The gray wolf or grey wolf, also known as the timber wolf or western wolf, is a canine native to the wilderness
and remote areas of Eurasia and North America. It is the largest extant member of its family, with males
averaging 43-45 kg (95-99 lb), and females 36-38.5 kg (79-85 lb). Like the red wolf, it is distinguished
from other Canis species by its larger size and less pointed features, particularly on the ears and muzzle.
Its winter fur is long and bushy, and predominantly a mottled gray in color, although nearly pure white, red,
or brown to black also occur. As of 2005, 37 subspecies of C. lupus are recognised by MSW3.
The gray wolf is the second most specialised member of the genus Canis, after the Ethiopian wolf, as
demonstrated by its morphological adaptations to hunting large prey, its more gregarious nature, and its
highly advanced expressive behavior. It is nonetheless closely related enough to smaller Canis species, such as
the eastern wolf, coyote, and golden jackal to produce fertile hybrids. It is the only species of Canis to have
a range encompassing both the Old and New Worlds, and originated in Eurasia during the Pleistocene, colonizing
North America on at least three separate occasions during the Rancholabrean. It is a social animal, travelling
in nuclear families consisting of a mated pair, accompanied by the pair's adult offspring. The gray wolf is
typically an apex predator throughout its range, with only humans and tigers posing a serious threat to it. It
feeds primarily on large ungulates, though it also eats smaller animals, livestock, carrion, and garbage.
The gray wolf is one of the world's best known and well researched animals, with probably more books written
about it than any other wildlife species. It has a long history of association with humans, having been despised
and hunted in most pastoral communities because of its attacks on livestock, while conversely being respected
in some agrarian and hunter-gatherer societies. Although the fear of wolves is pervasive in many human
societies, the majority of recorded attacks on people have been attributed to animals suffering from rabies.
Non-rabid wolves have attacked and killed people, mainly children, but this is rare, as wolves are relatively
few, live away from people, and have developed a fear of humans from hunters and shepherds.
Anatomy and dimensions
The gray wolf is the largest extant member of the Canidae, excepting certain large breeds of domestic dog.
Gray wolf weight and size can vary greatly worldwide, tending to increase proportionally with latitude as
predicted by Bergmann's Rule, with the large wolves of Alaska and Canada sometimes weighing 3-6 times more than
their Middle Eastern and South Asian cousins. On average, adult wolves measure 105-160 cm (41-63 in) in length
and 80-85 cm (32-34 in) in shoulder height. The tail measures 29-50 cm (11-20 in) in length. The ears are 90-110
millimetres (3.5-4.3 in) in height, and the hind feet are 220-250 millimetres (8.7-9.8 in). The mean body
mass of the extant gray wolf is 40 kg (88 lb), with the smallest specimen recorded at 12 kg (26 lb) and the
largest at 80 kg (176 lb). Gray wolf weight varies geographically; on average, European wolves may weigh 38.5
kilograms (85 lb), North American wolves 36 kilograms (79 lb) and Indian and Arabian wolves 25 kilograms
(55 lb). Females in any given wolf population typically weigh 5-10 lbs less than males. Wolves weighing over
54 kg (120 lbs) are uncommon, though exceptionally large individuals have been recorded in Alaska, Canada, and
the forests of western Russia. The heaviest recorded gray wolf in North America was killed on 70 Mile River in
east-central Alaska on July 12, 1939 and weighed 79.4 kilograms (175 lb).
Compared to its closest wild cousins (the coyote and golden jackal), the gray wolf is larger and heavier, with a
broader snout, shorter ears, a shorter torso and longer tail. It is a slender, powerfully built animal with a
large, deeply descending ribcage, a sloping back and a heavily muscled neck. The wolf's legs are moderately
longer than those of other canids, which enables the animal to move swiftly, and allows it to overcome the deep
snow that covers most of its geographical range. The ears are relatively small and triangular. Females tend to
have narrower muzzles and foreheads, thinner necks, slightly shorter legs and less massive shoulders than
The gray wolf usually carries its head at the same level as the back, raising it only when alert. It usually
travels at a loping pace, placing its paws one directly in front of the other. This gait can be maintained for
hours at a rate of 8-9 km/h, and allows the wolf to cover great distances. On bare paths, a wolf can quickly
achieve speeds of 50-60 km/h. The gray wolf has a running gait of 55 to 70 km/h, can leap 5 metres horizontally
in a single bound, and can maintain rapid pursuit for at least 20 minutes.
