey of wolves (Elk) and the primary competitive predator (coyote).
There are other predator and prey which are affected as well which
will also be covered.
Coyote- He used to be top dog, but no more...
Black bear- Do wolves have an adverse affect
on his omnivorous ways?
Grizzly bear- Is the "king" of Yellowstone still
the apex predator?
Mountain lion- Does this elusive cat interact with
Elk- Will wolves "wipe-out" the elk in Yellowstone?
Bison- How often do wolves actually hunt bison?
Mule deer- Are there enough to survive a high
Moose- Not to many in Yellowstone, how will they
Bighorn sheep- Not a traditional prey species
of wolves, will they be affected at all?
Pronghorn antelope - Can the wolves even catch
White-tail deer / Mountain goats- Some believe these
species won't experience any loss to wolves
Prey related to human
Cows- Are the predation numbers as high as everyone
Sheep- Is this a traditional prey species of wolves?
Domesticated dogs- Not a prey species, but
how have they been affected by the reintroduction?
Other possible prey species in the Greater
To see trophic effects of wolves on ecosystems
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The GYE coyotes seem to be the most affected by the
reintroduction of gray wolves. Prior to the reintroduction in 1995
coyotes displayed a pack structure of their own when they existed
at, or close to carrying capacity.
Coyotes were the number one predator of elk calves,
taking more than even mountain lions, black bears and grizzly bears.
This all changed when the wolves showed up in 1995.
When the first pack of wolves, the rose creek pack,
was introduced into their pens for acclimitization researchers and
observers noted many coyotes howling for over a half an hour. It
seems the coyote had an idea of what this apex predator meant for
In the five years since the reintroduction of the
wolves researchers have noted many changes in coyote life. The most
significant is the decrease of coyote numbers. In the last five
years coyote populations have decreased somewhere between 30-50%.
For the first four years wolves would simply kill coyotes and leave
the carcass, but in 1999 researchers observed the Druid peak pack
kill a number of coyote pups and bring them back to the den to feed
their own pups.
This all has affected coyote behavior in many ways.
It is now observed that coyotes den very close to human settlements
within the park, so as to stay away from the core wolf territories.
Another interesting response that has been observed within the last
year is a fundamental breakdown of the pack structure they once
showed five years ago. There have been multiple litters within loose
packs (no alpha male and female) and the "helpers" within the pack
no longer help, but are observed to be hunting and foraging more
on their own. These could all be mechanisms to combat increased
mortality or it could be because food supply has increased with
the number of carcasses left by wolves. Either way studies are currently
being done to get a better understanding of the coyotes place now
within the GYE.
Not a lot of information is currently known about
black bear/ wolf interactions. Most observations have been of
wolves chasing black bears off of kill sites. But when dealing
with large predators this can also be a numbers game. A solitary
bear can displace a solitary wolf off of a kill site.
Ther has not been a documented case of wolves
killing a mature grizzly as well as vice versa. But there have
been multiple observations of grizzlies displacing wolves from
kill sites as well as approaches to wolf den sites.
The biggest influence on cougars is determined
by a significant dietary and spatial overlap. This is determined
three ways. First, alter population characteristics such as
age ratios. Second is animal behavior and third is the distribution
of prey. There have been no observable interactions of wolves
and cougars but research continues.
Elk currently constitute roughly 85% of the GYE
wolves diet. The 12+ packs that exist within the GYE take an
approximated 130 elk per year. This has not affected elk populations
significantly, the biggest affect has been the recruitment of
younger elk, but otherwise the elk population has seen an overall
decrease of 8-20% relative to the year populations are counted
and accounting for winter and summer ranges.
There are no direct predation numbers known of
bison but researchers do know that wolves have been "learning"
to kill bison and have been successfully hunting them since
the winter of 1997, when they took two bison.
During the winter of 1997 moose consisted of 11%
of the GYE wolves diet. Researchers believed this was a higher
amount of predation than to be expected on a regular basis.
Moose will most likely make up 5-11% of the annual diet of the
GYE wolves. There should be no population affect.
Yellowstone Bighorn sheep
As to date there has been no predation of bighorn
sheep by wolves. It is even possible that bighorn sheep populations
might be increasing due to the fact that they are able to occupy
areas once overrun by elk.
Yellowstone Pronghorn Antelope
The pronghorn is expected to see the same effect
as that of the bighorn. A relative increase in population due
to the fact that they are fairly unavailable to wolves and would
therefore occupy territories once occupied by large numbers
Yellowstone White-tail deer/Mountain goats
These two species are generally regarded as a
scavenging option for wolves in the GYE and probably will not
be affected (as they haven’t been so far) by the reintroduction.
This is due to their low numbers and the geographical niches
Between the years of 1995-1999 wolves within
the GYE had taken thirteen cattle.
These numbers are fairly inconsistent but the
last accurate count in 1998 was fifty-five sheep lost to wolves
within the GYE.
Domestic dogs are likely killed because of territory
disputes. The dog will defend his or her "master’s" territory
much the same a pack will defend their territory. There have
been six confirmed losses to wolves over the past five years.
Suspected other prey species (known or suspected
in Greater Yellowstone Ecosystem)
-Northern pocket gopher
-Uinta ground squirrel
-Golden-mantled ground squirrel
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Yellowstone trophic effects
Figure 8.9; Carnivores in Ecosystems: Ungulates In Yellowstone,
Singer and Mack 1999.
Yellowstone pack morphology
Currently there are 118+ wolves located within the Greater Yellowstone
Ecosystem. They are formed into an approximate 12+ packs that are
very fluid in structure.
For a complete and updated synopsis of pack morphology, pup counts,
mortality counts, and dispersing individuals numbers click
For updated observations and pack movements click