Gray Wolf

Gray Wolf Fossil range: Late Pleistocene - Recent
Iberian Wolf (Canis lupus signatus)
Conservation status
Least Concern (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora Family: Canidae Genus: Canis Species: C. lupus
Binomial name
Canis lupus Linnaeus, 1758
Range map. Green, present; red, former.

The gray wolf (Canis lupus), also known as the timber wolf or wolf, is a mammal of the order Carnivora. The gray wolf is the largest wild member of the Canidae family and an ice age survivor originating during the Late Pleistocene around 300,000 years ago.^[2] Its shoulder height ranges from 0.6 to 0.9 meters (26–36 inches) and its weight varies between 20 (sometimes even lower) and 68 kilograms. DNA sequencing and genetic drift studies indicate that the gray wolf shares a common ancestry with the domestic dog (Canis lupus familiaris) and might be its ancestor.^[3] A number of other gray wolf subspecies have been identified, though the actual number of subspecies is still open to discussion. Gray wolves play an important role as apex predators in the ecosystems they typically occupy. Gray wolves are highly adaptable and have thrived in temperate forests, deserts, mountains, tundra, taiga, grasslands and urban areas.

Though once abundant over much of North America and Eurasia, the gray wolf inhabits a very small portion of its former range because of widespread destruction of its habitat, human encroachment of its habitat, and the resulting human-wolf encounters that sparked broad extirpation. Considered as a whole, however, the gray wolf is regarded as being of least concern for extinction according to the International Union for the Conservation of Nature and Natural Resources. Today, wolves are protected in some areas, hunted for sport in others, or may be subject to extermination as perceived threats to livestock and pets.

In areas where humans and wolves have been historically sympatric, wolves have frequently featured in the folklore and mythology of many cultures throughout history in both positive and negative lights.

[edit] Physiology

[edit] Physical characteristics

Wolf weight and size can vary greatly worldwide, tending to increase proportionally with latitude as predicted by Bergmann's Rule. In general, height varies from 0.6 to .95 meters (26–38 inches) at the shoulder and weight ranges from 20 (44 lb.) to 62 (137 lb.) kilograms, which together make the gray wolf the largest of all wild canids.^[4] Although rarely encountered, extreme specimens of more than 77 kg (170 lb.) have been recorded in Alaska, Canada^[5] and Russia.^[6] The heaviest recorded wild wolf in the New World was killed in east central Alaska on July 12, 1939 and weighed 79 kg (175 lb.)^[7], while the heaviest recorded wild wolf in the Old World was killed in post WWII Russian SFSR and weighed 86 kg (189 lb.).^[6] The smallest wolves come from the Arabian Wolf subspecies, the females of which may weigh as little as 10 kg (22 lb) at maturity. Wolves are sexually dimorphic, with females in any given wolf population typically weighing 20% less than males^[8]. They also have narrower muzzles and foreheads, slightly shorter, smoother furred legs and less massive shoulders^[7]. Wolves can measure anywhere from 1.3 to 2 meters (4.5–6.5 feet) from nose to the tip of the tail, which itself accounts for approximately one quarter of overall body length.^[9]

Wolf skeleton.

Wolves are built for stamina, possessing features ideal for long-distance travel. Their narrow chests and powerful backs and legs facilitate efficient locomotion. They are capable of covering several miles trotting at about a pace of 10 km/h (6 mph), and have been known to reach speeds approaching 65 km/h (40 mph) during a chase.^[10] One female wolf was recorded to have made 7 metre bounds when chasing prey.^[6]

Wolf paws are able to tread easily on a wide variety of terrains, especially snow. There is a slight webbing between each toe, which allows them to move over snow more easily than comparatively hampered prey. Wolves are digitigrade, which, with the relative largeness of their feet, helps them to distribute their weight well on snowy surfaces. The front paws are larger than the hind paws, and have a fifth digit, the dewclaw, that is absent on hind paws.^[11] Bristled hairs and blunt claws enhance grip on slippery surfaces, and special blood vessels keep paw pads from freezing.^[12] Scent glands located between a wolf's toes leave trace chemical markers behind, helping the wolf to effectively navigate over large expanses while concurrently keeping others informed of its whereabouts.^[12] Unlike dogs and coyotes, wolves lack sweat glands on their paw pads. This trait is also present in Eastern Canadian Coyotes which have been shown to have recent wolf ancestry.^[13] Wolves in Israel are unique due to the middle two toes of their paws being fused, a trait originally thought to be unique to the African Wild Dog.^[14]

Wolves molt in late spring or early summer.

