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Gray Wolf

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Social structureEdit

In popular literature, wolf packs are often portrayed as strictly hierarchical social structures with a breeding "alpha" pair which climbs the social ladder through fighting, followed by subordinate "beta" wolves and a low ranking "omega" which bears the brunt of the pack's aggression. This terminology is based heavily on the behaviour of captive wolf packs composed of unrelated animals, which will fight and compete against each other for status. Also, as dispersal is impossible in captive situations, fights become more frequent than in natural settings. In the wild, wolf packs are little more than nuclear families whose basic social unit consists of a mated pair, followed by its offspring.[63] Northern wolf packs tend not to be as compact or unified as those of African wild dogs and spotted hyenas,[64] though they are not as unstable as those of coyotes.[65] Southern wolves are more similar in social behaviour to coyotes and dingoes, living largely alone or in pairs.[66] The average pack consists of 5–11 animals; 1–2 adults, 3–6 juveniles and 1–3 yearlings,[67] though exceptionally large packs consisting of 42 wolves are known. Wolf packs rarely adopt other wolves into their fold, and typically kill them. In the rare cases where strange wolves are adopted, the adoptee is almost invariably a young animal of 1–3 years of age, while killed wolves are mostly fully grown.[68] The adoption of a new member can be a lengthy process, and can consist of weeks of exploratory, non-fatal attacks in order to establish whether or not the newcomer is trustworthy.[69] During times of ungulate abundance (migration, calving etc.), different wolf packs may temporarily join forces.[70] Wolves as young as five months and as old as five years have been recorded to leave their packs to start their own families, though the average age is 11–24 months. Triggers for dispersal include the onset of sexual maturity and competition within the pack for food and breeding.[71]


Wolf nursing her pupsIn areas with low wolf densities, wolves are generally monogamous.[72] Mated pairs usually remain together for life if one of the wolves does not die. 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.[73] Polygamy does occur, but primarily in captive situations. Multiple litters are rarely successful, due to infanticide by the pack's females.[74] The age of first breeding in wolves depends largely on environmental factors; when food is abundant, or when wolf populations are heavily managed, wolves can rear pups at younger ages in order to exploit the newly available resources. 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 coyotes, wolves never reach reproductive senescence before they die.[75] Incest rarely occurs, though inbreeding depression has been reported to be a problem for wolves in Saskatchewan[76] and Isle Royale.[77]

Estrus typically occurs in late winter, with older, multiparous females entering estrus 2–3 weeks earlier than younger females. Before the rut ensues, wolf packs will temporarily dissolve until the end of the mating season.[73] When receptive, females will avert the base of their tails to one side, exposing the vulva. During mating, the pair is locked into a copulatory tie which may last 5–36 minutes. Because estrus in wolves only lasts a month, the males do not abandon their mates to find other females to inseminate as dogs do. During pregnancy, female wolves will remain in a den located away from the peripheral zone of their territories, where violent encounters with other packs are more likely.[78] 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 summer period.[79] The average litter consists of 5–6 pups. Litters of 14–17 occur 1% of the time.[80] Litter sizes tend to increase in areas where prey is abundant.[81] Wolves bear relatively large pups in small litters compared to other canid species.[82] 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.[82][83] Unlike wolf mothers, the fathers do not regurgitate the pup's food, but carry them pieces from a kill. If the mother dies prior to the pups weaning period, they are suckled by the pack's other females.[84] 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, the pup's weight can increase nearly 30 times.[82][83]

The reproductive behaviour of introduced wolf packs in Yellowstone is unusual, as they often have multiple breeding females who mate with lone male wolves that encroach upon the pack territories during the mating season. These so called "Casanova wolves" are young males that, having failed to procure mates or territories after leaving their natal pack, mate with the daughters of already established breeding pairs from other packs. Unlike males from established packs, Casanova wolves do not form pair bonds with the females they mate with. Because of the great abundance of prey in Yellowstone, female wolves there can bear multiple litters in this fashion.[85]

Denning and sheltering behaviourEdit

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 will dig burrows themselves, which are usually small and short with 1-3 openings.[86] Wolves do not line their denning places, a likely precaution against parasites.[87] The den is usually constructed not more than 500 metres away from a water source. 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.[86]

