The gray wolf or grey wolf (Canis lupus) is a canid native to the wilderness and remote areas of North America, Eurasia, and North Africa. It is the largest member of its family, with males averaging 43–45 kg (95–99 lb), and females 36–38.5 kg (79–85 lb).[3] It is similar in general appearance and proportions to a German shepherd,[4] or sled dog, but has a larger head, narrower chest, longer legs, straighter tail, and bigger paws.[5] Its winter fur is long and bushy, and predominantly a mottled gray in colour, although nearly pure white, red, or brown to black also occur.[4]
Within the genus Canis, the gray wolf represents a more specialised and progressive form than its smaller cousins (the coyote and golden jackal), as demonstrated by its morphologicaladaptations to hunting large prey, its more gregarious nature,[6] and its highly advanced expressive behavior.[7][8] It is a social animal, travelling in nuclear families consisting of a mated pair, accompanied by the pair's adult offspring.[9] The gray wolf is typically an apex predator throughout its range, with only humans and tigers[10][11][12][13] posing a serious threat to it. It feeds primarily on large ungulates, though it also eats smaller animals, livestock, carrion, and garbage.[14]
The gray wolf is one of the world's most well known and well researched animals, with probably more books written about it than any other wildlife species.[15] It has a long history of association with humans, having been despised and hunted in most agricultural communities due to its attacks on livestock, while conversely being respected by some Native American tribes.[14] It is the sole ancestor of the dog,[16] which was first domesticated in the Middle East.[17][18][19] Although the fear of wolves is prevalent 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 unusual, as wolves are relatively few, live away from people, and have been taught to fear humans by hunters and shepherds.[20] Hunting and trapping has reduced the species' range to about one third of its original range, though its still relatively widespread range and stable population means that the species is not threatened at a global level, and is therefore classified by the IUCN as Least Concern.[1]
Contents
[show]Etymology
The English word "wolf" stems from the Old English wulf, which is itself thought to be derived from the Proto-Germanic *wulfaz, from the Proto-Indo-European root *wlqwos/*lukwos.[21] Old English literature contains several instances of Anglo-Saxon kings and warriors taking on wulf as a prefix or suffix in their names. Examples include Wulfhere, Cynewulf, Ceonwulf, Wulfheard, Earnwulf, Wulfmǣr, Wulfstān and Æthelwulf. Wolf-related names were also common among pre-Christian Germanic warriors: Wolfhroc (Wolf-Frock), Wolfhetan (Wolf Hide), Isangrim (Grey Mask), Scrutolf (Garb Wolf), Wolfgang (Wolf Gait) and Wolfdregil (Wolf Runner).[22]
Evolution and taxonomy
Origins
Ancestry
The species' most likely ancestral candidate is Canis lepophagus, a small, narrow skulled North American canid of the Miocene era, which may have also given rise to the coyote.[23] After the extinction of the large bodied Borophaginae family, C. lepophagus developed into a larger, broader-skulled animal. Fossils of this larger form of C. lepophagus found in northern Texas may represent the ancestral stock from which true wolves derive.[24] The first true wolves began to appear at the end of the Blancan North American Stage and the onset of the early Irvingtonian. Among them was C. priscolatrans, a small species closely resembling the modern-day red wolf, which colonised Eurasia by crossing the Bering land bridge. The new Eurasian C. priscolatrans population gradually evolved into C. mosbachensis,[23] which closely resembled modern wolves found in the Arabian Peninsula and South Asia, which were once distributed in Europe in the early Quaternary glaciation until about 500,000 years ago (seeSubspecies).[25] C. mosbachensis subsequently evolved in the direction of C. lupus.[23]
Subspeciation
MtDNA studies have shown that there are at least four distinct gray wolf lineages: the most ancient is that of the African wolf (native to North, West, and East Africa), which is thought to have originated as early as the Middle to Late Pleistocene.[26] All other lineages occur together in the Indian Subcontinent, the oldest of which is the Himalayan wolf (native to the Himalayan region of eastern Kashmir, Himachal Pradesh, parts of Tibet and eastern Nepal), which is thought to have originated 800,000 years ago, when the Himalayan region was going through major geologic and climatic upheaval. The peninsular Indian wolf, C. l. pallipes, likely diverged from the Himalayan wolf 400,000 years ago.[27][28] The youngest wolf lineage in India is represented by C. l. chanco (native to the northwestern Himalayan region of Kashmir), which originated 150,000 years ago. This last lineage, known as the Holarctic clade, expanded into Europe and North America, as shown by it sharing genetic markers with domestic dogs, European and North American wolves.[27][28]
