History of wolves in Yellowstone - AbsoluteAstronomy.com

Yellowstone National Park

Yellowstone National Park, established by the U.S. Congress and signed into law by President Ulysses S. Grant on March 1, 1872, is a national park located primarily in the U.S. state of Wyoming, although it also extends into Montana and Idaho...

was created in 1872, gray wolf

Gray Wolf

The gray wolf , also known as the wolf, is the largest extant wild member of the Canidae family...

(Canis lupus) populations were already in decline in Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

, Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

and Idaho

Idaho

Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

. The creation of the national park did not provide protection for wolves or other predators, and government predator control programs in the first decades of the 1900s essentially helped eliminate the gray wolf from Yellowstone. The last wolves were killed in Yellowstone in 1926. After that time, sporadic reports of wolves still occurred, but scientists confirmed that sustainable wolf populations had been extirpated and were absent from Yellowstone during the mid 1900s.

Starting in the 1940s, park managers, biologists, conservationists and environmentalists began what would ultimately turn into a campaign to reintroduce the gray wolf into Yellowstone National Park. When the Endangered Species Act of 1973 was passed, the road to legal reintroduction was clear. In 1995, gray wolves were first reintroduced into Yellowstone in the Lamar Valley

Lamar River

The Lamar River is a tributary of the Yellowstone River, approximately 40 miles long, in northwestern Wyoming in the United States. The river is located entirely within Yellowstone National Park.-History:...

. The history of wolves in Yellowstone chronicles the extirpation, absence and reintroduction of gray wolves to Yellowstone, and how the reintroduction was not without controversy or surprises for scientists, governments or park managers.

Extirpation (1872–1926)

In 1872, when Yellowstone National Park

Yellowstone National Park

was created, there was yet no legal protection for wildlife in the park. In the early years of the park, administrators, poachers and tourists were essentially free to kill any game or predator they came across. The Gray Wolf was especially vulnerable to this wanton killing because it was generally considered an undesirable predator and was being willingly extirpated throughout its North American range. In January 1883, the Secretary of the Interior issued regulations prohibiting hunting of most park animals, but the regulations did not apply to Wolves, Coyotes, Bears, Mountain Lions and other small predators.

Shortly after the U.S. Army took over administration of the park on August 20, 1886, Captain Moses Harris, the first military superintendent, banned public hunting of any wildlife and any predator control was to be left to the park's administration. Official records show however, that the U.S. Army did not begin killing any wolves until 1914.

In 1885, Congress created the Division of Economic Ornithology and Mammalogy with the express purpose of research for the protection of wildlife. The agency soon became the U.S. Biological Survey which was the forerunner of the U.S. Fish and Wildlife Service. In 1907, under political pressure from the western cattle and livestock industries, this agency began a concerted program which eventually was called: Animal Damage Control. This predator control program alone killed 1800 wolves and 23,000 coyotes in 39 U.S. National Forests in 1907. In 1916, when the National Park Service was created, its enabling legislation included words that authorized the Secretary of the Interior to "provide in his discretion for the destruction of such animals and of such plant life as may be detrimental to the use of said parks, monuments and reservations".

It is generally accepted that sustainable Gray Wolf packs had been extirpated

Local extinction

Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...

from Yellowstone National Park by 1926, although the National Park Service maintained its policies of predator control in the park until 1933. However, a 1975–77 National Park Service sponsored study revealed that during the period 1927 to 1977, there were several hundred probable sightings of wolves in the park. Between 1977 and the re-introduction in 1995, there were additional reliable sightings of wolves in the park, most believed to be singles or pairs transiting the region.

Official records of wolves killed

Prior to the National Park Service assuming control of the park in 1916, the U.S. Army killed 14 wolves during their tenure (1886–1916), most in the years 1914–15. In 1940, Adolph Murie

Adolph Murie

Adolph Murie , the first scientist to study wolves in their natural habitat, was a naturalist, author, and wildlife biologist who pioneered field research on wolves, bears, and other mammals and birds in Arctic and sub-Arctic Alaska...

