Reintroduction of the Gray Wolf to the Greater Yellowstone Ecosystem (GYE)
Gray wolves (Canis lupus) once roamed the western portions of North America from Alaska to
Mexico. During the latter part of the nineteenth century, most of the important prey for wolves
— bison, deer, elk, and moose — were severely depleted by human settlers. The wolves soon
became the enemies of the ranchers and farmers when they turned to preying upon sheep and
other livestock. When the federal government set aside the Greater Yellowstone Ecosystem
(GYE) as a national park in 1872, about three to four hundred wolves were present, preying
mostly upon large hooved ungulates such as elk (Cervus canadensis) and bison (Yellowstone
Association 1996). Fearing the wolves' impact on elk and bison herds as well as livestock owned
by area ranchers, the federal government began eradicating the wolf population. Bounty
programs that continued until 1965 offered as much as $50 per wolf. Wolves were trapped,
shot, dug from their dens, hunted with dogs, and poisoned. In Yellowstone National Park, park
rangers killed the last two remaining pups in 1924. By the 1930s wolves had been effectively
eliminated from the contiguous 48 States and Mexico and only remained in high numbers in
Alaska.
With their primary predator eliminated, elk populations exploded, leading to the overgrazing of
plants, especially those found in riparian zones (Laliberte & Ripple 2004). Significant declines in
the populations of many plant species (e.g., aspen, willow) resulted, which in turn influenced
other wildlife, such as beaver and songbird populations (Ripple & Breschetta 2004, Hallofsky &
Ripple 2008). Intensive browsing of aspen (Populus tremuloides) stands, for example, led to a
rapid decline in the number of seedlings and root sprouts growing into saplings and trees. For
many stands of these trees, only large diameter trees (i.e., those that had matured before the
wolves were eradicated) remained.
Disappearance of these and other plant species not only caused the loss of habitat for many
other animals but also influenced other ecological factors (Smith et al. 2009), including stream
bank stability, the deposition of organic matter and fine sediment in riparian zones, water
temperature regulation via shading, and nutrient cycling. The removal of wolves thus led to the
instability of riparian and other environmentally sensitive areas.
After the United States Congress passed the original Endangered Species Preservation Act in
1966, the gray wolf made the original Endangered Species List. The subsequent Endangered
Species Act of 1973 called for their restoration. Consequently, the National Park Service
changed their policy to restore natural conditions within Yellowstone National Park, including
the reintroduction of the gray wolf (Smith & Bangs 2009).
At the time of reintroduction, the following factors were taken into account in the decision to
undertake the reintroduction of the gray wolves:
1. Yellowstone National Park (YNP) is the United States flagship park and, as such, deserves
special consideration. Gray wolves constituted the only native vertebrate species that
was not represented in the park before the reintroduction began.
2. The loss of gray wolves from the park (and the surrounding area) was caused by
widespread elimination by humans that perceived the wolves as a threat to livestock
and family. A serious eradication effort occurred primarily from 1900 to the 1930s. The
last wolf in YNP was killed in 1926.
3. Gray wolves are a keystone predator (play a major role in keeping a natural balance
between species).
4. Since the removal of gray wolves from the area, the number of elk has increased
dramatically to the point that they are adversely affecting other species in the park (i.e.
eating so many young lodgepole pine trees and other saplings that the forests are not
being replaced).
At the time of reintroduction, reasons given for opposing the wolf relocation project included
the following:
1. Some people do not like, or trust, wolves.
2. This money could/should be spent on human problems such as hunger, etc.
3. Some of the people in the area were alive when the government was encouraging the
removal of the wolves. The change in policy does not make sense to these people.
4. In 1996 wolves released in YNP are known to have killed 12 sheep and one dog. The
wolves responsible were captured and moved (when possible). One wolf returned to the
area in which it had killed sheep and was killed by federal agents.
5. Some ranchers believe that the losses will be much greater than estimated, and will
drive them out of business.
In 1995, the federal government began reintroducing gray wolves into the GYE. Initially,
fourteen wolves were captured in Canada and relocated to one-acre acclimation pens where
they were held for ten weeks before being released into the GYE. This process was repeated in
1996 and 1997 with an additional seventeen wolves from Canada and ten pups from Montana
(Smith et al. 2009). The cost of the reintroduction of gray wolves to Yellowstone National Park
(YNP) in 1996 was $267,000. For the most part, wolf populations have continued to grow at a
rapid rate, averaging 17% per year (Smith & Bangs 2009). At the end of 2009, there were
between 96 and 98 wolves in Yellowstone, with 14 packs, 1 non-pack grouping, and 2 loners
(Figure 6). Park staff recorded 365 prey animals killed by wolves, most of which were elk (302).
Despite some setbacks (e.g., disease outbreaks within the fledgling wolf packs), recovery efforts
in the GYE have greatly surpassed expectations. Since their reintroduction, wolves have
overwhelmingly targeted elk over other prey. This has coincided with an increase in willow
heights in several areas. This may indicate that a wolf-elk-willow trophic cascade has been
reestablished within the GYE. Furthermore, investigators believe that restoration of willow
populations has led to a ten-fold increase in beaver populations (Smith 2004) as well as a
significant songbird rebound (Baril & Hansen 2007).
Halofsky & Ripple (2008) found that aspen browsing by elk had ceased in areas burned during
the historic 1988 fires but continued in unburned areas. These results were attributed to the
increased risk of wolf predation in burned areas. The authors proposed that a recoupling of fire
with increased predation risk from wolves may help improve aspen restoration. The results also
suggest that much more research needs to be conducted to determine the effects of wolf
reintroduction into the GYE.