The now extinct Japanese wolves were descended from large Siberian wolves which colonised the Korean Peninsula and Japan, before it separated from mainland Asia, 20,000 years ago during the Pleistocene. During the Holocene, the Tsugaru Strait widened and isolated Honshu from Hokkaidō, thus causing climatic changes leading to the extinction of most large bodied ungulates inhabiting the archipelago. Japanese wolves likely underwent a process of island dwarfism 7,000–13,000 years ago in response to these climatological and ecological pressures. C. l. hattai(formerly native to Hokkaidō) was significantly larger than its southern cousin C. l. hodophilax, as it inhabited higher elevations and had access to larger prey, as well as a continuing genetic interaction with dispersing wolves from Siberia.[29]
Colonization of North America
Canis lupus colonized North America during the late Rancholabrean era.[30] The larger Canis dirus was already established there, but it became extinct 8,000 years ago, after the large prey it relied on disappeared. Competition with the newly arrived gray wolf for the smaller and swifter prey that survived may have contributed to its decline. With the extinction of the dire wolf, the gray wolf became the only large and widespread canid species left.[23] The North American recolonisation likely occurred in several waves, with the most distinctive populations occurring in the periphery of the range. These populations (C. l. arctos on the high arctic islands, C. l. lycaon in the eastern forests, and C. l. baileyi in the far south) may represent survivors of early migrations from Eurasia. C. l. baileyi and C. l. lycaon display some primitive traits and systematic affinity to one another. Fossil remains from the late Pleistocene of large bodied wolves similar to C. l. arctos and C. l. albus occur in coastal southern California, indicating that large North American gray wolf subspecies were once widespread, and may have been driven southward by glaciation, though wolves no longer reside there. Fossils of small bodied wolves similar to C. l. baileyi have been found in a range encompassing Kansas and southern California. This indicates a late Pleistocene population flux, in which large, Arctic forms of wolf moved farther south, with smaller, warmth adapted wolves expanding as the climate moderated.[30]
Subspecies
Main article: Subspecies of Canis lupus
As of 2005,[31] 37 subspecies of gray wolf are recognised by MSW3. Included among them are the domestic dog and the dingo, as well as the Eastern wolf ofAlgonquin Provincial Park and the red wolf of North Carolina. Once thought to be unique species, SNP studies show that the red and Eastern wolf are in fact the results of varying degrees of wolf–coyote hybridization stretching back to only a few centuries. The Eastern wolf is on average 58% gray wolf, while the red wolf is only 20–24%.[32] Phylogenetic comparisons of the MtDNA sequences of both wolves and golden jackals in 2011 demonstrated that the African wolf, which was once thought to be a golden jackal, is in fact a subspecies of gray wolf.[33]
Wolf subspecies are divided into two categories:
- "Northern wolves": large-sized, large-brained wolves with strong carnassials which inhabit North America, Europe and northern Asia.[34]
- "Southern wolves": native to the Arabian Peninsula, South Asia and possibly North Africa. They are characterised by their smaller size, skull and teeth, and a short and thin coat without appreciable underwool.[35] They may represent a relict population of early wolves, as they closely resemble fossil European wolves.[25]The rate of changes observed in their DNA sequences date them to about 800,000 years, as opposed to the American and European lineages which stretch back only 150,000.[36] The vocalisations of southern wolves have a higher proportion of short, sharp barking,[34] and they seldom howl.[37] It is likely that dogs anddingoes stem from this group.[34][38]
Wolves in Central and East Asia are intermediate in form and size to northern and southern wolves.[25] Differences in brain size are well defined in different wolf populations, with wolves in northern Eurasia having the highest values, North American wolves having slightly smaller brains, and the southern wolves having the smallest (about 5–10% smaller than those of northern wolves).[39]
Domestication
Main article: Origin of the domestic dog
Morphological comparisons between wolves and domestic dogs have narrowed the likely ancestral subspecies of gray wolf to Middle Eastern and South Asian wolves.[25] This is confirmed bySNP studies done in 2010, which point to the Middle East as the source of most of the genetic diversity in the domestic dog and the most likely origin of domestication events.[17] The actual process undergone in domesticating the wolf is still debated. Although it is popularly assumed that dogs originated as a result of artificial selection, the general intractability of adult wolves to human handling has led certain experts to theorise that the domestication process occurred through natural selection, when Mesolithic human communities began building permanent settlements in which a new ecological niche (middens and landfills) was opened to wolves. These wolves would have formed a commensal relationship with humans, feeding on their waste over many generations, with natural selection favouring assertive wolves with shorter flight distances in human presence, and causing physical changes related to the redundancy of features adapted for hunting big game.[41]