, a noted wildlife biologist published his Fauna Series No. 4—Fauna of the National Parks of the United States-Ecology of the Coyote in the Yellowstone National Park. In this report, Murie tallied the number of wolves killed as reported annually by park administrators between 1915 and 1935:

From the Superintendent's Annual Report for:
Year	Number killed
1915	Several
1916	14
1917	4
1918	36
1919	6
1920	28
1921	12
1922	24
1923	8
1924–1935	0

Updated research in the 1980s verified that the last official killing of wolves in the park took place in 1926 when two pups found near Soda Butte Creek

Soda Butte Creek

Soda Butte Creek is an approximately long major tributary of the Lamar River in Yellowstone National Park. It is named for an unusual geologic feature near its mouth. Soda Butte and the creek were named by A. Bart Henderson, a Cooke City miner, in 1870...

were killed by park rangers. The last reported wolf killed in the Greater Yellowstone Ecosystem (prior to today’s legal hunting or control measures) occurred in May 1943 when Leo Cottenoir, a Native American

Native Americans in the United States

Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...

sheepheader on the Wind River Reservation shot a wolf near the southern border of the park.

Ecological impacts

Once the wolves were gone the elk began to take over. Over the next few years conditions of Yellowstone National Park declined drastically. A team of scientists visiting Yellowstone in 1929 and 1933 reported, “The range was in deplorable conditions when we first saw it, and its deterioration has been progressing steadily since then.” By this time many biologists were worried about eroding land and plants dying off. The elk were multiplying inside the park and deciduous, woody species such as aspen and cottonwood suffered from overgrazing. The park service started trapping and moving the elk and, when that was not effective, killing them. This killing continued for more than 30 years. This method helped the land quality from worsening, but didn't improve the conditions. At times, people would mention bringing wolves back to Yellowstone to help control the elk population. The Yellowstone managers were not eager to bring back wolves, especially after having so successfully ridding the park of them, so they continued killing elk. In the late 1960s, local hunters began to complain to their congressmen that there were too few elk, and the congressmen threatened to stop funding Yellowstone. Killing elk was given up as a response, and then the population of the elk increased exponentially. With the rapid increase in the number of elk, the condition of the land again went quickly downhill. The destruction of the landscape affected many other animals. With the wolves gone, the population of coyotes increased dramatically, which led to an extreme decrease in the number of pronghorn antelope. However, the increase in the elk population caused the most profound change in the ecosystem of Yellowstone after the wolves were gone.

Re-introduction initiatives

The campaign to restore the Gray Wolf in Yellowstone had its roots in a number of seminal studies related to the predator-prey ecology of the park. In 1940 Adolph Murie published Ecology of the Coyote in the Yellowstone National Park. That study and his 1940–41 work The Wolves of Mount McKinley was instrumental in building a scientific foundation for wolf conservation. In 1944, noted wildlife biologist Aldo Leopold

A. Starker Leopold

Aldo Starker Leopold was an American author, forester, zoologist and conservationist. He also served as professor at the University of California, Berkeley for thirty years...

, once an avid predator control advocate, made the following comments in his review of The Wolves of North America, Young and Goldman, 1944:
By the 1960s, cultural and scientific understanding of ecosystems was changing attitudes toward the wolf and other large predators. In the early 1960s, Douglas Pimlott, a noted Canadian wildlife biologist was calling for the restorations of wolves in the northern rockies. In 1970 American wolf expert, David Mech published The Wolf: The Ecology and Behavior of an Endangered Species (1970, 1981), an enlightening study of the wolf and its impact on its environment. In 1978, when wildlife biologist John Weaver published his seminal study Wolves of Yellowstone, he concluded the report with the following recommendation:
The Gray Wolf was one of the first species to be listed as endangered (1967) under the Endangered Species Preservation Act of 1966

Endangered Species Preservation Act of 1966

In the United States the Endangered Species Preservation Act of 1966 was the predecessor to the Endangered Species Act.Passed by Congress, this act permitted the listing of native U.S animal species as endangered and for limited protections upon those animals.This Act caused the Secretary of the...

. However, until the passage of the Endangered Species Act of 1973, there was no legal basis or process for re-introducing the Gray Wolf to Yellowstone National Park and the Greater Yellowstone Ecosystem. The Endangered Species Act obligated the U.S. Fish and Wildlife Service to develop restoration plans for each species designated as Endangered. The first recovery plan was completed in 1980 but gained little traction. In 1987, the U.S. Fish and Wildlife Service published a revised Northern Rocky Mountain Wolf Recovery Plan. that led the way to wolf reintroduction. The plan was a cooperative effort between the National Park Service, Fish and Wildlife Service, academia, state wildlife agencies and environmental groups. Its Executive Summary contains the following:
In 1991 Congress directed the U.S. Fish and Wildlife Service to develop an Environmental Impact Statement

Environmental impact statement

An environmental impact statement , under United States environmental law, is a document required by the National Environmental Policy Act for certain actions "significantly affecting the quality of the human environment". An EIS is a tool for decision making...