Skull and dentition
The gray wolf's head is large and heavy, with a wide forehead, strong jaws and a long, blunt muzzle.
The skull averages 9-11 inches in length, and 5-6 inches wide. The teeth are heavy and large, being better
suited to crushing bone than those of other extant canids, though not as specialised as those found in hyenas.
Its molars have a flat chewing surface, but not to the same extent as the coyote, whose diet contains more
vegetable matter. The gray wolf's jaws can exert a crushing pressure of perhaps 10,340 kPa (1,500 psi) compared
to 5,200 kPa (750 psi) for a German shepherd. This force is sufficient to break open most bones. A study of the
estimated bite force at the canine teeth of a large sample of living and fossil mammalian predators when
adjusted for the body mass found that for placental mammals, the bite force at the canines (in Newtons/kilogram
of body weight) was greatest in the extinct dire wolf (163), then followed among the extant canids by the four
hypercarnivores that often prey on animals larger than themselves: the African hunting dog (142), the gray wolf
(136), the dhole (112), and the dingo (108).
The gray wolf has very dense and fluffy winter fur, with short underfur and long, coarse guard hairs. Most of
the underfur and some of the guard hairs are shed in the spring and grow back in the autumn period. The longest
hairs occur on the back, particularly on the front quarters and neck. Especially long hairs are on the
shoulders, and almost form a crest on the upper part of the neck. The hairs on the cheeks are elongated and
form tufts. The ears are covered in short hairs, which strongly project from the fur. Short, elastic and
closely adjacent hairs are present on the limbs from the elbows down to the calcaneal tendons. The winter fur
is highly resistant to cold; wolves in northern climates can rest comfortably in open areas at −40° by placing
their muzzles between the rear legs and covering their faces with their tail. Wolf fur provides better
insulation than dog fur, and does not collect ice when warm breath is condensed against it. In warm climates,
the fur is coarser and scarcer than in northern wolves. Female wolves tend to have smoother furred limbs than
males, and generally develop the smoothest overall coats as they age. Older wolves generally have more white
hairs in the tip of the tail, along the nose and on the forehead. The winter fur is retained longest in
lactating females, though with some hair loss around their nipples. Hair length on the middle of the back is
60-70 mm. Hair length of the guard hairs on the shoulders generally does not exceed 90 mm, but can reach
Coat color ranges from almost pure white through various shades of blond, cream, and ochre to grays, browns,
and blacks, with variation in fur color tending to increase in higher latitudes. Differences in coat color
between sexes are largely absent, though females may have redder tones. Black colored wolves in North America
inherited the Kb allele responsible for melanism from past interbreeding with dogs, while the mutation was
found to be naturally occurring in wolves from Iran. Black specimens are more common in North America than in
Eurasia, with about half the wolves in Yellowstone National Park being black.
Social and territorial behaviors
The gray wolf is a social animal, whose basic social unit consists of a mated pair, accompanied by the pair's
adult offspring. The average pack consists of a family of 5-11 animals (1-2 adults, 3-6 juveniles and 1-3
yearlings), or sometimes two or three such families, with exceptionally large packs consisting of 42 wolves
being known. In ideal conditions, the mated pair produces pups every year, with such offspring typically
staying in the pack for 10-54 months before dispersing. Triggers for dispersal include the onset of sexual
maturity and competition within the pack for food. The distance travelled by dispersing wolves varies widely;
some stay in the vicinity of the parental group, while other individuals may travel great distances of 390 km,
206 km, and 670 km from their natal packs. A new pack is usually founded by an unrelated dispersing male and
female, travelling together in search of an area devoid of other hostile packs. Wolf packs rarely adopt other
wolves into their fold, and typically kill them. In the rare cases where other wolves are adopted, the adoptee
is almost invariably an immature animal (1-3 years of age) unlikely to compete for breeding rights with the
mated pair. In some cases, a lone wolf is adopted into a pack to replace a deceased breeder. During times of
ungulate abundance (migration, calving etc.), different wolf packs may temporarily join forces.