Territorial behavioursEdit

Wolves scent-roll to bring scents back to the packWolves 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: in areas with an abundance of prey, the territories of resident wolf packs are smaller. 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.[88] Prey density tends to be much higher in the territory's surrounding areas. Despite this higher abundance of prey, wolves tend to avoid hunting in the fringes of their territory unless desperate, due to the possibility of fatal encounters with neighboring packs.[89] The size of their territory may increase when the pack's pups reach the age of 6 months, and thus have the same nutritional requirements as adults. The smallest territory on record was held by a pack of six wolves in northeastern Minnesota, which occupied an estimated 33 km2. The largest was held by an Alaskan pack of ten wolves encompassing a 6,272 km2 area. In some areas, wolves may shift territories during their prey's migration season.[90]

Wolves defend their territories from other packs through a combination of scent marking, direct attacks and howling. 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,[90] and are typically placed near rocks, boulders, trees or the skeletons of large animals.[91] When scent marking and howling fail to deter strange wolf packs from entering another's territory, violent interactions can ensue.[90] Territorial fights are among the principal causes of wolf mortality: one 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.[92] In fact, 91% of wolf fatalities occur within 3.2 km (2.0 mi) of the borders between neighboring territories.[93] Because the consequences of trespassing can be fatal, such incursions are thought to be largely due to desperation or deliberate aggressiveness.[90]

Hunting and feeding behavioursEdit

An American Bison standing its ground, thereby increasing its chance of survival. A bull elk running, thereby decreasing its chance of survivalAlthough wolf packs do cooperate strategically in bringing down prey, they do not do so as frequently or as effectively as lionesses do; unlike lions, wolves rarely remain with their pack for more than two years, thus they have less time to learn how to hunt cooperatively. Contrary to lion prides, food acquisition per wolf decreases with pack size.[109] Overall, single wolves or mated pairs typically have higher success rates in hunting than do large packs. Single wolves have occasionally been observed to kill large prey such as moose, bison and muskoxen unaided.[110] When hunting, wolves will attempt to conceal themselves as they approach their prey. With ungulate herds, they then either attempt to break up the herd, or isolate one or two animals from it.[111] If the targeted animal stands its ground, the wolves either ignore it, or try to intimidate it into running.[112] When chasing small prey, wolves will attempt to catch up with their prey as soon as possible. With larger animals, the chase is prolonged, in order to wear the selected prey out.[110] 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).[32] Sometimes, a single wolf will distract the herd with its presence, acting as a decoy, while its pack mates attack from behind.[113] Wolf packs may also set up ambush trails; Indian wolves have been observed to chase gazelle herds through ravines where other wolves lie in wait within holes dug prior to the hunt,[114] while Russian wolves will set up ambushes near water holes, sometimes using the same site repeatedly.[111] Both Russian and North American wolves have been observed to drive prey onto crusted ice, precipices, ravines, slopes and steep banks to slow them down.[115] Mature wolves usually avoid attacking large prey frontally, instead focusing on the rear and sides of the animal. They kill large prey by biting large chunks of flesh from the soft perinium area, causing massive blood loss. Such bites can cause wounds 10–15 cm in length, with three such bites to the perinium usually being sufficient to bring down a large deer in optimum health.[115] When attacking moose, they occasionally bleed it to death by biting its soft nose.[99] With medium-sized prey such as roe deer or sheep, northern 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,[116] while the smaller southern wolves may grab the animal by the neck and stun it by jerking its head downward, hitting its nose on the ground.[9] 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)[117] or during the denning period, when wolves require a ready supply of meat when denbound.[118] 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.[116] Surplus killing may also occur when adult wolves are teaching their young to hunt.[119]

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.[95][120] This is in marked contrast to the feeding behaviours of dholes and African wild dogs, who give priority to their pups when feeding.[121] 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 will tear 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.[122]