(EIS) for the express purpose of reintroducing wolves into Yellowstone National Park and regions of Central Idaho. The final statement was published on April 14, 1994 and seriously examined five potential alternatives for reestablishing wolves in Yellowstone and central Idaho.

Reintroduction of Experimental Populations (incorporating most of the state implemented nonessential reintroduction alternative with parts of the 1987 Recovery Plan).
Natural Recovery (with limited land-use restrictions in anticipation of some illegal killing of wolves).
No Wolf (as proposed in alternative scoping).
Wolf Management Committee (as proposed by Congress).
Reintroduction of Non-experimental Wolves (incorporating the accelerated wolf recovery alternative but with fewer land-use restrictions)

Alternative 1 was the recommended and ultimately adopted alternative:
The final EIS opened the way for re-introduction, but not without opposition. The Sierra Club

Sierra Club

The Sierra Club is the oldest, largest, and most influential grassroots environmental organization in the United States. It was founded on May 28, 1892, in San Francisco, California, by the conservationist and preservationist John Muir, who became its first president...

and National Audubon Society

National Audubon Society

The National Audubon Society is an American non-profit environmental organization dedicated to conservation. Incorporated in 1905, Audubon is one of the oldest of such organizations in the world and uses science, education and grassroots advocacy to advance its conservation mission...

opposed the re-introduction plan on the grounds that Experimental populations were not protected enough once the wolves were outside the park. The Farm Bureau's of Idaho, Wyoming and Montana opposed the plan on the basis that the wrong subspecies of wolf—Canis lupus occidentalis (Mackenzie Valley Wolf

Mackenzie Valley Wolf

The Mackenzie Valley Wolf also known as the Canadian Timber Wolf is perhaps the largest subspecies of Gray Wolf in North America. Its range includes parts of the western United States, much of western Canada, and Alaska, including Unimak Island in the Aleutians, and was introduced into Yellowstone...

(Canada)) instead of Canis lupus irremotus (Northern Rocky Mountain Gray Wolf

Northern Rocky Mountains Wolf

The Northern Rocky Mountains Wolf , also known as the Northern Rocky Mountain Wolf, is a subspecies of the gray wolf, Canis lupus, that is primarily found in the northern portion of the Rocky Mountains and the states and provinces surrounding the region...

) was selected for reintroduction. These objections were overcome and in January 1995, the process of physically reintroducing wolves into Yellowstone began.

Initial releases 1995–96

In January 1995, U.S. and Canadian wildlife officials captured 14 wolves from multiple packs east of Jasper National Park, near Hinton, Alberta, Canada. These wolves arrived in Yellowstone in two shipments—January 12, 1995 (8 wolves) and January 20, 1995 (6 wolves). They were released into three acclimation pens—Crystal Creek, Rose Creek and Soda Butte Creek

Soda Butte Creek

in the Lamar Valley in Northeast East Yellowstone National Park. In March 1995, the pens were opened and between March 21 and March 31, 1995 all 14 wolves were loose in Yellowstone.

Seventeen (17) additional wolves captured in Canada arrived in Yellowstone in January 1996 and were released into the park in April 1996 from the Chief Joseph, Lone Star, Druid Peak and Nez Perce pens. These were last wolves released into to park as officials believed that the natural reproduction and survival were sufficient to preclude additional releases.

Annual wolf status since reintroduction

Wolf population declines, when they occur, result from "intraspecific

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

strife," food stress, mange

Mange

Mange is the common name for a class of persistent contagious skin diseases caused by parasitic mites. Since mites also infect plants, birds, and reptiles, the term "mange," suggesting poor condition of the hairy coat due to the infection, is sometimes reserved only for pathological...

, canine distemper

Canine distemper

Canine distemper is a viral disease that affects animals in the families Canidae, Mustelidae, Mephitidae, Hyaenidae, Ailuridae, Procyonidae, Pinnipedia, some Viverridae and Felidae...