Wolves are highly territorial animals, and generally establish territories far larger than they require to
survive in order to assure a steady supply of prey. Territory size depends largely on the amount of prey
available and the age of the pack's pups, tending to increase in size in areas with low prey populations or
when the pups reach the age of 6 months, thus having the same nutritional needs as adults. Wolf packs travel
constantly in search of prey, covering roughly 9% of their territory per day (average 25 km/d or 15 mi/d). The
core of their territory is on average 35 km2 (14 sq mi), in which they spend 50% of their time. Prey density
tends to be much higher in the territory's surrounding areas, though wolves tend to avoid hunting in the
fringes of their range unless desperate, because of the possibility of fatal encounters with neighboring packs.
The smallest territory on record was held by a pack of six wolves in northeastern Minnesota, which occupied an
estimated 33 km2 (13 sq mi), while the largest was held by an Alaskan pack of ten wolves encompassing a 6,272
km2 (2,422 sq mi) area. Wolf packs are typically settled, and usually only leave their accustomed ranges
during severe food shortages.
Wolves defend their territories from other packs through a combination of scent marking, direct attacks and
howling (see Communication). Scent marking is used for territorial advertisement, and involves urination,
defecation and ground scratching. Scent marks are generally left every 240 metres throughout the territory on
regular travelways and junctions. Such markers can last for 2-3 weeks, and are typically placed near rocks,
boulders, trees or the skeletons of large animals. Territorial fights are among the principal causes of wolf
mortality, with one study concluding that 14-65% of wolf deaths in Minnesota and the Denali National Park and
Preserve were due to predation by other wolves.
Reproduction and development
The gray wolf is generally monogamous, with mated pairs usually remaining together for life, unless one of the
pair dies. Upon the death of one mated wolf, pairs are quickly re-established. Since males often predominate in
any given wolf population, unpaired females are a rarity. If a dispersing male gray wolf is unable to establish
a territory or find a mate, he mates with the daughters of already established breeding pairs from other packs.
Such gray wolves are termed "Casanova wolves" and, unlike males from established packs, they do not form pair
bonds with the females they mate with. Some gray wolf packs may have multiple breeding females this way, as is
the case in Yellowstone National Park. Gray wolves also practice alloparental care, in which a wolf pair may
adopt the pup or pups of another. This might take place if the original parents die or are for some reason
separated from them. In addition to heterosexual behavior, homosexual behavior has been observed in gray
wolves. Male gray wolves often mount each other when the highest ranking female in the pack comes into heat.
The age of first breeding in gray wolves depends largely on environmental factors: when food is plentiful, or
when wolf populations are heavily managed, wolves can rear pups at younger ages in order to better exploit
abundant resources. This is further demonstrated by the fact that captive wolves have been known to breed as
soon as they reach 9-10 months, while the youngest recorded breeding wolves in the wild were 2 years old.
Females are capable of producing pups every year, with one litter annually being the average. Unlike the
coyote, the gray wolf never reaches reproductive senescence. Estrus typically occurs in late winter, with older,
multiparous females entering estrus 2-3 weeks earlier than younger females. During pregnancy, female wolves
remain in a den located away from the peripheral zone of their territories, where violent encounters with other
packs are more likely. Old females usually whelp in the den of their previous litter, while younger females
typically den near their birthplace. The gestation period lasts 62-75 days, with pups usually being born in the
Wolves bear relatively large pups in small litters compared to other canid species. The average litter consists
of 5-6 pups, with litter sizes tending to increase in areas where prey is abundant, though exceptionally large
litters of 14-17 pups occur only 1% of the time. Pups are usually born in spring, coinciding with a
corresponding increase in prey populations. Pups are born blind and deaf, and are covered in short soft
grayish-brown fur. They weigh 300-500 grams at birth, and begin to see after 9-12 days. The milk canines erupt
after one month. Pups first leave the den after 3 weeks. At 1.5 months of age, they are agile enough to flee
from danger. Mother wolves do not leave the den for the first few weeks, relying on the fathers to provide food
for them and their young. Pups begin to eat solid food at the age of 3-4 weeks. Pups have a fast growth rate
during their first four months of life: during this period, a pup's weight can increase nearly 30 times. Wolf
pups begin play fighting at the age of 3 weeks, though unlike young foxes and coyotes, their bites are
inhibited. Actual fights to establish hierarchy usually occur at 5-8 weeks of age. This is in contrast to young
foxes and coyotes, which may begin fighting even before the onset of play behavior. By autumn, the pups are
mature enough to accompany adults on hunts for large prey.