Relationships with Other PredatorsEdit

Wolves typically dominate other canid species in areas where they both occur. In North America, incidences of wolves killing coyotes are common, with such incidences being especially common in winter, when coyotes feed on wolf kills. Wolves may attack coyote den sites, digging out and killing the pups. They rarely eat the coyotes they kill. There are no records of coyotes killing wolves, though coyotes may chase wolves if they outnumber them.[123][124] Near identical interactions have been observed in Eurasia between wolves and golden jackals, with the latter's numbers being comparatively small in areas with high wolf densities.[123][125][126] Wolves are the most important predator of raccoon dogs, killing large numbers of them in the spring and summer periods.[127] Wolves also kill red, arctic and corsac foxes, usually in disputes over carcasses. They may eat the foxes they kill.[128][129] In Asia, they may compete with dholes.[130]

Brown bears are encountered by wolves in both Eurasia and North America. Generally, the outcome of such encounters depends on context: brown bears typically prevail against wolves in disputes over carcasses, while wolves mostly prevail against bears when defending their den sites. Both species will kill each other's young. Wolves will eat the brown bears they kill, while brown bears seem to only eat young wolves.[131] American black bears occur solely in the Americas. Wolf interactions with black bears 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 on numerous occasions to actively seek out black bears in their dens and kill them without eating them. Unlike brown bears, black bears frequently lose against wolves in disputes over kills.[132] While encounters with brown and black bears appear to be common, polar bears are rarely encountered by wolves, though there are two records of wolf packs killing polar bear cubs.[133] Wolves will also kill the cubs of Asian black bears.[134] When attacking bears in daylight, wolf packs have been known to harry their quarry and wait till nightfall before making the final assault, as wolves have better night vision than bears.[135]

Wolves may encounter striped hyenas in Israel and Central Asia, usually in disputes over carcasses. Hyenas feed extensively on wolf-killed carcasses in areas where the two species interact. On a one-to-one basis, hyenas dominate wolves, though wolf packs can drive off single hyenas.[136]

Large wolf populations limit the numbers of small to medium sized felines. Wolves encounter cougars along portions of the Rocky Mountains and adjacent mountain ranges. Wolves and cougars typically avoid encountering each other by hunting on different elevations. In winter however, when snow accumulation forces their prey into valleys, interactions between the two species become more likely. Although they rarely interact, wolves and cougars will kill each other, with packs of the former sometimes usurping the latter's kills.[137] They hunt steppe cats, and may pose a threat to snow leopards.[138] Wolves may reduce Eurasian lynx populations.[139]

Other than humans, tigers appear to be the only serious predators of wolves.[138][140][141][142] In areas where wolves and tigers share ranges, such as the Russian Far East, the two species typically display a great deal of dietary overlap, resulting in intense competition. Wolf and tiger interactions are well documented in Sikhote-Alin, which until the beginning of the 20th century, held very few wolves. It is thought by certain experts that wolf numbers increased in the region after tigers were largely eliminated during the Russian colonization in the late 19th and early 20th centuries. This is corroborated by native inhabitants of the region claiming that they had no memory of wolves inhabiting Sikohte-Alin until the 1930s, when tiger numbers decreased. 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 latter's numbers. Today wolves are considered scarce in tiger inhabited areas, being found in scattered pockets, and usually seen traveling as loners or in small groups. First hand accounts on interactions between the two species indicate that tigers occasionally chase wolves from their kills, while wolves will scavenge from tiger kills. Tigers are not known to prey on wolves, though there are four records of tigers killing wolves without consuming them.[143] This competitive exclusion of wolves by tigers has been used by Russian conservationists to convince hunters in the Far East to tolerate the big cats, as they limit ungulate populations less than wolves, and are effective in controlling the latter's numbers.[144]


Wolves primarily feed on medium to large sized ungulates (sometimes 10–15 times larger than themselves[26]), though they are not fussy eaters. Medium and small sized animals preyed on by wolves include marmots, hares, badgers, foxes, polecats, ground squirrels, mice, hamsters, voles and other rodents, as well as insectivores. They frequently eat waterfowl (particularly during their moulting period and winter, when their greasy and fatty meat helps wolves build up their fat reserves) and their eggs.[94][95] When such foods are insufficient, they will prey on lizards, snakes, frogs, rarely toads and large insects. In times of scarcity, wolves will readily eat carrion, visiting cattle burial grounds and slaughter houses.[94] Wolf packs in Astrakhan will hunt Caspian seals on the Caspian Sea coastline.[96] Some wolf packs in Alaska and Western Canada have been observed to feed on salmon.[97] 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.[98][99][100] However, they are not known to eat their young as coyotes sometimes do.[84] Wolves will 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.[98] Wolves can survive without food for long periods; two weeks without food will not weaken a wolf's muscle activity.[35]