Wolves have bulky coats consisting of two layers. The first layer is made up of tough guard hairs that repel water and dirt. The second is a dense, water-resistant undercoat that insulates. The undercoat is shed in the form of large tufts of fur in late spring or early summer (with yearly variations). A wolf will often rub against objects such as rocks and branches to encourage the loose fur to fall out. The undercoat is usually gray regardless of the outer coat's appearance. Wolves have distinct winter and summer pelages that alternate in spring and autumn. Females tend to keep their winter coats further into the spring than males. North American wolves typically have longer, silkier fur than their Eurasian counterparts.^[15]

Fur coloration varies greatly, running from gray to gray-brown, all the way through the canine spectrum of white, red, brown, and black. These colors tend to mix in many populations to form predominantly blended individuals, though it is not uncommon for an individual or an entire population to be entirely one color (usually all black or all white). A multicolor coat characteristically lacks any clear pattern other than it tends to be lighter on the animal's underside. Fur color sometimes corresponds with a given wolf population's environment; for example, all-white wolves are much more common in areas with perennial snow cover. Aging wolves acquire a grayish tint in their coats. It is often thought that the coloration of the wolf's pelage serves as a functional form of camouflage. This may not be entirely correct, as some scientists have concluded that the blended colors have more to do with emphasizing certain gestures during interaction.^[7]

At birth, wolf pups tend to have darker fur and blue irises that will change to a yellow-gold or orange color when the pups are between 8 and 16 weeks old.^[16] Though extremely unusual, it is possible for an adult wolf to retain its blue-colored irises.^[17]

Adolescent wolf with golden-yellow eyes.

Wolves' long, powerful muzzles help distinguish them from other canids, particularly coyotes and golden jackals, which have more narrow, pointed muzzles. Wolves differ from domestic dogs in a more varied nature. Anatomically, wolves have smaller orbital angles than dogs (>53 degrees for dogs compared with <45 degrees for wolves) and a comparatively larger brain capacity.^[18] Larger paw size, yellow eyes, longer legs, and bigger teeth further distinguish adult wolves from other canids, especially dogs. Also, precaudal glands at the base of the tail are present in wolves but not in dogs.

Wolves and most larger dogs share identical dentition. The maxilla has six incisors, two canines, eight premolars, and four molars. The mandible has six incisors, two canines, eight premolars, and six molars.^[19] The fourth upper premolars and first lower molars constitute the carnassial teeth, which are essential tools for shearing flesh. The long canine teeth are also important, in that they hold and subdue the prey. Capable of delivering up to 10,000 kPa (1450 lbf/in²) of pressure, a wolf's teeth are its main weapons as well as its primary tools.^[7]

[edit] Reproduction and life cycle

Usually, the instinct to reproduce drives young wolves away from their birth packs, leading them to seek out mates and territories of their own. Dispersals occur at all times during the year, typically involving wolves that have reached sexual maturity prior to the previous breeding season. It takes two such dispersals from two separate packs for a new breeding pair to be formed, for dispersing wolves from the same maternal pack tend not to mate.^[20] Once two dispersing wolves meet and begin traveling together, they immediately begin the process of seeking out territory, preferably in time for the next mating season. The bond that forms between these wolves often lasts until one of them dies.^[21]

Generally, mating occurs between January and April — the higher the latitude, the later it occurs.^[21] A pack usually produces a single litter unless the breeding male mates with one or more subordinate females. During the mating season, breeding wolves become very affectionate with one another in anticipation of the female's ovulation cycle. The pack tension rises as each mature wolf feels urged to mate. During this time, the breeding pair may be forced to prevent other wolves from mating with one another.^[20] Under normal circumstances, a pack can only support one litter per year, so this dominance behavior is beneficial in the long run.

When the breeding female goes into estrus (which occurs once per year and lasts 5–14 days),^[22] she and her mate will spend an extended time in seclusion. Pheromones in the female's urine and the swelling of her vulva make known to the male that the female is in heat. The female is unreceptive for the first few days of estrus, during which time she sheds the lining of her uterus; but when she begins ovulating again, the two wolves mate.

The male wolf will mount the female firmly from behind. After achieving coitus, the two form a copulatory tie once the male's bulbus glandis—an erectile tissue located near the base of the canine penis—swells and the female's vaginal muscles tighten. Ejaculation is induced by the thrusting of the male's pelvis and the undulation of the female's cervix. The two become physically inseparable for anywhere from 10 to 30 minutes, during which the male will ejaculate multiple times.^[23] After the initial ejaculation, the male may lift one of his legs over the female such that they are standing end-to-end; this is believed to be a defensive measure. The mating ritual is repeated many times throughout the female's brief ovulation period, which occurs once per year per female—unlike female dogs, whose estrus usually occurs twice per year.