Hunting and feeding behaviors
Although social animals, single wolves or mated pairs typically have higher success rates in hunting than do
large packs, with single wolves having occasionally been observed to kill large prey such as moose, bison and
muskoxen unaided. The gray wolf's sense of smell is relatively weakly developed when compared to that of some
hunting dog breeds, being able to detect carrion upwind no farther than 2-3 km. Because of this, it rarely
manages to capture hidden hares or birds, though it can easily follow fresh tracks. Its auditory perception is
acute enough to be able to hear up to a frequency of 26 kHz, which is sufficient to register the fall of leaves
in the autumn period. A gray wolf hunt can be divided into five stages:
Locating prey: The wolves travel in search of prey through their power of scent, chance encounter, and tracking.
Wolves typically locate their prey by scent, though they must usually be directly downwind of it. When a
breeze carrying the prey's scent is located, the wolves stand alert, and point their eyes, ears and nose
towards their target. In open areas, wolves may precede the hunt with group ceremonies involving standing
nose-to-nose and wagging their tails. Once concluded, the wolves head towards their prey.
The stalk: The wolves attempt to conceal themselves as they approach. As the gap between the wolves and their
prey closes, the wolves quicken their pace, wag their tails, and peer intently, getting as close to their quarry
as possible without making it flee.
The encounter: Once the prey detects the wolves, it can either approach the wolves, stand its ground, or flee.
Large prey, such as moose, elk, and muskoxen, usually stand their ground. Should this occur, the wolves hold
back, as they require the stimulus of a running animal to proceed with an attack. If the targeted animal stands
its ground, the wolves either ignore it, or try to intimidate it into running.
The rush: If the prey attempts to flee, the wolves immediately pursue it. This is the most critical stage of the
hunt, as wolves may never catch up with prey running at top speed. If their prey is travelling in a group, the
wolves either attempt to break up the herd, or isolate one or two animals from it.
The chase: A continuation of the rush, the wolves attempt to catch up with their prey and kill it. When chasing
small prey, wolves attempt to catch up with their prey as soon as possible, while with larger animals, the
chase is prolonged, in order to wear the selected prey out. Wolves usually give up chases after 1-2 km
(0.62-1.3 mi), though one wolf was recorded to chase a deer for 21 km (13 mi). Both Russian and North American
wolves have been observed to drive prey onto crusted ice, precipices, ravines, slopes and steep banks to slow
The actual killing method varies according to prey species. With large prey, mature wolves usually avoid
attacking frontally, instead focusing on the rear and sides of the animal. Large prey, such as moose, is killed
by biting large chunks of flesh from the soft perineum area, causing massive blood loss. Such bites can cause
wounds 10-15 cm in length, with three such bites to the perineum usually being sufficient to bring down a large
deer in optimum health. With medium-sized prey such as roe deer or sheep, wolves kill by biting the throat,
severing nerve tracks and the carotid artery, thus causing the animal to die within a few seconds to a minute.
With small, mouse-like prey, wolves leap in a high arc and immobilize it with their forepaws. When prey is
vulnerable and abundant, wolves may occasionally surplus kill. Such instances are common in domestic animals,
but rare in the wild. In the wild, surplus killing primarily occurs during late winter or spring, when snow is
unusually deep (thus impeding the movements of prey) or during the denning period, when wolves require a ready
supply of meat when denbound. Medium-sized prey are especially vulnerable to surplus killing, as the swift
throat-biting method by which they are killed allows wolves to quickly kill one animal and move on to another.
Once prey is brought down, wolves begin to feed excitedly, ripping and tugging at the carcass in all directions,
and bolting down large chunks of it. The breeding pair typically monopolizes food in order to continue producing
pups. When food is scarce, this is done at the expense of other family members, especially non-pups. The
breeding pair typically eats first, though as it is they who usually work the hardest in killing prey, they may
rest after a long hunt and allow the rest of the family to eat unmolested. Once the breeding pair has finished
eating, the rest of the family tears off pieces of the carcass and transport them to secluded areas where they
can eat in peace. Wolves typically commence feeding by consuming the larger internal organs of their prey,
such as the heart, liver, lungs and stomach lining. The kidneys and spleen are eaten once they are exposed,
followed by the muscles. A single wolf can eat 15-19% of its body weight in a single feeding.