Although dogs are the wolf's closest relative (the genetic divergence between gray wolves and dogs is only 1.8%, as opposed to over 4% between gray wolves, Ethiopian wolves andcoyotes),[42] comparative studies on dog and wolf behaviour and anatomy have shown that dog physiology and most dog behaviours are comparable to those of young wolves, an example ofneoteny and pedomorphism.[43] The tympanic bullae are large, convex and almost spherical in wolves, while the bullae of dogs are smaller, compressed and slightly crumpled.[44] Compared to equally sized dogs, wolves tend to have 20% larger skulls and 10% bigger brains.[45] This reduction lies in the parts of the brain that deal with sense impressions.[46] The teeth of wolves are also proportionately larger than those of dogs; premolars and molars of wolves are much less crowded, and have more complex cusp patterns.[47] Dogs lack a functioning pre-caudal gland, and most enter estrus twice yearly, unlike wolves which only do so once annually.[40]
Hybridization
See also: Canid hybrids
Hybridization with dogs
Main articles: Wolfdog and black wolf
Although dogs and wolves are genetically very close, and have shared vast portions of their ranges for millennia, the two generally do not voluntarily interbreed in the wild,[40] though lone wolvesmay fraternise with guard or herding dogs as surrogate pack members.[48] They can produce viable offspring, with all subsequent generations being fertile.[40] In North America, black colored wolves acquired their coloration from wolf-dog hybridization, which occurred 10,000–15,000 years ago.[49] Although wolf-dog hybridisation in Europe has raised concern among conservation groups fearing for the wolf's purity, an analysis on the mtDNA sequences show that introgression of dog genes into European wolf populations does not pose a significant threat. Also, as wolf and dog mating seasons do not fully coincide, the likelihood of wild wolves and dogs mating and producing surviving offspring is small.[50] Like pure wolves, hybrids breed annually, though their mating season occurs three months earlier, with pups mostly being born in the winter period, thus lessening their chances of survival.[40]
Although it is popularly believed that some Inuit tribes mate their sled dogs to wolves in order to improve their stamina, this is probably untrue, as wolf hybrids are generally unable to cooperate effectively in pulling harnesses, and their stamina is much less than that of sled dogs.[51] The captive breeding of wolf-dog hybrids has proliferated in the USA, with 300,000 such animals being present there.[40] The most commonly used dog breeds for this purpose are of the spitz group.[52] At least two wolf-dog breeds have been created in Europe, the Saarlooswolfhond and theCzechoslovakian Wolfdog, both by crossing wolves with German shepherds.[52]
Hybridization with coyotes and golden jackals
Numerous genetic studies indicate that North American gray wolves have hybridized with coyotes in varying degrees in different areas. Studies on mtDNA and microsatellite loci indicate that wolves have hybridized extensively with coyotes in the northeastern USA and southeastern Canada, with the frequency of coyote haplotypes in wolves tending to increase to the east, from 50% in Minnesota, to 100% in southern Quebec.[53] These hybrids called "coywolves" (or "coywolf" for singular) are smaller than wolves, and hold smaller territories, but are in turn larger and hold more extensive territories than coyotes.[54]
In 2011, an analysis of 48,000 SNP chips in the genomes of various wolf and coyote populations revealed that the eastern wolf (native to Algonquin Provincial Park) and the red wolf (native toNorth Carolina), both previously labeled as species distinct from the gray wolf, are in fact products of varying degrees of wolf-coyote hybridization. The wolf-coyote admixture resulting in the development of the eastern wolf may have occurred on the order of 600–900 years ago between gray wolves and a now extinct pre-Columbian coyote population. The eastern wolf has sincebackcrossed extensively with parent gray wolf populations. The red wolf may have originated later, approximately 287–430 years ago, when much of the southeastern USA was being converted to agriculture and predators were targeted for extermination. During this period, declining local wolf populations would have been forced to mate with coyotes, with the resulting hybrids backcrossing to coyotes as the wolves disappeared, to the extent that ~75–80% of the modern red wolf's genome is of coyote derivation.[32]
In an evolutionary biology research conducted by a team of researchers in the Uppsala University, analysis of control region haplotypes of the mitochondrial DNA and sex chromosomes from Mexican grey wolves, a critically endangered subspecies of the grey wolf once nearly driven to extinction in the wild, confirmed the presence of coyote markers in some of the wolves.[55] The study suggests that at some point in time, female coyotes in the south managed to interbreed with some of the male wolves of the remnant wild Mexican grey wolf populations with the female hybrids backcrossing with other male wolves. Analysis on the haplotype of some coyotes from Texas also detected the presence of male wolf introgression such as Y chromosomes from the grey wolves in the southern coyotes. In an extremely rare case, the study found that one coyote out of the seventy individuals from Texas was discovered to carry a mtDNA haplotype derived from a female Mexican grey wolf implicating that a male coyote had managed to breed with a female grey wolf in the wild. The Mexican grey wolves may be the only grey wolf subspecies in the southern States besides the domestic and feral dogs to have hybridized with coyotes.