Other factors to consider include:
Gray wolves that have been reintroduced to Yellowstone National Park were specifically chosen
from wild populations living in mountainous areas where elk and deer were the primary prey,
and livestock and potentially infectious diseases were rare. Wolves from Alberta and British
Columbia, Canada met these conditions. Note: gray wolves are not endangered in Canada - they
are locally endangered in the contiguous 48 states where they used to thrive, but are not
globally endangered.
Wolves have been observed to colonize new areas and to adapt well if proper habitat is
available. Wolves are recolonizing their former range in the Northern Rockies, but are not
expected to reach YNP naturally for at least 60 years.
A keystone species is a species that has a disproportionately large effect on its environment
relative to its abundance. Gray wolves are considered a keystone species with the ability to
initiate a trophic cascade. A trophic cascade occurs when a predator in a food web suppresses
the abundance of a prey species, which in turn allows the next lower trophic level to thrive. A
report from Oregon State University plant researchers William J. Ripple and Bob Beschta
reinforces the belief that the wolf has been the primary factor in the improved health of aspen,
willow, and cottonwood trees in Yellowstone National Park's Northern Range. This in turn has
benefitted such Yellowstone wildlife as beaver, bison, pronghorn, songbirds, raptors, and trout.
The return of the wolf has changed elk behavior and reduced some herds, but overall numbers
remain strong in Idaho, Montana and Wyoming. According to Yellowstone biologist Doug Smith,
the Yellowstone herds remain healthy despite its smaller size. The number is more in line with
historic levels since wolves were reintroduced and grizzly bears and mountain lions returned
naturally. Overall elk populations in the states of Idaho, Montana, and Wyoming remain healthy
with an estimated 103,000 in Idaho, 150,000 in Montana, and 120,000 in Wyoming. However,
elk populations are now more dynamic with the return of large carnivores and elk distribution
has shifted to areas that are more difficult to hunt.
A non-governmental organization (NGO), "Defenders of Wildlife", has agreed to compensate
ranchers for documented livestock loss (but not pet loss) due to wolf kills. The goal is to shift
economic responsibility for wolf recovery away from the individual rancher and toward the
millions of people who want to see wolf populations restored. When ranchers alone are forced
to bear the cost of wolf recovery, it creates animosity and ill will toward the wolf. Such negative
attitudes can result in illegal killing. Some ranchers say they would not submit a claim on the
grounds of not "buying in" to the reintroduction.
SUMMARY OF PAYMENTS BY YEAR (thru 2008)
2008 $226,891 131 Payments 195 Cattle, 238 Sheep, 22 Other
2007 $239,862 152 Payments 235 Cattle, 309 Sheep, 6 Other
2006 $181,765 101 Payments 195 Cattle, 205 Sheep, 8 Other
2005 $101,086 75 payments 102 Cattle, 83 Sheep, 6 Other
2004 $138,091 94 Payments 108 Cattle, 452 Sheep, 9 Other
2003 $63,145 53 Payments 52 Cattle, 210 Sheep, 14 Other
2002 $64,174 46 Payments 75 Cattle, 133 Sheep, 8 Other
2001 $53,297 34 Payments 67 Cattle, 149 Sheep, 2 Other
2000 $50,446 38 Payments 36 Cattle, 105 Sheep,13 Other
1999 $35,937 40 Payments 51 Cattle, 108 Sheep, 6 Other
1998 $17,483 17 Payments 27 Cattle, 13 Sheep, 5 Other
1997 $26,065 21 Payments 24 Cattle, 152 Sheep
1996 $7,483 9 Payments 8 Cattle, 49 Sheep
1995 $1,633 2 Payments 4 Cattle
Name________________________________________ Period_____ Date______________
Questions:
1. Describe the history of the Gray Wolf in the western United States. When and why did it
face extinction? When did reintroduction begin? Describe the current population size(s)
and status.
2. In your view, should the priority in National Parks be their role as recreational areas or
as refuges for wildlife? Why or why not?
3. What responsibilities do National Parks have to their neighbors?
4. Suppose you are a wildlife biologist and you were told that the introduction of the Gray
Wolves has been so successful that it was responsible for roughly a 50% reduction in the
size of the elk herd over the last 15 years, more than double the projected 20% decline
projected by wildlife biologists before the reintroduction. This has caused elk guides
(those who take hunters on hunting trips) to lose income and in some cases lose their
jobs altogether. Elk hunting license fees pay for much of the wildlife research in the
Greater Yellowstone Ecosystem and elk are a vital part of the ecosystem themselves. Do
you recommend that gray wolves be hunted to keep their population in balance? Why
or why not?
5. Would your opinion about the management of the gray wolf change if the U.S. Fish and
Wildlife service predicted that a human death could be expected as a result of not
hunting them? Why, or why not?
6. Suppose you were a wildlife biologist charged with designing a wolf management plan
for the Greater Yellowstone Ecosystem, which includes millions of acres comprising the
national park, other adjacent public lands, and private lands (ranches, housing
developments, forest, etc.). What would your management plan be?
7. Describe the meaning of the term keystone species and summarize the evidence in the
Yellowstone region that supports the idea that wolves fit this definition. What other
species in the GYE might be considered a keystone species?
8. What is a trophic cascade? How did the presence of wolves in the GYE initiate a trophic
cascade?