The gray wolf is a habitat generalist, and can occur in deserts, grasslands, forests and arctic tundras. Habitat
use by gray wolves is strongly correlated with the abundance of prey, snow conditions, absence or low livestock
densities, road densities, human presence and topography. In cold climates, the gray wolf can reduce the flow
of blood near its skin to conserve body heat. The warmth of the footpads is regulated independently of the rest
of the body, and is maintained at just above tissue-freezing point where the pads come in contact with ice
and snow. Gray wolves use different places for their diurnal rest: places with cover are preferred
during cold, damp and windy weather, while wolves in dry, calm and warm weather readily rest in the open.
During the autumn-spring period, when wolves are more active, they willingly lie out in the open, whatever
their location. Actual dens are usually constructed for pups during the summer period. When building dens,
females make use of natural shelters such as fissures in rocks, cliffs overhanging riverbanks and holes
thickly covered by vegetation. Sometimes, the den is the appropriated burrow of smaller animals such as
foxes, badgers or marmots. An appropriated den is often widened and partly remade. On rare occasions,
female wolves dig burrows themselves, which are usually small and short with 1-3 openings. The den is usually
constructed not more than 500 metres away from a water source, and typically faces southwards, thus ensuring
enough sunlight exposure, keeping the denning area relatively snow free. Resting places, play areas for the
pups and food remains are commonly found around wolf dens. The odour of urine and rotting food emanating from
the denning area often attracts scavenging birds such as magpies and ravens. As there are few convenient places
for burrows, wolf dens are usually occupied by animals of the same family. Though they mostly avoid areas within
human sight, wolves have been known to nest near domiciles, paved roads and railways.
All social terrestrial mammalian predators feed mostly on terrestrial herbivorous mammals with a body mass
similar to the combined mass of the social group members attacking the prey animal, and a pack of timber wolves
can bring down a 500 kg moose as their preferred prey. The gray wolf generally specializes in vulnerable
individuals of large prey. In Eurasia, many gray wolf populations are forced to subsist largely on livestock and
garbage in areas with dense human activity, though wild ungulates such as moose, red deer, roe deer and wild
boar are still the most important food sources in Russia and the more mountainous regions of Eastern Europe.
Other prey species include reindeer, argali, mouflon, wisent, saiga, ibex, chamois, wild goats, fallow deer
and musk deer. The prey animals of North American wolves have largely continued to occupy suitable habitats
with low human density, and cases of wolves subsisting largely on garbage or livestock are exceptional. Animals
preferred as prey by North American wolves include moose, white-tailed deer, elk, mule deer, bighorn sheep,
Dall's sheep, American bison, muskox and caribou.
Although wolves primarily feed on medium to large sized ungulates, they are not fussy eaters. Smaller sized
animals that may supplement the diet of wolves include marmots, hares, badgers, foxes, weasels, ground
squirrels, mice, hamsters, voles and other rodents, as well as insectivores. They frequently eat waterfowl and
their eggs. When such foods are insufficient, they prey on lizards, snakes, frogs, rarely toads and large
insects as available. In times of scarcity, wolves readily eat carrion, visiting cattle burial grounds and
slaughter houses. Cannibalism is not uncommon in wolves: during harsh winters, packs often attack weak or
injured wolves, and may eat the bodies of dead pack members. Wolf packs in Astrakhan hunt Caspian seals on the
Caspian Sea coastline and some wolf packs in Alaska and Western Canada have been observed to feed on salmon.
Humans are rarely, but occasionally preyed upon. Other primates occasionally taken by wolves include grey
langurs in Nepal and hamadryas baboons in Saudi Arabia.
Wolves supplement their diet with fruit and vegetable matter. They willingly eat the berries of mountain ash,
lily of the valley, bilberries, blueberries and cowberry. Other fruits include nightshade, apples and pears.
They readily visit melon fields during the summer months. A well-fed wolf stores fat under the skin, around the
heart, intestines, kidneys, and bone marrow, particularly during the autumn and winter. Digestion only takes a
few hours, thus wolves can feed several times in one day, making quick use of large quantities of meat.