In Eurasia, many wolf populations are forced to subsist largely on livestock and garbage in areas with dense human activity, though wild ungulates such as moose,[105] red deer, roe deer and wild boar are still important food sources in Russia and the more mountainous regions of Eastern Europe. Other prey species include reindeer, mouflon, wisent, saiga, ibex, chamois, wild goats, fallow deer and musk deer.[106] 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 commonly preyed on by North American wolves include moose, white-tailed deer, elk, mule deer, mountain sheep and caribou.[107] In North Africa, wolves feed on various cultivated crops and vegetables and domestic animals.[108]

Body languageEdit

Postural communication in wolves is composed of a variety of facial expressions, tail positions and piloerection.[61] Aggressive or self assertive wolves are characterised by their slow and deliberate movements, high body posture and raised hackles, while submissive ones carry their bodies low, sleeken their fur and lower their ears and tail.[145] When breeding males encounter subordinate family members, they may stare at them, standing erect and still with their tails horizontal to their spine.[146] The pre-caudal scent glands may play a role in expressing aggression, as combative wolves will raise the base of their tails whilst drooping the tip, thus positioning the scent glands at the highest point.[147]

Two forms of submissive behaviour are recognised: passive and active. Passive submission usually occurs as a reaction to the approach of a dominant animal, and consists of the submissive wolf lying partly on its back and allowing the dominant wolf to sniff its anogenital area. Active submission occurs often as a form of greeting, and involves the submissive wolf approaching another in a low posture, and licking the other wolf's face.[148] Howling adult wolf at the UK Wolf Conservation TrustWhen wolves are together, they commonly endulge in behaviours such as nose pushing, jaw wrestling, cheek rubbing and facial licking. The mouthing of each other's muzzles is a friendly gesture, while clamping on the muzzle with bared teeth is a dominance display. Dominant wolves may assert themselves by straddling over a subordinate family member.[149] At a kill, wolves will protect the carcass from afar from other wolves by flattening their ears outwardly, thus indicating that they are covering something belonging to them.[150]


Wolves howl to assemble the pack (usually before and after hunts), to pass on an alarm (particularly at a den site), to locate each other during a storm or unfamiliar territory and to communicate across great distances.[151] Howling consists of a fundamental frequency which may lie between 150 and 780 Hz, and consists of up to 12 harmonically related overtones. The pitch usually remains constant or varies smoothly, and may change direction as many as four or five times.[24] Wolves from different geographic locations may howl in different fashions; the howls of European wolves are much more protracted and melodious than those of North American wolves, whose howls are louder and have a stronger emphasis on the first syllable. The two are however mutually intelligible, as North American wolves have been recorded to respond to European-style howls made by biologists.[152]

Wolf howls are generally indistinguishable from those of large dogs.[153] Male wolves give voice through an octave, passing to a deep bass with a stress on "O", while females produce a modulated nasal baritone with stress on "U". Pups almost never howl, while yearling wolves produce howls ending in a series of dog-like yelps.[154] Howls used for calling pack mates to a kill are long, smooth sounds similar to the beginning of the cry of a horned owl. When pursuing prey, they emit a higher pitched howl, vibrating on two notes. When closing in on their prey, they emit a combination of a short bark and a howl.[153] When howling together, wolves harmonize rather than chorus on the same note, thus creating the illusion of there being more wolves than there actually are.[151] Lone wolves typically avoid howling in areas where other packs are present.[155] Wolves do not respond to howls in rainy weather and when satiated.[154]