A wolf resting at the entrance to its den; also note how its coloration blends in with the environment.

The gestation period lasts between 60 and 63 days. The pups, at a weight of 0.5 kg (1 lb), are born blind, deaf, and completely dependent on their mother.^[21][4] There can be anywhere from 1 to 14 pups per litter, with the average litter size being about 4 to 6.^[24] Pups reside in the den and stay there for no longer than two months. The den is usually on high ground near an open water source, and has an open "room" at the end of an underground or hillside tunnel that can be up to a few meters long.^[12] During this time, the pups will become more independent, and will eventually begin to explore the area immediately outside the den before gradually roaming up to a mile away from it at around 5 weeks of age. Wolf growth rate is slower than that of coyotes and dholes.^[25] They begin eating regurgitated foods after 2 weeks of feeding on milk, which in wolves has less fat and more protein and arginine than dog milk.^[8] By this time, their milk teeth have emerged — and are fully weaned by 10 weeks. During the first weeks of development, the mother usually stays with her litter alone, but eventually most members of the pack will contribute to the rearing of the pups in some way.^[21]

After two months, the restless pups will be moved to a rendezvous site, where they can stay safely while most of the adults go out to hunt. One or two adults stay behind to ensure the safety of the pups. After a few more weeks, the pups are permitted to join the adults if they are able, and will receive priority on anything killed, their low ranks notwithstanding. Letting the pups fight for eating privileges results in a secondary ranking being formed among them, and allows them to practice the dominance/submission rituals that will be essential to their future survival in pack life.^[21] During hunts, the pups remain ardent observers until they reach about 8 months of age, by which time they are large enough to participate actively.

Wolves typically reach sexual maturity after two or three years, at which point many of them will be compelled to leave their birth packs and seek out mates and territories of their own.^[21][26] Wolves that reach maturity generally live 6 to 8 years in the wild, although in captivity they can live to twice that age.^[24] High mortality rates give them a low overall life expectancy. Pups die when food is scarce; they can also fall prey to predators such as bears, or, less often, coyotes, or other wolves. The most significant causes of mortality for grown wolves are hunting and poaching, car accidents, and wounds inflicted while hunting prey. Although adult wolves may occasionally be killed by other predators, rival wolf packs are often their most dangerous non-human enemy. A study on wolf mortality in Minnesota and the Denali National Park and Preserve concluded that 14–65% of wolf deaths were due to predation by other wolves.^[27]

[edit] Diseases

Diseases recorded to be carried by wolves include rabies, brucella, deerfly fever, listerosis, foot and mouth disease and anthrax. Wolves are major hosts for rabies in Russia, Iran, Afghanistan, Iraq and India. Wolves in Russia have been recorded to carry over 50 different kinds of harmful parasites, including echinococcia, cysticercocci and coenuri. Despite their habit of carrying harmful diseases, large wolf populations are not heavily regulated by epizootic outbreaks as with other social canids. This is largely due to the habit of infected wolves vacating their packs, thus preventing mass contagion.^[6]

[edit] Behavior

[edit] Social structure

Wolves function as social predators and hunt in packs organized according to strict, rank-oriented social hierarchies.^[21] It was originally believed that this comparatively high level of social organization was related to hunting success, and while this still may be true to a certain extent, emerging theories suggest that the pack has less to do with hunting and more to do with reproductive success.

The pack is led by the two breeding individuals that sit atop the social hierarchy. The breeding pair has the greatest amount of social freedom compared to the rest of the pack. Although they are not "leaders" in the human sense of the term, they help to resolve any disputes within the pack, have the greatest amount of control over resources (such as food), and have exclusive rights to mating. While most breeding pairs are monogamous, there are exceptions.^[28] An alpha animal may preferentially mate with a lower-ranking animal, especially if the other alpha is closely related (a brother or sister, for example). The death of one breeding wolf does not affect the status of the other, who will quickly take another mate.^[21] Usually, only the breeding pair is able to rear a litter of pups successfully. Other wolves in a pack may breed, but when resources are limited, time, devotion, and preference will be given to the alpha pair's litter. Therefore, non-alpha parents of other litters within a single pack may lack the means to raise their pups to maturity of their own accord. All wolves in a pack assist in raising wolf pups. Some mature individuals choosing not to disperse may stay in their original packs so as to reinforce it and help rear more pups.

