This essay was provided by Jeremy Heft, Biologist and Sanctuary Manager, Wolf Education and Research Center.
WOLF BEHAVIOR 101
LESSON 12: DEN BEHAVIOR AND SELECTION
As the snow melts in the spring, all gray wolf packs begin preparation for one the most exciting times of the year—the birth of puppies. As discussed in previous lessons, breeding season for wolves begins in December and usually terminates in early March, with the actual mating occurring typically in late February.
Wolves have a 63 day gestation, which means puppies are born in April or May. This annual event is perfectly timed so puppies are not subjected to the extreme cold of winter immediately upon birth, plus most other Northern hemisphere mammals are birthing at the same time. This is not a coincidence, but rather an evolved pattern so the pack has ample prey in the form of elk or deer fawns, which means more food to share with the new puppies.
Another benefit of the spring season is the ground is quite soft due to being saturated from snow melt, thus is easy to dig into. Packs create a den for the mother to birth her puppies in, and then the pups and the mother reside in this den for the first several weeks after birth. The mother stays with the pups while the pack hunts, or a “pupsitter” is appointed by the pack to watch over the puppies when the mother must leave. Either way, the puppies remain in or near the den for the first few months of their life.
After the puppies are too large to inhabit the den, they are moved to a rendezvous site, where they stay while the pack is away hunting. Now considered sub-adults, the wolves will never use a den again in their life, unless one of them later becomes a mother herself. Dens are only used for birthing puppies, not as a sleeping area or to escape the weather as you may think. In captivity, wolves will occasionally use dens to escape dominance from other members, but this is not a natural behavior, rather an ingenious way to use the available environment to cope with the negative aspects of captivity.
In 2004, WERC supported an interesting Masters Thesis study by Jon Trapp of Prescott College. Jon, a WERC supporter and personal friend, examined wolf den selection and characteristics in the Northern Rocky Mountains. The study showed that nearly all dens existed within the core area of the pack’s territory, or the area used most frequently by the pack. The most important factors in selection of a den site were determined to be adequate canopy (or large tree) cover, herbaceous vegetation nearby, small logs and rocks near the site, and the proximity to a water source (usually within 100 m).
Jon found that many dens were visually obscured from a close range by vegetation, making the dens difficult to locate. This is probably important for protection of the puppies from predators and maybe even humans. The study also found that human made structures such as roads were not a significant factor in choosing den sites, therefore providing more proof that wolves can probably coexist closely with human society. Most dens were dug under a fallen tree root system or under a rock or similar large item, probably to help support the roof of the den.
The soil type of the den site was deemed important, as most dens possessed a sandy-type soil that allowed easy drainage thus preventing the den from being flooded. Jon’s findings were important to wolf protection, as managers now have better knowledge of potential den areas so protection from humans can be accomplished by closing certain high potential den areas to human activity during the birthing season. This would allow packs to birth and care for their puppies undisturbed, leading to healthier wolf populations in the future.
WERC is proud to have been a part of this important study.