, legal hunting of wolves in areas outside the park (for sport or for livestock protection) and in one case in 2009, lethal removal by park officials of a human-habituated wolf.

*1995-99 Data reflects status of the wolf in the Greater Yellowstone Ecosystem
Greater Yellowstone Ecosystem
The Greater Yellowstone Ecosystem is one of the last remaining large, nearly intact ecosystems in the northern temperate zone of the Earth and is partly located in Yellowstone National Park. Conflict over management has been controversial, and the area is a flagship site among conservation groups...

. Since 2000 monitoring has focused on packs operating within park boundaries. Wolves continue to spread to surrounding areas, and the last official report by the park for the Greater Yellowstone Area counted 272 wolves in 2002.

Annual Status of Wolves in Yellowstone (As of December)
Year	Total Number of Packs	Total Number of Wolves	3	21	9
1996*	9	51	14
1997*	9	86	49
1998*	11	112	36
1999*	11	118	38
2000	8	119	55-60
2001	10	132	43
2002	14	148	58
2003	13–14	174	59
2004	16	171	59
2005	13	118	22
2006	13	136	60
2007	11	171	64
2008	12	124	22
2009	14	96	23
2010	11	97	38

Ecological impacts after re-introduction

Scientists have been researching and studying the impacts on the Yellowstone ecosystem since re-introduction in 1995.

As the wolf population in the park has grown, the elk population, their favored prey, has declined. Prior to reintroduction, the EIS predicted that wolves would kill an average 12/wolf elk annually. This estimate proved too low as wolves are now killing an average of 22/wolf annually. This decline in elk has resulted in changes in flora, most specifically willows, cottonwoods and aspens along the fringes of heavily timbered areas. Although wolf kills are directly attributable to declines in elk numbers, some research has shown that elk behavior has been significantly altered by wolf predation. The constant presence of wolves have pushed elk into less favorable habitats, raised their stress level, lowered their nutrition and their overall birth rate.

The wolves became significant predators of coyotes after their reintroduction. Since then, in 1995 and 1996, the local coyote population went through a dramatic restructuring. Until the wolves returned, Yellowstone National Park had one of the densest and most stable coyote populations in America due to a lack of human impacts. Two years after the wolf reintroductions, the pre-wolf population of coyotes had been reduced to 50% through both competitive exclusion and intraguild predation

Intraguild predation

Intraguild predation, or IGP, is the killing and eating of potential competitors. This interaction represents a combination of predation and competition, because both species utilize the same prey resources and also benefit from preying upon one another...

. Coyote numbers were 39% lower in the areas of Yellowstone where wolves were reintroduced. In one study, about 16% of radio-collared coyotes were preyed upon by wolves. Yellowstone coyotes have had to shift their territories as a result, moving from open meadows to steep terrain. Carcasses in the open no longer attract coyotes; when a coyote is chased on flat terrain, it is often killed. They feel more secure on steep terrain where they will often lead a pursuing wolf downhill. As the wolf comes after it, the coyote will turn around and run uphill. Wolves, being heavier, cannot stop and the coyote gains a large lead. Though physical confrontations between the two species are usually dominated by the larger wolves, coyotes have been known to attack wolves if they outnumber them. Both species will kill each other's pups given the opportunity.

Coyotes, in their turn, naturally suppress foxes, so the diminished coyote population has led to a rise in foxes, and "That in turn shifts the odds of survival for coyote prey such as hare

Hare

Hares and jackrabbits are leporids belonging to the genus Lepus. Hares less than one year old are called leverets. Four species commonly known as types of hare are classified outside of Lepus: the hispid hare , and three species known as red rock hares .Hares are very fast-moving...

s and young deer, as well as for the small rodent

Rodent

Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....

s and ground-nesting birds the foxes stalk. These changes affect how often certain roots, buds, seeds and insects get eaten, which can alter the balance of local plant communities, and so on down the food chain all the way to fungi and microbes."

The presence of wolves has also coincided with a dramatic rise in the park's beaver

Beaver

The beaver is a primarily nocturnal, large, semi-aquatic rodent. Castor includes two extant species, North American Beaver and Eurasian Beaver . Beavers are known for building dams, canals, and lodges . They are the second-largest rodent in the world...

population; where there was just one beaver colony in Yellowstone in 2001, there were nine beaver colonies in the park by 2011. The presence of wolves seems to have encouraged elk to browse more widely, diminishing their pressure on stands of willow

Willow

Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...