Although hybridization between wolves and golden jackals has never been observed, evidence of such occurrences was discovered through mtDNA analysis on jackals in Senegal[26] and Bulgaria.[56]
Physical description
Anatomy
See also: Dog anatomy
The gray wolf is a slender, powerfully built animal with a large, deeply descending ribcage and a sloping back. Its abdomen is pulled in, and its neck heavily muscled. Its limbs are long and robust, with comparatively small paws.[57] The front paws have five toes each, while the back paws have four. The forelimbs are seemingly pressed into the chest, with the elbows pointed inward, and the feet outward, thus allowing both fore and hind limbs on the same side to swing in the same line. The wolf's legs are moderately longer than those of other canids. This enables the animal to move swiftly, and allows it to overcome the deep snow that covers most of its geographical range.[58] Females tend to have narrower muzzles and foreheads, thinner necks, slightly shorter legs and less massive shoulders than males.[59] Compared to its smaller 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.[26][44][60]
The gray wolf's head is large and heavy, with a wide forehead, strong jaws and a long, blunt muzzle. The ears are relatively small and triangular.[57] 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.[61][62] The canine teeth are robust and relatively short (26 mm).[44] The wolf can exert a crushing pressure of perhaps 1,500 lbf/in2 compared to 750 lbf/in2 for a German shepherd. This force is sufficient to break open most bones.[63] In cold climates, the 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.[64]
The gray wolf usually carries its head at the same level as the back, raising it only when alert.[57] 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,[65] 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.[66] A running wolf holds its head slightly low and cocked to one side, directing one ear forward and the other back. This posture allows the wolf to continually make use of its exceptional hearing.[67]
Dimensions
The gray wolf is the largest extant member of the Canidae, excepting certain large breeds of domestic dog.[44] Gray wolf weight and size can vary greatly worldwide, tending to increase proportionally with latitude as predicted by Bergmann's Rule,[68] with the large wolves of Alaska and Canada sometimes weighing 3–6 times more than their Middle Eastern and South Asiancousins.[69] On average, adult wolves measure 105–160 cm (41–63 in) in length and 80–85 cm (32–34 in) in shoulder height.[70] The tail is ⅔ the length of the head and body,[71] measuring 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 mm.[70] The skull averages 9–11 inches in length, and 5–6 inches wide.[72] 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).[5]Females in any given wolf population typically weigh 5–10 lbs less than males.[73]
Wolves weighing over 54 kg (120 lbs) are uncommon, though exceptionally large individuals have been recorded in Alaska, Canada,[73] and the former Soviet Union.[70][74] 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),[73] while the heaviest recorded wolf in Eurasia was killed after World War II in Kobeliaky, Poltavskij Region, Ukrainian SSR, and weighed 86 kilograms (190 lb).[74]
Fur
The gray wolf has very dense and fluffy winter fur, with short underfur and long, coarse guard hairs.[57] Most of the underfur and some of the guard hairs are shed in the spring and grow back in the autumn period.[5] The longest hairs occur on the back, particularly on the front quarters and neck. Especially long hairs are found 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.[75] 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.[5] In warm climates, the fur is coarser and scarcer than in northern wolves.[57] 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.[59] 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 110–130 mm.[76]
Coat colour ranges from almost pure white through various shades of blond, cream, and ochre to grays, browns, and blacks.[77] Variation in fur color tends to increase in higher latitudes.[78]Differences in coat colour between sexes are largely absent,[79] though females may have redder tones.[80] Fur color doesn't seem to serve any camouflage purpose, with some experts concluding that the blended colors have more to do with emphasizing certain gestures during interaction.[81] Black coloured wolves (which occur through wolf-dog hybridisation) rarely occur in Eurasia, where interactions with domestic dogs have been reduced over the past thousand years due to the depletion of wild wolf populations. Black specimens are more common in North America, with about half the wolves in Yellowstone National Park being black.[49]
Sensory abilities
