The grey wolf is one of approximately 35 species belonging to the family Canidae, which includes the coyote, jackal, fox, and the dog. This family is believed to have originated in North America 38 to 54 million years ago during the Eocene Epoch. Two species- and a varying number of subspecies- of wolves are recognized: the grey, or timber, wolf, once widely distributed in North America, Europe, and Asia; and the red wolf, which now occurs only in Texas and the south-eastern United States. An adult timber wolf measures up to 1.6m (6.5ft) in length, including the tail (which is less than half the body length), and may weigh up to 80kg (175lbs.). The animal is red- yellow or yellow- grey, with black patches above and white below: those in the far north, however, may be pure white, and black or. Brown timber wolves also occur. The red wolf is smaller in size and usually darker in colour. All wolves are characterized by powerful teeth, bushy tails, and round pupils, and they are distinguished from domestic dogs by certain characteristics of the skull.
Wolves are equally at home on prairies, in forestlands, and on all but the highest mountains. In the winter they travel in packs in search of food. Small animals and birds are the common prey of wolves, which also eat berries, but a pack may sometimes attack reindeer, sheep, and other large mammals, usually selecting weak, old, or very young animals for easier capture. When no prey can be found, wolves feed on carrion.
The den, of lair, of the wolf may be a cave, hollow tree trunk, a thicket, or a hole in the ground dug by the wolf. The breeding season is in the spring, and the female gas a litter of one to eleven cubs. Adults sometimes feed young cubs by regurgitating food for them. The cubs normally stay with the parents until the following winter but may remain much longer. Parents and young constitute a basic pack, which establishes and defends a territory marked by urine and feces, Larger packs may also assemble, particularly in the winter; the pack leader is called the alpha male, and its mate is the alpha female. As social animals, wolves exhibit behavioural patterns that clearly communicate dominance over or submission to one another; the communal howling of a pack may serve to assemble its members, communicate with other packs, advertise its territorial claims, or simply be a source of pleasure. Visual and olfactory communication signals are also important.
Although wolves are still abundant in Eastern Europe, Asia, Alaska and Canada. They are being diminished. The decreasing numbers of wolves are the result of encroachments on their territory by humans, who have long regarded wolves as competitors for prey and as dangerous animals as themselves. The fact is that few, if any, healthy wolves have attacked humans, whom they instead try to avoid, and wolves are valuable predators in the food web. Their decimation has led to the overpopulation of a number of other species in various areas. There are active efforts to reintroduce wolves to national parks in the United States, although such efforts are controversial.