, a plant that beavers need to survive the winter. The renewed presence of beavers in the ecosystem has substantial effects on the local watershed because the existence of beaver dams "even[s] out the seasonal pulses of runoff; store[s] water for recharging the water table; and provide[s] cold, shaded water for fish." Beaver dams also counter erosion and create "new pond and marsh habitats for moose

Moose

The moose or Eurasian elk is the largest extant species in the deer family. Moose are distinguished by the palmate antlers of the males; other members of the family have antlers with a dendritic configuration...

, otter

Otter

The Otters are twelve species of semi-aquatic mammals which feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals....

s, mink

Mink

There are two living species referred to as "mink": the European Mink and the American Mink. The extinct Sea Mink is related to the American Mink, but was much larger. All three species are dark-colored, semi-aquatic, carnivorous mammals of the family Mustelidae, which also includes the weasels and...

, wading birds, waterfowl, fish, amphibians and more."

Wolf kills are scavenged

Scavenger

Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...

by and thus feed a wide array of animals, including, by not limited to, raven

Raven

Raven is the common name given to several larger-bodied members of the genus Corvus—but in Europe and North America the Common Raven is normally implied...

s, wolverine

Wolverine

The wolverine, pronounced , Gulo gulo , also referred to as glutton, carcajou, skunk bear, or quickhatch, is the largest land-dwelling species of the family Mustelidae . It is a stocky and muscular carnivore, more closely resembling a small bear than other mustelids...

s, bald eagle

Bald Eagle

The Bald Eagle is a bird of prey found in North America. It is the national bird and symbol of the United States of America. This sea eagle has two known sub-species and forms a species pair with the White-tailed Eagle...

s, golden eagle

Golden Eagle

The Golden Eagle is one of the best known birds of prey in the Northern Hemisphere. Like all eagles, it belongs to the family Accipitridae. Once widespread across the Holarctic, it has disappeared from many of the more heavily populated areas...

s, grizzly bear

Grizzly Bear

The grizzly bear , also known as the silvertip bear, the grizzly, or the North American brown bear, is a subspecies of brown bear that generally lives in the uplands of western North America...

s, black bears, jay

Jay

The jays are several species of medium-sized, usually colorful and noisy, passerine birds in the crow family Corvidae. The names jay and magpie are somewhat interchangeable, and the evolutionary relationships are rather complex...

s, magpie

Magpie

Magpies are passerine birds of the crow family, Corvidae.In Europe, "magpie" is often used by English speakers as a synonym for the European Magpie, as there are no other magpies in Europe outside Iberia...

s, marten

Marten

The martens constitute the genus Martes within the subfamily Mustelinae, in family Mustelidae.-Description:Martens are slender, agile animals, adapted to living in taigas, and are found in coniferous and northern deciduous forests across the northern hemisphere. They have bushy tails, and large...

s and none-too-bright coyotes cruisin' for a bruisin'.

Meanwhile, wolf packs often claim kills made by mountain lions, which has driven the cougar

Puma

The cougar , also known as puma, mountain lion, mountain cat, catamount or panther, depending on the region, is a mammal of the family Felidae, native to the Americas...

s back out of valley hunting grounds to their more traditional mountainside territory.

The top-down effect of the reintroduction of an apex predator

Apex predator

Apex predators are predators that have no predators of their own, residing at the top of their food chain. Zoologists define predation as the killing and consumption of another organism...

like the wolf on other flora and fauna in an ecosystem is an example of a trophic cascade

Trophic cascade

Trophic cascades occur when predators in a food web suppress the abundance of their prey, thereby releasing the next lower trophic level from predation...

2009 removal from Endangered Species List

Because Gray Wolf populations in Montana, Wyoming and Idaho had recovered sufficiently to meet the goals of the Wolf Recovery Plan, on May 4, 2008 the U.S. Fish and Wildlife Service changed the status of the gray wolf population known as the Northern Rocky Mountains Distinct Population Segment from Endangered to Experimental Population-Non Essential.

