Female wolves are only capable of mating and producing young once a year during their heat (oestrus) period, which lasts for only a few weeks. The breeding season for wolves is usually from February to March. However, some wolves mate as early as January, and in Northern Canada or Alaska, wolves may mate as late as April. Mating season occurs after winter so the wolf pups will have time to grow and develop before the next winter comes. Female wolves usually become sexually active at age two, although a female wolf may breed as early as age one. However, many female wolves don't mate until they are four or five years old.
The alpha female in a wolf pack is usually the mother of the pups. In almost all cases, the alpha male is the father of the pups, but in some instances the wolf who ranks just under the alpha wolf in the pack's hierarchy (the Beta wolf) will take over the alpha's role as father if the alpha wolf shows no interest in mating with the alpha female or any other pack member. Just before the breeding season, the male wolves (particularly the alpha male) in the pack will sniff, harass and pursue the alpha female. If needed, the alpha wolves may use physical force to prevent the other pack members from mating.
While most wolf packs produce only one litter of pups each year, biologists have observed packs that have had more than one litter, one of which was from a subservient female. Multiple litters often occur when the food supply is very adequate after a severe winter. Subservient females may also breed when the pack hierarchy is disturbed.
During their period of courtship, the alpha male and female will become very close to each other. They stay with each other almost all of the time, even while they are sleeping, and act quite affectionate towards each other. The alpha male and female have a strong relationship all year, but it becomes stronger as they prepare to mate. Once they are established as a breeding pair, they often stay together for life, although infrequent changes in partners may occur. It is untrue that wolves always mate for life, though wolves typically only have one mate at a time. Serial monogamy is not uncommon, whereas polygamy is rare. The male and female often mate several times before the female's heat period is over.
A few weeks before the pups are born, the female will select a den. Most often, the den is a burrow dug into a soft area of a hillside. The den generally consists of a tunnel with an opening just large enough for an adult wolf to enter that leads to an enlarged chamber where the pups will be born. A rock cave, a large, hollow log, an old beaver lodge or an abandoned fox den may also serve as a den. Female wolves have also given birth in a depression right on the ground. Wolves often reuse dens, but will change dens if their current one becomes severely infested by parasites or is disturbed by other animals.
The alpha male will become very protective of the den and will lead predators away from it but may run if humans approach. While the female is preparing the den, the alpha wolf (and perhaps other wolves) often start to store meat in a cache near the den.
The gestation period for a wolf is 63 days, as it is for a domestic dog. The female wolf will usually give birth (alone) to a litter of 5 or 6 pups, although some litters are as small as two or as large as 11. The female will not allow the male into the den while she is giving birth. The female must immediately bite off each pup's umbilical cord and she must break and remove the amniotic sack that surrounded each pup. She will then guide them to her nipples and they will instinctively start to suck. Each pup is born blind and deaf and unable maintain their own body temperatures. The average weight of a new-born wolf pup is 0.5 kilograms (one pound). The mother wolf will stay with her pups almost all of the time at this stage but will leave the den to eat the food the other pack members will leave outside for her. A wolf den is usually near a river or lake so the mother wolf does not have to go far to get water.
At the end of two weeks the pups will have opened their eyes and will start to develop their milk teeth. They will also be able to walk on all four of their legs and will weigh about 3.2 kilograms (7 pounds). When the pups are three weeks old they will be able to see and hear and the mother will start to regurgitate solid food for them to eat. Wolf pups are born with blue eyes, which usually change to a yellow-gold or orange colour by the time the pups are 8-16 weeks old. When the pups are about one month old they will leave the den. When they leave the den they will be greeted by the other members of their pack very enthusiastically.
When they are able to leave the den, the pups become the responsibility of the whole pack. Each wolf in the pack will protect the pups, and will watch out for possible predators (such as eagles or bears) that may attack the pups. Members of the pack besides the mother will start to regurgitate food for the pups. The pups spend much of their time playing by chasing and wrestling with each other. They will constantly try the patience of the older wolves by nipping at their ears and tails and by pouncing on them. Adult wolves are very patient with the pups and will only reprimand them by bearing their teeth if the play becomes too rough. The pups are treated with a great deal of affection by all members of the pack, and since each pack will typically have only one litter (there are rare exceptions to this), they are viewed as "communal babies".
While the pups are out of the den, but are still too young to hunt, they will stay at a "rendezvous" site with a pupsitter (one of the subordinate wolves). Wolf pups are moved to a rendezvous site when they are about 5 to 8 weeks old. The rendezvous site will have an area of about 1000 square meters (1200 square yards) and it serves as a meeting place for the adult wolves and as a home for the pups until they can go on hunts. The pups will gradually learn about their pack's hierarchy and their own place within it.
As the pups mature, they will be introduced to potential prey, different scents and trails, and hunting strategies. Wolf pups start to accompany adults on hunting trips when they are 12 weeks old. The pups will start to explore their surroundings on their own, and at age 7-8 months, they will start to actively hunt with the pack. Some pups will eventually leave their pack and will become lone wolves (dispersers). Lone wolves are often at great risk of being attacked or killed by other wolves whose territory they have intruded on. If a lone wolf finds a mate and establishes a territory, it will be the founder of a new pack. Some wolves will stay with their pack (biders) and will wait for an opportunity to move up in its hierarchy when the alpha wolf dies or becomes sick and old. About half of the wolf pups born each year will die before their first year. Disease, hunting accidents, attacks by bears, fights or inexperience are often to blame.