Photo Credit: Jason Hahn
Photo Credit: Andrew Perry
Wolves give birth to puppies only once a year, producing average litter sizes of five or six, although nine or eleven puppies have been recorded. Newborn pups weigh about a pound each and are blind and deaf. They're unable to maintain their body heat independently so rely on their mother for warmth until about three weeks of age. Despite this, they're very strong and muscular, crawling and competing with litter mates for their mother's milk. They generally nurse four to five times a day for periods ranging from about three to five minutes each.
Since their mother is more or less restricted to the den when the pups are so young, she relies on the other wolves in her pack to bring her portions of food from the hunt or to return from the hunt and regurgitate food for her. The puppies' eyes are fully open by about two weeks of age and they're able to hear by about three weeks old. About this time their milk teeth break through their gums and they start eating regurgitated food and small pieces of meat delivered from the hunt.
As wolf pups develop, they eat greater amounts of solid food, either brought back to them from the hunt or regurgitated for them by the adults when they return to the den. Pups madly rush any arriving adult, swarming around, excitedly licking and jumping at its mouth, encouraging regurgitation of its partially digested food. An adult can regurgitate at least three times from any one stomach load and probably still have some food left for itself. As pups get older, their food-begging behavior eventually transforms into a greeting ritual by adult wolves towards the pack leaders.
Pups grow quickly and by only five or six weeks of age, are robust enough to follow the adults as far as about a mile from the den. While a single pup may be weaned as early as six weeks of age, a full litter is weaned when about three weeks older. At about eight or nine weeks old the pups generally forsake the den and are moved to a "rendezvous" site which is essentially a den above ground.
In forested areas, rendezvous sites are often situated in low, shaded areas. The pups spend a lot of time huddled together in a pile in one part of the site, traveling back and forth a few hundred yards around it. They remain there while the adults are off hunting. In open areas, pups are kept in willow thickets, around rock piles or near holes in the ground. In the photo at right, the black wolf pup has already begun to lose his fat, round puppy look. It'll soon be replaced by the gangly, adolescent appearance of the wolf pups in the photo below. Wolf puppies' legs lengthen quickly and the furry baby hair is replaced by the coarser coat of an adult wolf.
Wolf pups are whelped in the spring by the pack's alpha female after a gestation period of about 63 days. This is the only time of year the alpha female uses a den and also the only time the rest of her pack remains close to one.
Dens are often a hole in the ground but can be a rock cave or crevice as well. About three weeks before whelping, the alpha female either digs the den or claims a den previously used by a smaller animal such as a coyote or fox. Often aided by lower ranking females within her pack, she creates or remodels shelter for her soon to be born puppies. Old beaver lodges and hollow logs sometimes provide wolves with perfect denning areas.
In rarer instances, wolves give birth to their pups on top of the ground with no shelter at all. Wolf biologist David Mech recounts four such cases. In one, all the puppies died. In two others, the female later moved them to a better location. In the last instance, the puppies' fate remains unknown. The photo below, from David Mech's The Way Of The Wolf, is of an Arctic female's den that is merely a shallow pit in the ground. Biologists don't fully understand why wolves use pits as dens, but some suggest these sites are used only by inexperienced females. There is at least one record however, of an experienced female using a pit for her second litter.
Sometimes, if the adults kill a large animal, they take the pups to it rather than carrying back food to the rendezvous site. As the pups hang around the carcass, they essentially develop a rendezvous site right at the kill. Some wolf packs use the same rendezvous site throughout summer. Others move the pups to a series of sites, some of them often many miles from the others. Pups adapt well to travel since they begin taking on the conformation of adults when they're only about eight weeks old. At this age they start growing adult hair around their noses and eyes and they weigh between 15 and 20 pounds.
Pups remain at rendezvous sites until about mid-September, when they begin traveling with the pack more often. "Runt" pups often stay at the rendezvous site for several more weeks. Although the adults continue to return to the site with food, they do so less often since they're traveling further away with the healthier pups. The runts either die or manage to gain enough weight to join the traveling pack. In The Way Of The Wolf, Mech writes, "This is a no-nonsense system of reproduction that forges strong, competent animals. Life is generally rough for wolves, so there is little room for individuals that cannot make it. The survivors then are the best prepared for contending with the formidable challenges they must face."
Photo Credit: Denver Bryan
Most often, typical wolf dens are dug underground, usually into a hillside near a water source such as a river or stream. Den entrances usually measure anywhere from fourteen to twenty-five inches in diameter and are usually oval shaped. The tunnel, which generally extends from six to fourteen feet into the earth, may be the same diameter as the entrance but sometimes it's larger. The newborn puppies are kept in an enlarged chamber at the end of the tunnel. No bedding is used. Each den may have several entrances and passageways. A large mound of soil from the excavation marks the main entrance.
Adolph Murie crawled inside a wolf den in Mount McKinley Park in Alaska. He wrote, "I wriggled into the burrow which was 16 inches high and 25 inches wide. Six feet from the entrance of the burrow there was a right angle turn. At the turn there was a hollow, rounded and worn, which obviously was a bed much used by an adult...From the turn the burrow slanted slightly upward for 6 feet to the chamber in which the pups were huddled and squirming."
Dens are often re-used from year to year, especially where good den sites are scarce. A den studied by Adolph Murie in Denali National Park in the early 1940s is still being used regularly today. In the High Arctic, David Mech discovered a den that was a spacious cave. The area surrounding the den was littered with fresh, moderately old and very old bones of prey that the adults had brought back for pups from the hunt. When two of the old bones were tested by radiocarbon technique, they were shown to be 232 and 783 years old. That particular den had been used by wolves over a period of almost 800 years.
The pups first show up outside of the den at three or four weeks of age. By four weeks old, their ears stand erect and they spend more and more time outside the den - until a sudden sound or frightening noise sends them scurrying to safety back inside. At this age, their mother leaves them for hours to hunt. They're not alone however, being left in the care of a "babysitter" wolf, usually an aunt or older sibling. There are exceptions however. David Mech observed one mother wolf who stayed away from her lone four-to-five-week-old pup for twenty hours at a time. Since other pack members were absent as well, "Every few hours, the lonely little fuzzball would wander to the front of the den and let out plaintive, pleading pup-howls advertising its empty belly." When pups are very young, their high vocalizations sound a little like those made by coyotes.