How do you make Canadian wolves sterile?

Peggy Callahan crouches low to the ground, cups her mouth with her hands and howls.

The wolf pups sitting nearby instantly raise their heads, their ears alert to the haunting call.

They know that voice.

Callahan has been their main caretaker since the four Canadian pups first arrived in the spring at the Wildlife Science Center in Forest Lake.

They traveled all the way from British Columbia on a very special mission: to participate in a potentially groundbreaking study that researchers hope will reveal better ways to manage Canada's wolf population.

The study, the result of an unusual alliance between two countries, began when a Canadian veterinarian called the Wildlife Science Center and asked whether it would be willing to take the wolf pups.

In Canada, mountain caribou are dying and officials believe wolves are the culprit, said Callahan, a wildlife biologist and executive director of the center. As a result, Canadian officials are trying to protect the caribou by capturing wolf pups and euthanizing them, she said.

But now Canadian officials are exploring another option: sterilizing the wolves.

The Wildlife Science Center, a nationally known research and education facility that specializes in wolves and other predators, has teamed up with the Ministry of Environment of British Columbia and a top reproductive physiologist at the St. Louis Zoo to develop a way to sterilize the wolves from afar.

If all goes according to plan, new pups will come to the center every year and the study's sample size will grow. "It's a win-win," Callahan said. "The puppies don't get euthanized and the research gets done."

In May, a few people from the center drove 36 hours to Canada to pick up the wolf pups, which were only about 10 days old. On the drive home, the pups' eyes began to open, Callahan said.

For the first week or so, they needed to be bottle-fed around the clock. Callahan and her husband took the pups home every night to sleep, and volunteers and staff members took turns caring for them so they were never alone. "If you don't spend lots of time with them initially, they will be afraid of humans" Callahan said.

Researchers need to get close to the wolves to draw blood samples and conduct the reproductive studies. That wouldn't have been possible if the wolf pups were raised wild. So from the outset, the study partners made a conscious effort to "hand-raise" the wolves, Callahan said. That means they can never be released into the wild again. Instead, they'll stay at the center.

The pups aren't the only wolves at the center, which has an assortment of animals including owls, foxes, bears and about 50 wolves.

The Canadian pups started out eating a combined 20 cups of high-protein dog food a day. Each pup now weighs about 35 pounds, and their daily feedings include deer legs and geese in addition to the dog food.

"They're quite big for wolf puppies because of their good nutrition," Callahan said. "They're growing like mad." By the time they're full grown, they'll weigh 120 to 140 pounds each.

A 6-foot-high fence surrounds the large pen where the pups reside along with two local wolf pups the same age.

On a steamy afternoon last week, Callahan walked into the pen, accompanied by her black German shepherd, MaClein.

"Wanna see your pups?" Callahan asked MaClein, who jumped up and down excitedly and then darted toward the trees at the end of the pen where the pups were lounging.

The young wolves surrounded him and licked his mouth -- a submissive gesture, Callahan explained. MaClein and Callahan's other dog, Cassie, have adopted the pups and have become surrogate parents, she said.

A short while later, Callahan reentered the pen carrying a silver dish full of frozen mice -- treats! The pups came charging toward her and Callahan tossed the mice, one at a time, in their direction. "Vlad! You don't get them all," she yelled, chastising one of the larger pups. "You're going to get an ice cream headache!"

When the wolves are close to two years old, they will mature enough to reproduce, and then the researchers can try to develop a remote sterilization technique, Callahan said.

The hope is that if they can develop a drug-laced dart or something similar that can be administered from a distance, then the Canadians will be able to treat wolves in the wild to better manage the population. In the meantime, the four pups are contributing to another study. Their stool samples are being collected to determine whether they carry a parasite that is harmful to cattle.

Just how many more wolves will become a part of the reproductive management study, Callahan doesn't know. The Canadian officials are paying for a large enclosure to house all of the wolves in the study. They have not set a maximum number, and the only requirement right now is that there must be an equal number of female and male wolves.

"This is a long-term project," Callahan said.

Allie Shah • 651-298-1550