Researchers visit wolf dens to learn more about pup survival and wolf population dynamics
From somewhere in the dark recesses of the den came nearly inaudible squeaks and whimpers. Carolin Humpal, a wildlife research biologist for the Minnesota Department of Natural Resources, had already peeked inside. She knew what she would find once she slithered head-first down the entry hole and into the den.
A pile of wolf pups. Maybe two weeks old. Five of them.
Humpal and a team of other wildlife biologists had come to examine the pups and place a trail camera outside their den. The research is part of a state and tribal effort to better understand the dynamics of Minnesota’s wolf population.
“It’s a component of our broader wolf monitoring,” said the DNR’s John Erb, a wolf research biologist based at Grand Rapids. “The pup part of it is kind of a pilot project. We’re trying to get some experience with locating dens, and we’re looking at options for monitoring dens and counting pups.”
The work eventually will help wolf researchers monitor pup survival and learn more about what factors influence that survival, Erb said. Minnesota’s wolf population was estimated at about 2,221 in 2015, according to the DNR.
This den was just west of Cloquet on land owned by the Fond du Lac Band of Lake Superior Chippewa. The Band’s Resource Management Division is working with the DNR on wolf research. Along with Humpal on this mission to find wolf pups on a mid-April afternoon were DNR wolf research biologist Barry Sampson; Mike Schrage, wildlife biologist for the Fond du Lac Band; and Terry Perrault, a technician for the Band’s Resource Management Division.
Tough to find
Just finding the den was a challenge. It had taken five of us, walking abreast at intervals through the woods, nearly an hour to locate the den. Working from mapped GPS-tracking movements of a radio-collared adult wolf in this pack — though not the pups’ mother — Schrage had led us to this patch of woods. We were looking for a hole in the ground with freshly excavated dirt all around.
“Found it!” Sampson called out finally.
He and Humpal assumed the female wolf that had given birth to these pups was somewhere not far away, observing our visit and waiting for us to leave.
The pups’ mother is part of a pack estimated at five wolves in all, Schrage said. The den site is in an area near homes, small farms and and paved roads. Yet the wolves go mostly unnoticed.
“They’ve probably been there for years,” Schrage said, “and yet mostly they stay out of sight and conflict with people.”
Entering the den
Now it was time to go to work. Humpal scooched down the entry hole until only her lower legs and boots remained outside. Later, she described the five pups she saw.
“They were all piled together,” she said. “It was still fairly chilly, so they have to be huddled up together to share body heat.”
The pups’ eyes were open, indicating they probably were a couple of weeks old, Sampson said. Although they moved away from Humpal a bit, she said the plump little furballs didn’t struggle as she picked them up one at a time and handed them out to Sampson.
He checked their physical condition and determined whether they were males or females.
Perrault eased the pups into soft flannel bags. He weighed them quickly — about 3½ pounds each. Schrage recorded the pups’ weights and genders — four male, one female. One by one, the pups went back to Sampson and then to the waiting hand of Humpal, who still was mostly inside the den. Each pup was back in the den within less than a minute.
“Nice belly,” Sampson said, inspecting the plump tummy of one pup before it went back to Humpal.
The biologists performed their tasks quickly and in hushed voices. These intrusions at dens are kept to a minimum, Sampson explained, to disturb the wolves as little as possible. All of us wore rain gear to minimize our scent, and we had been sprayed with a scent-masking compound. Everyone wore latex gloves.
In less than 15 minutes, with all work completed and a trail camera hung on a nearby tree, the biologists left the site. Sampson had smoothed the dirt at the edge of the den. The pups were all in a heap again.
Their mother was never seen.
The value of research
So far, researchers have visited and inspected pups at a dozen to 15 dens in the past three or four years, the DNR’s Erb said. Pup counts and pup survival are not a necessary component of the DNR’s wolf population estimates, he said. But tracking birth and death rates, as DNR researchers do for some other species, could help the agency develop better population models, he said.
In addition, better understanding of wolf pup survival could help researchers relate that information to other wolf population factors such as prey density or the presence of parvovirus, Erb said.
Following our visit to the den site, it was difficult to know what effect the intrusion would have on the pups’ mother, the DNR’s Sampson said.
“There’s no doubt she’s going to know we’ve been here,” Sampson said. “The question is whether it’s enough to make her move them.”
“Any time you visit the den of an animal, at some level there’s an effect,” Erb said. “Our early experiences combined with results from pup studies in Ontario and Idaho suggest that some will move pups to a new den after a visit.”
But there’s no information yet, he said, that it has any important effect on pup survival, even in studies that have deployed radio-collars on pups or surgically implanted radio-transmitters.
And often, wolves change den sites even without human intrusion, he added.
A wolf pack and its pups typically remain associated with a den site through early to mid-summer, Erb said. Later in summer, the pack often moves to a so-called rendezvous site. The pups are more mobile then, he said, but are not yet hunting with the pack. In fall, when the pups are large enough, the rendezvous site becomes less important, and the young wolves begin traveling more with their parents.
According to the DNR’s research, Minnesota has an estimated 374 wolf packs. The average number of wolves in a pack at mid-winter was 5.1 in 2015, according to the agency. Pack size typically doubles once pups are born in the spring. But not all of them survive through the next year. Along with some mortality among adult wolves, that typically brings wolf numbers back down to near the previous mid-winter’s level, researchers say.