Tucked in a hillside den, under a thick blanket of snow, a mother wolverine gave birth to two kits late on February 9, 2023. Or perhaps it was early February 10, for she “threw us for a loop,” Nolan Schlichter says. He’s the Assistant Curator of the Tropics Trail and Minnesota Trail Mammals, and a Zoo leader in wolverine care. He and his fellow keepers expected Zola, a 10-year-old wolverine, to give birth in one of multiple nesting boxes they had prepared for her in the behind-the-scenes, indoor portion of her habitat.

The outdoor den in the behind-the-scenes habitat of a breeding pair of wolverines at the Minnesota Zoo.

Instead, the kits were born white as the snow in a den outdoors. They were first spotted by zookeepers on an infrared camera, unmistakable against the dark brown fur of their mother. Zola’s behavior is true to her counterparts in the wild, Schlichter says. Female wolverines use natal (birthing) dens that are excavated in deep snow, which provides security for the newborns and buffers cold winter temperatures. “That’s what wolverines are geared for,” Schlichter says of this hardy mammal.

Welcoming Wolverines

After Zola moved the kits to an indoor den a few days later, staff were able to examine them by giving their mother a bone to keep her occupied.  The kits were healthy but helpless. Their eyes and ears were closed, as is typical of mustelids, the family of carnivorous mammals that includes wolverines, weasels, and otters. Staff determined there was one male kit, one female. They weighed 1.26 and 1.18 kg—but not for long. By their two-month checkup on April 11, they weighed double that. They received their first vaccinations from Dr. Anne Rivas, DVM, DACZM, the Zoo’s Director of Animal Health. Schlichter says vets and keepers work hand in hand—but they aren’t hand-rearing the kits.

“It’s best to let them be,” he says. “Their mom is incredibly protective of them. She knows what she’s doing.”

A wolverine kit is weighed during its two-month health checkup on April 11, 2023 at the Minnesota Zoo.

The kits are showing another sign of maturity: gray hair. They’re no longer snow-white, their characteristic masks are developing, and they’ll continue to darken in color over their first year of life. At the two-month mark, they’re “very close to mini-wolverines,” Schlichter says.

The kits will nurse for 70 to 80 days, when they become more interested in prey options than milk. They will spend up to a year with their mom. But by three months old, they’ll be bigger, bolder, and independently exploring the habitat away from her.

Breeding Success

 Wolverines (Gulo gulo) have two subspecies, the Eurasian (G. g. gulo) and North American (G. g. luscus). The Minnesota Zoo is the only zoo to have both subspecies. On the Medtronic Minnesota Trail, guests can visit “Cascade,” a male North American wolverine. A breeding pair of Eurasian wolverines, Zola and her mate Abisko, were brought to Minnesota from European zoos in an effort to maintain the genetic diversity of the species. Zola, Abisko, and the new kits are currently behind the scenes as the kits grow.

Schlichter notes the Minnesota Zoo and Northwest Trek Wildlife Park in Seattle are the “hubs of wolverine activity” on this continent.

“The Minnesota Zoo maintains AZA wolverine care in this country, and we look forward to continuing to do so,” Schlichter says. AZA is the Association of Zoos and Aquariums, which accredits more than 200 facilities, including the Minnesota Zoo, for meeting high standards of animal care and welfare.

A wolverine kit receives vaccinations and preventative medicine from veterinarians during its two-month health checkup on April 11, 2023.

Schlichter serves as the Wolverine Studbook Keeper for the AZA and is the liaison to and collaborates with the European Association of Zoos and Aquaria (EAZA) to conserve this species that is highly sensitive to deforestation, climate change, and human activity in its home mountain ranges.

The birth of two healthy wolverine kits here at the Minnesota Zoo contributes to “a record year going way back,” he says. “With seven kits born at three AZA zoos, this is the most successful year in a very long time.”

In part, that’s because wolverines are notoriously finicky breeders, he says.  He credits EAZA with finetuning care and breeding programs that “suit the wants and needs of wolverines.” Schlichter describes a lengthy process to get approved by EAZA to import a breeding pair. To start, the facilities must be in a northern climate with adequate cold temperatures and snowfall to signal to the female to implant her embryos.

And wolverines—known as relentless mammals with a “non-stop motor”—require a rugged environment.

“Wolverines climb and dig like no other animal,” Schlichter says. “They are incredibly powerful for their size and can excavate boulders and dig deep holes.”

It’s essential to have a large, secure habitat, like the Minnesota Zoo’s behind-the-scenes habitat dedicated to wolverine breeding. The IT/AV staff installed video cameras in the multiple den sites so keepers can monitor and zoom in on the mother without disturbing her. The Zoo’s expert carpentry and fabricating team built den boxes based on innovative EAZA designs.

“We’re one of the few zoos with those resources,” Schlichter says.

Contributing to Conservation

Thanks to technology staff who installed video cameras, Zookeepers can monitor the wolverine mother and kits in numerous den sites in the habitat.

 Based on the success of wolverines here in Minnesota and at other AZA zoos, Schlichter says more zoos are now interested in learning how to breed and conserve the species.

“I’m hoping over time we can continue to bolster and build a more sustainable studbook for wolverines,” he says.

Schlichter has the scoop on one other way the Minnesota Zoo’s wolverines contribute to conservation—with their scat. Keepers collect and send fecal samples from the pregnant female to researchers with Montana Fish, Wildlife & Parks. Our samples are tested against ones collected in the Montana mountains, which helps scientists determine if and how many wolverines are breeding in the wild. This data can indicate if populations are stable, increasing, or decreasing—and whether more efforts are needed for wolverines to survive and thrive.