Gray Wolf
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[Photo] Gray wolf. Source U.S. Fish & Wildlife Service. Date January 29, 2002. Author John and Karen Hollingsworth

The Gray Wolf (Canis lupus; also spelled Grey Wolf, see spelling differences; also known as Timber Wolf or Wolf) is a mammal in the order Carnivora. The Gray Wolf shares a common ancestry with the domestic dog (Canis lupus familiaris), as evidenced by DNA sequencing and genetic drift studies. Gray wolves were once abundant and distributed over much of North America, Eurasia, and the Middle East. Today, for a variety of human-related reasons including widespread habitat destruction and excessive hunting, wolves inhabit only a very limited portion of their former range.

The Gray Wolf, being a keystone predator, is an integral component of the ecosystems to which it typically belongs. The wide range of habitats in which wolves can thrive reflects their adaptability as a species, and includes temperate forests, mountains, tundra, taiga, and grasslands. In the much of the world, with the exception of Northern regions, they are listed as endangered. They continue to be hunted in many areas of the world as perceived threats to livestock and humans, as well as for sport.

Anatomy, physiology, and reproduction

Features and adaptations
Wolf weight and size can vary greatly worldwide, though both tend to increase proportionally with higher latitudes. Generally speaking, height varies from 0.6???0.8 meters (26???32 inches) at the shoulder, and weight can range anywhere from 23???59 kilograms (50???130 pounds), making wolves the largest among all wild canids. Although rarely encountered, extreme specimens reaching over 77 kg (170 lb) have been recorded in Alaska and Canada, and the heaviest wolf on record, which was killed in Alaska in 1939, weighed 80 kg (175 lb). The smallest wolves come from the Arabian Wolf subspecies, the females of which may weigh as little as 10 kg (22 lb) at maturity. Customarily, however, wolves will be of a more typical physical capacity, with the females in a given population weighing about 20% less than their male counterparts. Wolves can measure anywhere from 1.3???2 meters (4.5???6.5 feet) from nose to tail tip, with the tail itself consisting of approximately one quarter of overall body length.

Wolves are built for stamina, possessing features tailored for long-distance travel. Narrow chests and powerful backs and legs contribute to the wolf's proficiency for efficient locomotion. They are capable of covering several miles trotting at about a 10 km/h (6 mph) pace, though they have been known to reach speeds approaching 65 km/h (40 mph) during a chase (wolves only run fast when testing potential prey). While sprinting thus, wolves can cover up to 5 meters (16 ft) per bound.

Wolf paws are able to traverse easily through a wide variety of terrains, especially snow. There is a slight webbing between each toe, which allows wolves to move over snow more easily than comparatively hampered prey. Wolves are digitigrade, so the relative largeness of their feet helps to better distribute their weight on snowy surfaces. The front paws are larger than the hind paws, and feature a fifth digit, a dewclaw, that is absent on hind paws. Bristled hairs and blunt claws enhance grip on slippery surfaces, and special blood vessels keep paw pads from freezing. Furthermore, scent glands located between a wolf's toes leave trace chemical markers behind, thereby helping the wolf to effectively navigate over large expanses while concurrently keeping others informed of its whereabouts.

A wolf sometimes seems more massive than it actually is due to its bulky coat, which is made of two layers. The first layer consists of tough guard hairs designed to repel water and dirt. The second is a dense, water-resistant undercoat that insulates. 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.

Coloration varies greatly, and runs 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 certainly 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.

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

Wolves have stout, blocky muzzles that help distinguish them from coyotes and dogs. Wolves also differ in certain skull dimensions, having a smaller orbital angle, for example, than dogs (>53 degrees for dogs compared to <45 degrees for wolves) while possessing a comparatively larger brain capacity. Larger paw size, yellow eyes, longer legs, and bigger teeth further distinguish adult wolves from other canids, particularly 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. 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 are designed to hold and subdue the prey. Powered by 1500 lb/sq. inch of pressure, a wolf's teeth are its main weapons as well as its primary tools. Therefore, any injury to the jaw line or teeth could devastate an individual, dooming it to starvation or incompetence.

Courtship and mating
Usually, the instinct to pass on genetic material 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 who reached sexual maturity during the previous breeding season. It takes two such dispersals from two different packs for the process to take place, as dispersing wolves from the same maternal pack tend not to mate. Once two dispersing wolves meet and begin traveling together, they immediately begin the process of seeking out territory, preferentially doing so in time for the next mating season. The bond that forms between such wolves often lasts for the shorter of the two lifetimes, with few exceptions.

During the mating season, breeding wolves become extremely affectionate with one another in anticipation for the female's ovulation cycle. Overall, pack tension rises, as each mature wolf begins to feel the urge to mate. In fact, during this time, the alpha male and alpha female may be forced to aggressively prevent other wolves from mating with each other. Under normal circumstances, a pack can only support one litter per year, so this type of dominance behavior is beneficial in the long run.

When the alpha female goes into estrus???a phenomenon that occurs once per year and lasts 5???14 days,???she and her mate will spend an increased amount of time in seclusion. Pheromones in the female's urine and the swelling of her vulva let the male know when his mate is in heat. She will be unreceptive for the first few days of estrus, during which time she sheds the lining of her uterus. Once the female begins to ovulate, mating occurs.

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???30 minutes, during which period the male will ejaculate multiple times. 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 ordeal is repeated many times throughout the female's brief ovulation period, which occurs once per year per female, unlike female dogs, with whom estrus usually occurs twice per year.

Breeding and life cycle
Normally, only the alpha pair of the pack breeds, which is a kind of organization not uncommon to other pack-hunting canids including the Dhole and the African Hunting Dog. Mating occurs between January and April, happening later in the year as latitude increases. A pack usually produces a single litter, though sometimes multiple litters will be born if the alpha male mates with one or more subordinate females. Under normal circumstances, the alpha female will try to prevent this by aggressively dominating other females and physically separating them from the alpha male during the mating season.

The gestation period lasts 60???63 days, and at the weight of 0.5 kg (1 lb), the pups are born blind, deaf, and completely dependent on their mother. There are 1???14 pups per litter, with the average litter size being about 4???6. Pups reside in the den, where they are born deaf with their eyes closed, and stay there until they reach about 3 weeks of age. 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. 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. They begin eating regurgitated foods after 2 weeks??? by which time their milk teeth have emerged??? and are fully weaned by 8???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.

After 2 months, the restless pups will be moved to a rendezvous site, which gives them a safe place to reside while most of the adults go out to hunt. An adult or two will 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 (they tag along as observers until about 8 months, by which time they are large enough to actively participate), and will receive first 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.

Wolves typically reach sexual maturity after 2 or 3 years, at which point many of them will feel compelled to leave their birth packs and search out mates and territories of their own. Wolves that reach maturity generally live 6???8 years in the wild, although in captivity they can live to be twice that age. High mortality rates result in a relatively low life expectancy for wolves on an overall basis. Pups die when food is scarce; they can also fall prey to other predators such as bears, or, less likely, coyotes, foxes, or other wolves. The most significant mortality factors for grown wolves are hunting and poaching by humans, car accidents, and wounds suffered while hunting prey. Wolves are susceptible to the same infections that affect domestic dogs, such as mange, heartworm, rabies and canine distemper, and such diseases can become epidemic, drastically reducing the wolf population in an area.

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