Studies of Wolf Denning Behavior in Yellowstone, progress report 1998

Linda Thurston, M.S. candidate at Texas A & M University

The Yellowstone Wolf Project has conducted a wolf denning study for the past three years, since the first naturally formed pack reproduced in the park. The study has two objectives, (1) to collect information that is pertinent to monitoring and management of this endangered species, and (2) to gather behavioral observations which will give a better understanding of the species. The original focus of den study was to provide wolf reproduction and pup survivorship information necessary to remove wolves from endangered species status. However, in Yellowstone we have one of the first opportunities to obtain behavioral observations of wild wolves. Most studies on wolf behavior were done on captive wolves, but because wolves in the wild are able to travel up to 40 miles a day, confinement can alter the behavior of these mobile, highly social animals. The Yellowstone Wolf Project has taken advantage of this opportunity by collecting behavioral data in the course of other den study directives.

Den study begins in early April with a crew of volunteers that will monitor chosen packs for four months. The crew’s initial objective is to follow packs with radio tracking equipment to determine when the breeding females whelp (give birth to) pups. Since we are able to observe some wolves breeding, the whelp dates of those females can be estimated based on a 63-day gestation period. Otherwise, it becomes apparent when the female, previously traveling widely with her pack, does not leave the vicinity of a den for a month. The packs which are monitored are selected on the basis of accessibility in the spring—the Rose Creek, Druid Peak, Leopold, and Chief Joseph Packs have fit the bill. Snow depth prevents data gathering on packs in the park’s interior, except by weekly aerial surveys.

During 1998, the Rose Creek Pack was the first pack to have pups, with two females both whelping on or around April 7th and sharing the same den. The other three packs had their litters in the following two weeks. Once the packs have had their litters, a team assigned to each pack monitors the den for 48 continuous hours once a week for about three months. So their presence is not known to the wolves, observers are stationed approximately a mile from the den. They obtain radio telemetry locations and opportunistically observe wolf behavior using high-powered field scopes.

The study lasts until the pups of each of the four monitored packs are 15 weeks old, or until the packs become inaccessible by moving to higher elevations. Duration of the study coincides with the weaning schedule of the pups: they begin to be weaned at approximately 5 weeks of age and are fully weaned by 10 weeks. A comparison of parental effort through 3 phases of pup development can then be made with the hunting demands on the pack theoretically increasing with each phase.

The criteria to remove wolves from the endangered species list are 10 breeding pairs reproducing successfully for three successive years in three recovery areas: northern Montana, central Idaho, and Yellowstone. By revealing factors affecting denning ecology, the study has provided insight to the conditions under which packs are able to successfully raise litters. Key information includes the date pups are born, initial litter size, and causes of pup mortality.

During 1998 the Rose Creek Pack had 11 pups between two females but one pup died during the first month of age. Possible causes of pup mortality include disease, predation, malnutrition, and territorial intrusions by neighboring packs. The cause of the Rose Creek Pack pup mortality is unknown, nevertheless the pack had high pup survivorship with the remaining 10 still believed to be alive. If, for example, packs were to loose many pups at approximately one month of age, canine parvovirus would be suspected and managers could then decide what action needed to be taken, if any.

Other management-oriented information includes the nutritional condition of pups. The majority of pups observed in Yellowstone have been vigorous and playful, an indication of good nutrition. If the available prey base were to fluctuate in the future making less prey available to wolves, we might see more lethargic pups and lower survivorship.

Data on disturbances at the den site may be valuable in Yellowstone Park. Some wolf dens are within management closures in the park, particularly when packs have selected dens near roads. This has enticed visitors to approach the den or interfere with pack movements to and from the den. Detailed notes have been taken on these human-caused disturbances and the resulting wolf behavior. One case of a wolf moving her den due to human intrusion has been documented.

While gathering information that may influence management decisions, we are also able to gather information that addresses theoretical questions. New information of this nature could influence future wolf management, but it is more to understand how the species responds to its environment. For example, if a lone female can successfully raise a litter of pups without the food and protection afforded by other pack members, then why do wolves live in packs? While a rare occurrence, single mothers have been nominally successful. In 1997 and 1998, Number16 of the Chief Joseph II Pack was able to raise pups without help from other wolves. But because Number 16’s 1997 litter did not fare well, it appears that pup survivorship is enhanced when helper wolves are available.

We are also collecting information on the amount of time each pack member stays at the den and the activities they are engaged in while in attendance. When possible, we are recording the activities of wolves while away from the den as well. Over time, we will hopefully be able to gain insight as to how the subordinate members of the pack contribute to, or detract from, raising the pups. Are the subordinates providing care to pups in the way of bringing food, providing protection, and playing the role of babysitter while the mother is away? Or are some wolves merely near the den to intercept food brought back by other wolves? Behaviors on both sides of these questions have been observed. How does the amount and type of care provided to pups differ between males and females within the same pack and among different packs? How much does this pup care vary depending upon pack size and social composition? Preliminary findings to these questions are being analyzed and will be presented in my graduate dissertation. While the methods of the study will be refined with time, the Yellowstone Wolf Project is dedicated to continuing data collection on wolf denning behavior well into the future. It is only by collecting information over a long period that we will begin to see trends, and develop a better understanding of the denning ecology of wolves in the wild. L.T.


If you would like to make a donation to support the wolf denning study, make a contribution to the Wolfstock Foundation


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