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 sharper than that of the fox,[82] being able to hear up to a frequency of 26 kHz,[83] which is sufficient to register the fall of leaves in the autumn period.[82] The urban legend that wolves fear the sound of string instruments may have a basis in fact, as captive wolves have been shown to exhibit signs of intense distress when hearing low minor chords.[84] Its night vision exceeds that of other Canids.[82]
Behaviour
See also: Dog behavior
Social and territorial behaviors
Although some wolves are solitary, most are highly gregarious animals.[85] The basic social unit of a wolf pack is the mated pair, accompanied by the pair's adult offspring.[a] In ideal conditions, the mated pair produces pups every year, with such offspring typically staying in the pack for 10–54 months before dispersing.[9] The average pack consists of a family of 5–11 animals (1–2 adults, 3–6 juveniles and 1–3 yearlings),[87] or sometimes two or three such families,[85] with exceptionally large packs consisting of 42 wolves being known.[88] Triggers for dispersal include the onset of sexual maturity and competition within the pack for food.[89] The distance travelled by dispersing wolves varies widely - some stayed in the vicinity of the parental group, while other individuals have been recorded travelling great distances of 390 km, 206 km, and 670 km from their natal packs.[90] A new pack is usually founded by an unrelated male and female, travelling together in search of an area devoid of other hostile packs.[91] 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.[88] During times of ungulate abundance (migration, calving etc.), different wolf packs may temporarily join forces.[92]
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[93] or when the pups reach the age of 6 months, thus having the same nutritional needs as adults.[94] 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.[93] Prey density tends to be much higher in the territory's surrounding areas, though wolves tend to avoid hunting in the fringes of their territory unless desperate, due to the possibility of fatal encounters with neighboring packs.[95] 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.[94] Wolf packs are typically settled, and usually only leave their accustomed ranges during severe food shortages.[96]
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.[97][98][99][100][101] Scent marks are generally left every 240 metres throughout the territory on regular travelways and junctions. Such markers can last for 2–3 weeks,[94] and are typically placed near rocks, boulders, trees or the skeletons of large animals.[102] When scent marking and howling fail to deter strange wolf packs from entering another's territory, violent interactions can ensue.[94] 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.[103]
Reproduction and development
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See also: Canine reproduction and Animal sexual behavior#Canidae
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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.[104] If a dispersing male 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 wolves are termed "Casanovawolves" and, unlike males from established packs, they do not form pair bonds with the females they mate with. Some wolf packs may have multiple breeding females this way, as is the case in Yellowstone National Park.[105] 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. This behavior is common and is seen in many other animal species like the elephant.[106]
In addition to heterosexual behavior, homosexual behavior has been observed in wolves.[107] Male wolves often mount each other when the highest ranking female in the pack comes into heat.[108]
The age of first breeding in 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.[109] Estrus typically occurs in late winter, with older, multiparous females entering estrus 2–3 weeks earlier than younger females.[104] When receptive, the female averts the base of her tail to one side, exposing the vulva.[110] During mating, the male'sbulbus glandis expands, locking the pair into a copulatory tie[110][111][112] which may last 5–36 minutes.[112][113][114][115] Wolves are able to separate from a copulatory tie more readily than domestic dogs.[116] When a male wolf ejaculates, his final pelvic thrust may be slightly prolonged.[117] Ejaculation is induced by pelvic thrusting and undulation of the cervix. After the first ejaculation, the male lifts his leg over the female and faces the opposite direction. The male wolf usually ejaculates multiple times during copulation.[118] Because estrus in wolves lasts only a month, male wolves do not abandon their mates to find other females to inseminate as dogs do.