A wolf pack in Yellowstone National Park, with the breeding animals leading and the omega in the rear.

After the breeding pair, there may also be a beta wolf whose rank is above that of the others save for the breeding pair. Betas typically assume a more prominent role in assisting with the upbringing of the breeding pair's litter, often serving as surrogate mothers or fathers while the breeding pair is away. Beta wolves are the most likely to challenge their superiors for the role of dominance, though some betas seem content with being second, and will sometimes even let lower ranking wolves leapfrog them for the position of breeding animal should circumstances necessitate such a happening, such as the death of the previous breeding animal. More ambitious beta wolves, however, will only wait so long before contending for breeding position unless they choose to disperse and create their own pack instead.

Loss of rank can happen gradually or suddenly. An older wolf may simply choose to give way when a motivated challenger presents itself, yielding its position without bloodshed. On the other hand, the challenged individual may choose to fight back with varying degrees of intensity. While the majority of wolf aggression is ritualized and non-injurious, a high-stakes fight can easily result in injury for either or both parties. The loser of such a confrontation is frequently chased away from the pack or, rarely, may be killed as other aggressive wolves contribute to the insurgency. These types of confrontations are more common during the mating season. Deaths occasionally happen, with some dominant male wolves having been known to kill two to four wolves in his lifetime.^[29]

Rank order within a pack is established and maintained through a series of ritualized fights and posturing best described as "ritual bluffing". Wolves prefer ritualised displays of aggression to physical confrontations, meaning that high-ranking status is based more on personality or attitude than on size or physical strength. Rank, who holds it, and how it is enforced varies widely between packs and between individual animals. In large packs full of easy going wolves or in a group of juvenile wolves, rank order may shift almost constantly, or even be circular (for instance, animal A dominates animal B, who dominates animal C, who dominates animal A).

In a more typical pack, only one wolf will assume the role of the omega: the lowest-ranking member of a pack.^[30] Omegas receive the most aggression from the rest of the pack, and may be subjected to different forms of truculence at any time—anything from constant dominance from other pack members to inimical, physical harassment. Submissive individuals are better suited for constant displays of active and passive submission than they are for living alone. Any form of camaraderie is preferable to solitude and, indeed, submissive wolves tend to choose low rank over potential starvation. Despite the aggression to which they are often subjected, omega wolves have also been observed to be among the most playful wolves in the pack, often enticing all of the members in a pack into chasing games and other forms of play. In general, omega wolves exist to help relieve pack tension.

The size of the pack may change over time and is controlled by several factors, including habitat, personalities of individual wolves within a pack, and food supply. Packs can contain between 2 and 20 wolves, though 8 is a more typical size.^[31] New packs are formed when a wolf leaves its birth pack, finds a mate, and claims a territory. Lone wolves searching for other individuals can travel very long distances seeking out suitable territories. Dispersing individuals must avoid the territories of other wolves because intruders on occupied territories are chased away or killed.

Wolves acting unusually within the pack, such as epileptic pups or thrashing adults crippled by a trap or a gunshot, are usually killed by other members of their own pack.^[7]

[edit] Body language

See also: Dog communication

This facial expression is defensive and gives warning to other wolves to be cautious.

This facial expression shows fear.

Wolves can communicate visually through a wide variety of expressions and moods ranging from subtle signals, such as a slight shift in weight, to more obvious ones, such as rolling on their backs to indicate complete submission.^[32]