Other vocalisationsEdit

Other vocalisations of wolves are usually divided into three categories: growls, barks and whines.[156] Barking has a fundamental frequency between 320–904 Hz,[24] and is usually emitted by startled wolves. Wolves do not bark as loudly or continuously as dogs do, but will bark a few times and retreat from perceived danger.[156] In captivity, wolves may learn to bark more often if they hear dogs doing so.[157]

Growling has a fundamental frequency of 380–450 Hz,[24] and is usually emitted during food challenges. Pups commonly growl when playing. One variation of the howl is accompanied by a high pitched whine, which precedes a lunging attack.[151] Whining is associated with situations of anxiety, curiosity, inquiry and intimacy such as greeting, feeding pups and playing.[156]

Range and PopulationEdit

The gray wolf was once the world's most widely distributed mammal, living north of 15°N latitude in North America and 12°N in Eurasia.[168] Wolves tend to have difficulty adapting to human induced changes, and are often referred to as an indicator species; a species delineating an ecoregion or indicating an environmental condition such as a disease outbreak, pollution, species competition, or climate change. Wolves do not seem to be able to adapt as readily to expanding civilization the way coyotes do. While human expansion has seen an increase in the latter's numbers, it has caused a drop in those of the former.[169]

Despite not being at risk for extinction, local populations of wolves are still threatened. One such threat is genetic bottlenecking caused by population fragmentation.[163] Human populations have isolated small pockets of animals, which then suffer the effects of inbreeding. Studies have shown that the reproduction rate in wolves is strongly related to genetic diversity.[170] Isolated wolf populations are greatly affected by the introduction of the alleles of even a single additional wolf.[163]

With the exception of the Great Britain and Ireland, wolves were widespread in Europe during the 18th century. Wolves were exterminated from all central and northern European countries during the 19th century and the post World War II period. Remnant populations remain in Portugal, Spain, Italy, Greece and Finland, though Eurasian wolves have been recovering naturally in several parts of Europe; recolonising France, Germany, Sweden and Norway. The largest populations now occur in eastern Europe, primarily in Romania, the Balkans and Poland.[171]

Wolf populations generally seem to be stable or increasing in most, but not all, Bern Convention nations. Limiting factors in member nations include a lack of acceptance of wolves (particularly in areas where they have made a comeback) due to concerns on livestock and dog predation and competition with hunters. Although properly regulated wolf harvests and control have been largely accepted as compatible with maintaining wolf numbers to economically acceptable levels, overhunting and poaching are recognised as the main limiting factor in European wolf populations.[172]

With the exception of Israel and Saudi Arabia, there is little information available on wolves in the Middle East. The Arabian Peninsula is home to an estimated 300–600 wolves which, though hunted year round in all Middle Eastern countries except Israel, are relatively stable and protected by the inaccessibility of the northern mountains and central and northern deserts. In India, wolves are classed as endangered, and number an estimated 800-3,000 individuals scattered among several remnant populations. In China and Mongolia, wolves are not protected except in reserves.[173]

Wolves once ranged over much of North America north of Mexico City, save for parts of California. Today, their status varies by country, state and province. Canadian and Alaskan wolves number in thousands and are in excellent biological condition. Wolves have expanded from Canada to the northern Rocky Mountains since the 1970s, establishing themselves southward in Montana, Washington, Idaho and Wyoming. In 1994, wolves from Alberta and British Columbia were captured and introduced into Yellowstone National Park, where they had been extinct since the 1930s. A similar introduction took place in 1998 in the Apache National Forest in Arizona.[174] A small, isolated group of wolves on Isle Royale is believed to be suffering from the effects of reduced genetic variability. In 1991, the population was reduced from 50 to 12 wolves. Studies have shown that this reduction has coincided with a 50% loss of allozyme heterozygosity.[175]

The presence of wolves in Egypt, Libya and Ethiopia was confirmed in 2011, when a comparison was made between the MtDNA sequences of golden jackals, Holarctic wolves (most modern wolves are of this ancestry), the Indian wolf, and the Himalayan wolf (which are considered older lineages than the main Holarctic wolf lineage) revealed that North African wolves are more closely related to Indian and Himalayan wolves than they are to golden jackals, a species which they were associated with in the past.[176]

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