The wolves in Yellowstone and the Greater Yellowstone Ecosystem fall within this population. In response to the change in status, state wildlife authorities in Idaho and Montana enacted quota-based hunting seasons on wolves as part of their approved state Wolf Management Plans. Environmental groups objected to the delisting and the hunting seasons, but despite legal attempts to stop them (Defenders of Wildlife
Defenders of Wildlife
Defenders of Wildlife is a United States-based, 501 non-profit organization founded in 1947, "dedicated to the protection of all native animals and plants in their natural communities." The organization is active in political interventions and lobbying aimed at protection of wildlife, and...

et al v Ken Salazar
Ken Salazar
Kenneth Lee "Ken" Salazar is the current United States Secretary of the Interior, in the administration of President Barack Obama. A member of the Democratic Party, he previously served as a United States Senator from Colorado from 2005 to 2009. He and Mel Martinez were the first Hispanic U.S...

et al), the wolf hunts, which commenced in Montana in September 2009 were allowed to proceed. A number of noted wildlife biologists that had been instrumental in the restoration of wolves—David Mech, Douglas Smith, and Mark Hebblewhite supported the state wildlife management plans and the delisting because they believed the wolf populations were now at sustainable levels.

Although wolves within the park boundaries were still fully protected, wolves that ventured outside the boundaries of the park into Idaho or Montana could now be legally hunted. During these hunts, Montana hunters legally killed a number of wolves in the Absaroka-Beartooth Wilderness

Absaroka-Beartooth Wilderness

Absaroka-Beartooth Wilderness was created from existing National Forest lands in 1975 and is located in Montana and Wyoming, United States. The wilderness is partly in Gallatin, Custer and Shoshone National Forests and is composed of . The wilderness encompasses two distinct mountain ranges, namely...

known to frequent the northeast corner of the park.

Hunting opportunities

During 2000–2004, the Montana Fish, Wildlife and Parks reduced antlerless permits by 51% from 2,882 to 1,400. More recently, it proposed only 100 permits for 2006 which is a 96% decrease from the 2,660 permits issued in 1995. Initially, the effects of wolf predation on elk during the first five years of the recovery were not detected, as elk numbers were identical to those of 1980–1994. From the winter of 1995 to the winter of 2004 however, the elk greatly decreased in number, dropping from 16,791 to 8,335 as the number of wolves on the northern range increased from 21 to 106, though predation from bears, increased human harvests, winter and droughts were also factors. Since 2000, 45% of known deaths and 75% of predation-caused deaths of radio collared cow-elk have been confirmed to be attributable to wolves. Human caused deaths in the same period accounted for 8–30% of known deaths. Yellowstone elk comprise up to 92% of the winter diet of wolves, the overall kill rates of Yellowstone wolves on elk in winter being estimated at 22 ungulates per wolf annually. This is higher than the 12 ungulates per wolf rate predicted in the ESA.

Subspecies

Historically, the wolf populations originally native to Yellowstone were classed under the subspecies C. l. irremotus. When the issue of what subspecies to use for the introduction was raised, park service representatives stated that the taxonomy of grey wolves had been revised numerous times, and that C. l. irremotus was not a distinct subspecies, but a geographical variant. Three publications were made on the appropriateness of using a founding population of Canadian wolves: Brewster and Fritz supported the motion, while Nowak determined that the original Yellowstone wolves were more similar to C. l. nubilus, a subspecies already present in Minnesota, and that the Canadian animals proposed by Brewster and Fritz were of the subspecies C. l. occidentalis, a significantly larger animal. The rationale behind Brewster and Fritz's favour was that wolves show little genetic diversity, and that the original population was extinct anyway. This was contradicted by Nowak, who contested that Minnesotan wolves were much more similar in size and shape to the original population than the proposed Canadian wolves, though he conceded that C. l. occidentalis was probably already migrating southward even before human intervention. The final use of Canadian wolves for the reintroduction was not without criticism: the American Society of Mammalogists criticised the project's lack of deference to the principle of Bergmann's rule

Bergmann's Rule

Bergmann's rule is an ecogeographic principle that states that within a broadly distributed genus, species of larger size are found in colder environments, and species of smaller size are found in warmer regions. Although originally formulated in terms of species within a genus, it has often been...

, pointing out that the wolves used for the introduction were 30% larger than the original park wolves, and were adapted to much colder climates. Finally, the society questioned the legality under the ESA of “recovering” a taxon of wolf by expanding the historic range of a less similar type, when more closely related founder stock still remained available.