• Dominance – A dominant wolf stands stiff legged and tall. The ears are erect and forward, and the hackles bristle slightly. Often the tail is held vertically and curled toward the back. This display asserts the wolf's rank to others in the pack. A dominant wolf may stare at a submissive one, pin it to the ground, "ride up" on its shoulders, or even stand on its hind legs.
• Submission (active) – During active submission, the entire body is lowered, and the lips and ears are drawn back. Sometimes active submission is accompanied by muzzle licking, or the rapid thrusting out of the tongue and lowering of the hindquarters. The tail is placed down, or halfway or fully between the legs, and the muzzle often points up to the more dominant animal. The back may be partly arched as the submissive wolf humbles itself to its superior; a more arched back and more tucked tail indicate a greater level of submission.
• Submission (passive) – Passive submission is more intense than active submission. The wolf rolls on its back and exposes its vulnerable throat and underside. The paws are drawn into the body. This posture is often accompanied by whimpering.
• Anger – An angry wolf's ears are erect, and its fur bristles. The lips may curl up or pull back, and the incisors are displayed. The wolf may also arch its back, lash out, or snarl.
• Fear – A frightened wolf attempts to make itself look small and less conspicuous; the ears flatten against the head, and the tail may be tucked between the legs, as with a submissive wolf. There may also be whimpering or barks of fear, and the wolf may arch its back.
• Defensive – A defensive wolf flattens its ears against its head.
• Aggression – An aggressive wolf snarls and its fur bristles. The wolf may crouch, ready to attack if necessary.
• Suspicion – Pulling back of the ears shows a wolf is suspicious. The wolf also narrows its eyes. The tail of a wolf that senses danger points straight out, parallel to the ground.
• Relaxation – A relaxed wolf's tail points straight down, and the wolf may rest sphinx-like or on its side. The wolf may also wag its tail. The further down the tail droops, the more relaxed the wolf is.
• Tension – An aroused wolf's tail points straight out, and the wolf may crouch as if ready to spring.
• Happiness – As dogs do, a wolf may wag its tail if in a joyful mood. The tongue may loll out of the mouth.
• Hunting – A wolf that is hunting is tensed, and therefore the tail is horizontal and straight.
• Playfulness – A playful wolf holds its tail high and wags it. The wolf may frolic and dance around, or bow by placing the front of its body down to the ground, while holding the rear high, sometimes wagged. This resembles the playful behavior of domestic dogs.

[edit] Howling and other vocalisations

Howling adult wolf at the UK Wolf Conservation Trust

Howling helps pack members keep in touch, allowing them to communicate effectively in thickly forested areas or over great distances. Howling also helps to call pack members to a specific location. Howling can also serve as a declaration of territory, as shown in a dominant wolf's tendency to respond to a human imitation of a "rival" wolf in an area the wolf considers its own. This behavior is stimulated when a pack has something to protect, such as a fresh kill. As a rule of thumb, large packs will more readily draw attention to themselves than will smaller packs. Adjacent packs may respond to each others' howls, which can mean trouble for the smaller of the two. Wolves therefore tend to howl with great care.^[33] Wolves will also howl for communal reasons. Some scientists speculate that such group sessions strengthen the wolves' social bonds and camaraderie—similar to community singing among humans.^[33] During such choral sessions, wolves will howl at different tones and varying pitches, making it difficult to estimate the number of wolves involved. This confusion of numbers makes a listening rival pack wary of what action to take. For example, confrontation could be disastrous if the rival pack gravely underestimates the howling pack's numbers. A wolf's howl may be heard from up to ten miles away, depending on weather conditions. Observations of wolf packs suggest that howling occurs most often during the twilight hours, preceding the adults' departure to the hunt and following their return. Studies also show that wolves howl more frequently during the breeding season and subsequent rearing process. The pups themselves begin howling soon after emerging from their dens and can be provoked into howling sessions easily over the following two months. Such indiscriminate howling usually is intended for communication, and does not harm the wolf so early in its life.^[33] Howling becomes less indiscriminate as wolves learn to distinguish howling pack members from rival wolves. The Arabian and Iranian wolf subspecies are unusual as they are not known to howl.^[7][34]

Growling, while teeth are bared, is the most visual warning wolves use. Wolf growls have a distinct, deep, bass-like quality, and are often used to threaten rivals, though not necessarily to defend themselves. Wolves also growl at other wolves while being aggressively dominant. Wolves bark when nervous or when they want to warn other wolves of danger but do so very discreetly and will not generally bark loudly or repeatedly as dogs do. Instead they use a low-key, breathy "whuf" sound to immediately get attention from other wolves. Wolves also "bark-howl" by adding a brief howl to the end of a bark. Wolves bark-howl for the same reasons they normally bark. Generally, pups bark and bark-howl much more frequently than adults, using these vocalizations to cry for attention, care, or food. A lesser known sound is the rally. Wolves will gather as a group and, amidst much tail-wagging and muzzle licking, emit a high-pitched wailing noise interspersed with something similar to (but not the same as) a bark. Rallying is often a display of submission to an alpha by the other wolves.^[35] Wolves also whimper, usually when submitting to other wolves. Wolf pups whimper when they need a reassurance of security from their parents or other wolves.

[edit] Scent marking

Wolves scent-roll to bring scents back to the pack.