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.[119] Old females usuallywhelp 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.[120]Wolves bear relatively large pups in small litters compared to other canid species.[121] The average litter consists of 5–6 pups,[122][123] with litter sizes tending to increase in areas where prey is abundant,[122] though exceptionally large litters of 14–17 pups occur only 1% of the time.[123] Pups are usually born in spring, coinciding with a corresponding increase in prey populations.[119] 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.[121][124] 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.[7] By autumn, the pups are mature enough to accompany adults on hunts for large prey.[119]
Denning and sheltering behaviour
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.[125] Wolves do not line their denning places, a likely precaution against parasites.[126] The den is usually constructed not more than 500 metres away from a water source,[125] and typically faces southwards, thus ensuring enough sunlight exposure, keeping the denning area relatively snow free.[127] 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.[125]
Intelligence
See also: Dog intelligence
Although the wolf's intelligence has not been quantified, scattered reports[128] and laboratory studies[129] do give indications on the species' ability to remember, associate events, and learn. During the extermination of the American bison on the Great Plains, wolves learned to follow the sounds of gunshots, and would wait until the hunters had skinned and abandoned the bison carcasses before feeding on them. In northern Montana, where wolves were heavily persecuted by aerial hunters, wolves learned to avoid open areas whenever they heard aircraft. Conversely, biologists using aircraft to study wolves have managed to condition wolves not to fear their approach, even when flying low. When hunting, wolves tend to target the easiest options available to them: in areas populated by both moose and smaller deer species, the latter are taken in much higher proportion. The wolf's powers of memory were described by George Mivart, who reported that a tame wolf was able to recognise its master after a three-year absence.[128] Non-rabid wolves are able to distinguish between armed and unarmed people,[130] and typically avoid investigating people who display self-confident demeanors typical of being armed.[131] Adult wolves have been known to skillfully select hidden approaches when entering their dens, using bushes, wind-fallen trees, stumps, and other natural structures to conceal their approach.[130] Wolves with prior experience to traps may learn how to avoid or even harmlessly trigger them: in his hunt for the Currumpaw wolf, naturalist Ernest Thompson Seton noted that his initial attempts at capturing it were unsuccessful, as the wolf would dig up and spring the traps, or ignore them altogether.[132]
Though wolves are trainable, they lack the same degree of tractability seen in dogs. They are generally not as responsive as dogs are to coercive techniques involving fear, aversive stimuli and force. Generally, far more work is required to obtain the same degree of reliability seen in most dogs. Even then, once a certain behavior has been repeated several times, wolves may get bored and ignore subsequent commands. Wolves are more responsive toward positive conditioning and rewards,[133] though simple praise is not sufficient as in most dogs.[134] Unlike dogs, wolves tend to respond more to hand signals than voice.[134] Most attempts to train wolves as working dogs have met with failure. German biologist Erik Zimen attempted to train his captive wolves assled dogs, and although his wolves eventually accepted the harness and the need to pull the sled in a straight line, they were ultimately unreliable, as they fought for personal space, would ignore commands once tired, and were distracted by other wildlife.[135] However, John James Audubon recorded an instance of a wolf being trained to hunt deer in Kentucky,[136] and Henry Wharton Shoemaker published a similar account of settlers in western and central Pennsylvania using wolves as hunting dogs.[137] Buffon wrote in his Natural History of tamed wolves in Persiabeing trained to perform dances and tricks.[138]
Hunting and feeding behaviours
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.[139] A 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.[140]
- The stalk: The wolves attempt to conceal themselves as they approach.[141] 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.[142]
- 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.[143] If the targeted animal stands its ground, the wolves either ignore it, or try to intimidate it into running.[139]
- 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.[144] 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.[141]
- The chase: A continuation of the rush, the wolves attempt to catch up with their prey and kill it.[145] 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).[139] 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.[146]
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.[146] 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 imobilize it with their forepaws.[147] 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)[148] or during the denning period, when wolves require a ready supply of meat when denbound.[149]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.[147]Surplus killing may also occur when adult wolves are teaching their young to hunt.[150]
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.[151] 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.[152] 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 andstomach lining. The kidneys and spleen are eaten once they are exposed, followed by the muscles.[153] A single wolf can eat 15–19% of its body weight in a single feeding.[154]
Communication
See also: Dog communication
Visual
The gray wolf's expressive behavior is more complex than that of the coyote and golden jackal, as necessitated by its group living and hunting habits. While less gregarious canids generally possess simple repertoires of visual signals, wolves have more varied signals which subtly inter grade in intensity.[7][8] When neutral, the legs are not stiffened, the tail hangs down loosely, the face is smooth, the lips untensed, and the ears point in no particular direction.[155] Postural communication in wolves consists of a variety of facial expressions, tail positions and piloerection.[83] Aggressive, or self-assertive wolves are characterized by their slow and deliberate movements, high body posture and raisedhackles, while submissive ones carry their bodies low, sleeken their fur and lower their ears and tail.[156] When a breeding male encounters a subordinate family member, it may stare at it, standing erect and still with the tails horizontal to its spine.[157] Two forms of submissive behavior are recognized: 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.[158] When wolves are together, they commonly indulge in behaviors 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.[159]
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