The gray wolf, grey wolf, or common wolf (Canis lupus) is the largest extant member of the dog family of mammals, the Canidae. Though once abundant over much of Eurasia, North Africa and North America, the gray wolf inhabits a reduced portion of its former range due to widespread destruction of its habitat, human encroachment, and the resulting human-wolf encounters that sparked broad extirpation. Although the species still faces some threats, it is relatively widespread with a stable population trend and has therefore been assessed as Least Concern by IUCN since 2004. Today, wolves are protected in some areas, hunted for sport in others, or may be subject to population control or extermination as threats to livestock, people, and pets. They occur primarily but not exclusively in wilderness and remote areas.
Although 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. 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. 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. If the targeted animal stands its ground, the wolves either ignore it, or try to intimidate it into running. 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. 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). Sometimes, a single wolf will distract the herd with its presence, acting as a decoy, while its pack mates attack from behind. 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, while Russian wolves will set up ambushes near water holes, sometimes using the same site repeatedly. 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.
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 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. When attacking moose, they occasionally bleed it to death by biting its soft nose. 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. Southern wolves may grab the animal by the neck and stun it by jerking its head downward, hitting its nose on the ground. 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) or during the denning period, when wolves require a ready supply of meat when denbound. 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. Surplus killing may also occur when adult wolves are teaching their young to hunt.