Wolves, like other canines, use scent marking to lay claim to anything—from territory to fresh kills.^[30] Alpha wolves scent mark the most often, with males doing so more than females. The most widely used scent marker is urine. Male and female alpha wolves urine-mark objects with a raised-leg stance (all other pack members squat) to enforce rank and territory. They also use marks to identify food caches and to claim kills on behalf of the pack. Defecation markers are used for the same purpose as urine marks, and serve as a more visual warning, as well.^[30] Defecation markers are particularly useful for navigation, keeping the pack from traversing the same terrain too often and also allowing each wolf to be aware of the whereabouts of its pack members. Above all, though, scent marking is used to inform other wolves and packs that a certain territory is occupied, and that they should therefore tread cautiously.

Wolves have scent glands all over their bodies, including at the base of the tail, between toes, and in the eyes, genitalia, and skin.^[30] Pheromones secreted by these glands identify each individual wolf. A dominant wolf will "rub" its body against subordinate wolves to mark such wolves as being members of a particular pack. Wolves may also "paw" dirt to release pheromones instead of urine marking.^[36]

[edit] Dietary habits

Packs of wolves hunt any large herbivores in their range. Pack hunting revolves around the chase, as wolves are able to run for long periods before relenting. It takes careful cooperation for a pack to take down large prey, and the rate of success for such chase is very low. Wolves, in the interest of saving energy, will only chase one potential prey for the first thousand or so meters before giving up and trying at a different time against a different prey.^[37] Wolf packs show little strategic cooperation in hunting unlike lionesses, though wolf pairs have been shown to strategize when attacking large prey.^[8]

An American Bison standing its ground, thereby increasing its chance for survival.

Wolves feed primarily on medium to large sized ungulates, including sheep, goats, chamois, pigs, deer, antelope, caribou, horses, moose, yak, and bison. The American Bison is probably the heaviest land animal wolves prey on — bison weighing more than a ton having been taken down by a pack. Other recorded large prey include marine mammals such as seals^[6] and beached whales.^[38] Solitary wolves depend more on smaller animals, which they capture by pouncing and pinning with their front paws, though lone wolves have been recorded to bring down prey as large as bison unaided.^[8] Some wolf packs in Alaska have been observed to feed on salmon.^[39] They also prey on rodents, game birds and other small animals in a limited manner, as a typical adult wolf requires a minimum of 1.1 kg (2.5 lb) of food each day for sustenance, and approximately 2.2 kg (5lb) to reproduce successfully.^[24] Wolves rarely eat each day, but compensate by eating up to 10 kg (22 lb) at a time.^[24] Wolves will on occasion supplement their diet with vegetation, with some areas of the former Soviet Union reporting that wolves cause serious damage to watermelon plantations.^[6]

Wolves typically kill large prey by tearing at their haunches and perinium areas, causing massive bleeding. A single bite can cause a wound up to 10-15 cm in length. A large deer in optimum health will succumb to three bites at the perinium area after a chase of 150 metres. Once the prey collapses, the wolves will tear open the abdominal cavity and commence feeding on the animal, sometimes whilst it is still alive.^[6] The breeding pair usually eat first. The heart, liver and lungs are usually eaten first. The stomach is eaten, though the contents are left untouched. The leg muscles are eaten next, with the hide and bones being the last to be eaten.^[8] Though commonly portrayed as targetting solely sick or infirm animals^[26], there is little evidence that they limit themselves to such targets. Research from the former Soviet Union for example shows that in some cases, 93% of all killed prey have no illnesses or infirmities. In the Nenets Autonomous Okrug, wolves were shown to select pregnant female domestic caribou and calves rather than infirm specimens, with some reports showing that wolves bypassed emaciated, sickly animals altogether in favour of well fed ones.^[6] However, most healthy, fit individuals will not run from wolves and will instead choose to stand their ground, thus increasing the possibility of injury to the attacking wolves. The wolves are more likely to yield when confronted by bold prey. Wolves are generally inefficient at killing large, assertive prey, with success rates as low as 20% which is due, in part, to the large size and defensive capabilities of their prey.^[40]

Wolves have on occasion been observed to engage in acts of surplus killing. An instance of surplus killing by wolves was witnessed in Canada's Northwest Territories by researchers coming across 34 neonatal caribou calves, scattered over three square kilometres. The wolves had eaten only a few parts from half the calves and not touched the rest. Wolves sometimes only eat a part of their surplus-killed prey, like the tail or the internal organs. However, conditions in nature which favour surplus killing are unusual. Consequently surplus killing in the wild is rare, though fairly common in domestic situations in which the prey animals are usually confined and unable to escape the attackers.^[41] Surplus killing in the wild peaks in winter months when heavy snow impedes the movements of large hooved prey.^[6]

In certain localities in Eurasia where there is little natural prey, wolves will forage in garbage dumps. There are few cases of wolves in North America relying on garbage for food.^[8]

[edit] Interspecific predatory relationships

Wolves typically dominate other canid species in areas where they are sympatric. In North America, wolves are generally intolerant of coyotes in their territory; two years after their re-introduction to the Yellowstone National Park, the wolves were responsible for a near 50% drop in coyote populations through both competition and predation.^[42] Wolves have been reported to dig coyote pups from their dens and kill them. Wolves typically do not consume the coyotes they kill. There are no records of coyotes killing wolves^[8], though they have been known to gang up on wolves if they outnumber them.^[42] Near identical interactions have been observed in Greece between wolves and golden jackals.^[43] Wolves may kill foxes, though not as frequently as they do with coyotes. Racoon dogs are also reportedly prey upon.^[8]

Cougars are encountered in North America. Wolves are usually hostile toward cougars and will kill kittens if given the opportunity. The wolf's relation to adult cougars is more complex. A pack often takes advantage of cougars, stealing kills and sometimes killing mature adults. Interactions between solitary wolves and cougars are rarer, but the two species have killed each other.^[44] National Park Service cougar specialist Kerry Murphy stated that the cougar usually is at an advantage on a one to one basis, considering it can effectively use its claws, as well as its teeth, unlike the wolf which relies solely on its teeth. Yellowstone officials have reported that attacks between cougars and wolves are not uncommon. Multiple incidents of cougars taking wolves and vice versa have been recorded in Yellowstone National Park. However, researchers in Montana have found that wolves regularly kill cougars in the area, though they did not specify whether or not this was a pack situation.^[45]

Reconstruction of a wolf pack confronting a Grizzly bear by Adolph Murie (1944)

Brown bears are encountered in both Eurasia and North America. The majority of interactions between wolves and brown bears usually amount to nothing more than mutual avoidance. Serious confrontations depend on the circumstances of the interaction, though the most common factor is defence of food and young. Brown bears will use their superior size to intimidate wolves from their kills and when sufficiently hungry, will raid wolf dens. Brown bears usually dominate wolves on kills, though they rarely prevail against wolves defending den sites. Wolves in turn have been observed killing bear cubs, to the extent of even driving off the defending mother bears.^[8] Deaths in wolf/bear skirmishes are considered very rare occurrences, the individual power of the bear and the collective strength of the wolf pack usually being sufficient deterrents to both sides.^[46] American black bears occur solely in the Americas, and interactions with wolves are much rarer than with brown bears, due to differences in habitat preferences. The majority of black bear encounters with wolves occur in the species' northern range, with no interactions being recorded in Mexico. Wolves have been recorded to kill black bears on numerous occasions without eating them. Unlike brown bears, black bears frequently lose against wolves in disputes over kills.^[8]

In areas where wolves and tigers share ranges such as the Russian Far East, tigers depress wolf numbers, either to the point of localized extinction or to such low numbers as to make them a functionally insignificant component of the ecosystem. Wolves appear capable of escaping competitive exclusion from tigers only when human persecution decreases the latters numbers.^[47]

Wolves may occasionally encounter striped hyenas in the Middle East, Central and Southern Asia, mostly in disputes over carcasses. Though hyenas usually dominate wolves on a one to one basis, wolf packs have been reported to displace lone hyenas from carcasses.^[48] Wolf remains have been found in cave hyena den sites, though it is unknown if the wolves were killed or scavenged upon.^[49]

[edit] Taxonomy

The gray wolf is a member of the genus Canis, which comprises between 7 and 10 species. It is one of six species termed 'wolf', the others being the Red Wolf (Canis rufus), the Indian Wolf (Canis indica), the Himalayan Wolf (Canis himalayaensis), the Eastern Wolf (Canis lycaon) and the Ethiopian Wolf (Canis simensis), although concerning a couple of these there is still some uncertainty as to whether they should be considered subspecies of Canis lupus or species in their own right. Recent genetic research suggests that the Indian Wolf, originally considered only as a subpopulation of the Southern-East Asian Wolf (Canis lupus pallipes), represents a distinct species (Canis indica). Similar results were obtained for the Himalayan wolf, which is traditionally placed into the Tibetan Wolf (Canis lupus laniger) ^[50].

With respect to common names, spelling differences result in the alternative spelling grey wolf. As the first-named and most widespread of species termed "wolf", gray wolves are often simply referred to as wolves. It was one of the many species originally described by Carolus Linnaeus in his eighteenth-century work, Systema Naturae, and it still bears its original classification, Canis lupus.^[51] The binomial name is derived from the Latin Canis, meaning "dog", and lupus, "wolf".^[52]

Desert dwelling grey wolf subspecies, such as this Arabian wolf, tend to be smaller than their more northern cousins.

Current theories propose that the gray wolf first evolved in Eurasia during the early Pleistocene. The rate of changes observed in DNA sequence date the Asiatic lineage to about 800,000 years, as opposed to the American and European lineages which stretch back only 150,000.^[54] The gray wolf then migrated into North America from the Old World, probably via the Bering land bridge (that once joined Alaska and Siberia), around 400,000 years ago. The gray wolf then coexisted with the Dire Wolf (Canis dirus), a Canid species that was larger and heavier than the gray wolf and appeared in South America over 700,000 years ago and whose origin is still speculated. The Dire Wolf ranged from southern Canada to South America until about 8,000 years ago when climate changes are thought to have caused it to become extinct. After that the gray wolf is thought to have become the prime canine predator in North America.

[edit] Subspecies

Main article: Subspecies of the Gray Wolf

At one point, up to 50 gray wolf subspecies were recognized. Though no true consensus has been reached, this list can be condensed to 13–15 general extant subspecies. Modern classifications take into account the DNA, anatomy, distribution, and migration of various wolf colonies.

[edit] Disputed subspecies

Historically, gray wolf classification has been transient in nature. As a result, there still exists some disagreement as to the status of certain possible subspecies. These are listed below.

[edit] Extinct subspecies

[edit] Disputed species

[edit] Relation to the dog

Main article: Origin of the domestic dog

Comparative drawing of dog and wolf anatomy by Ernest Thompson Seton. Note the proportionately larger head of the wolf

Much debate has centered on the relationship between the wolf and the domestic dog, though most authorities see the wolf as the dog's direct ancestor. Because the canids have evolved recently and different canids interbreed readily, untangling the relationships has been difficult. However, molecular systematics now indicate very strongly that domestic dogs and wolves are closely related, and the domestic dog is now normally classified as a subspecies of the wolf: Canis lupus familiaris. All skeletal dog remains found from the upper Paleolithic and Mesolithic periods are from relatively small specimens, therfore pointing to either the Arabian or Iranian wolf as the most likely progenitor.^[56] North American domestic dogs are believed to have originated from Old World wolves. No known dog breed is derived from wolves indigenous to North America. The first people to colonize North America 12,000 to 14,000 years ago brought their dogs with them from Asia, and apparently did not separately domesticate the wolves they found in the New World.^[57]

Compared to equally sized wolves, dogs tend to have 20% smaller skulls and 10% smaller brains, as well as proportionately smaller teeth than other canid species.^[13] The premolars and molars of a dog are much more crowded and compacted than those of a wolf. Dog's teeth also have less complex cusp patterns, and their tympanic bulla is much smaller than in wolves.^[56] Dogs require fewer calories to function than wolves. The dog's diet of human refuse in antiquity made the large brains and jaw muscles needed for hunting unnecessary. It is thought by certain experts that the dog's limp ears are a result of atrophy of the jaw muscles.^[13] The paws of a dog are half the size of those of a wolf, and their tails tend to curl upwards, another trait not found in wolves.^[7] Dogs are not monogamous, and breeding in feral packs is not restricted to a dominant breeding pair. Male dogs differ from male wolves by the fact that they play no role in raising their puppies, and do not kill the young of other females to increase their own reproductive success.^[18] Dogs differ also from wolves by the fact that they do not regurgitate food for their young, nor the young of other dogs in the same territory.^[13]

[edit] Interpecific hybridization

Main article: Canid hybrid

A wolf-dog hybrid with malamute ancestry

Wolves can interbreed with domestic dogs and produce fertile offspring. Wolf-dog hybrids are generally said to be naturally healthy animals, and are affected by less inherited diseases than most breeds of dog. Wolfdogs are usually healthier than either parent due to heterosis.^[58] According to the National Wolfdog Alliance, 40 U.S. states effectively forbid the ownership, breeding and importation of wolfdogs, while others impose some form of regulation upon ownership.^[59] Most European nations, as well as many U.S. counties and municipalities, also either outlaw the animal entirely or put restrictions on ownership.^[60][61]. Although wolves in the wild will usually kill dogs, matings of dogs and wild wolves has been confirmed in some populations through genetic testing. As the survival of most Continental wolf packs is severely threatened, scientists fear that the creation of wolf-dog hybrid populations in the wild is a threat to the continued existence of some isolated wolf p