Minnesota’s wolf population jumped 25 percent in the past year, the Minnesota Department of Natural Resources said Monday, in large part to an increasing northern deer herd.

The DNR said its annual survey showed an estimated 2,856 wolves spread among 500 packs, up from 2,278 wolves in 438 packs in the 2015-2016 survey.

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Wolf numbers had remained flat or declined some for several years before this year’s jump.

DNR officials said the wolf numbers are up because there are more deer in northern Minnesota for them to eat. Higher deer densities after three mild winters allow for more wolves, biologists said. Deer numbers in the wolf range are up about 22 percent over last year.

“Deer are the big drivers of the wolf population, regardless of hunting and trapping seasons, unless you are being really extreme in the harvest,” said John Erb, DNR wolf research scientist, told the News Tribune. “When deer numbers go up, wolf numbers go up.”

But wolf numbers also have recovered after two years of not being hunted or trapped. Minnesota held fall hunting and trapping seasons in 2012, 2013 and 2014 before a federal judge in December 2014 ended state wolf management and declared the animals again protected.

That decision was upheld by a federal appeals court and remains in effect, although Congress has threatened to pass legislation to declare the wolves recovered, ending federal protections.

The DNR survey found slightly more wolves per pack - an average of 4.8 compared to 4.4 and that they didn’t need to roam as far to find food. The average pack home territory was down to 54 square miles compared to 62 square miles last year.

Wolves were hunted, trapped and poisoned to near extinction across the continental U.S. until they were given federal Endangered Species Act protections in 1977. A remnant population of a few hundred wolves survived mostly in the Superior National Forest in Northeastern Minnesota.

Under its protected status, Minnesota’s wolf population grew steadily, peaking at just over 3,000 from about 2004 to 2007, and wolves expanded into Wisconsin and Michigan’s Upper Peninsula.

But then northern Minnesota deer numbers began to decline thanks to liberal hunting seasons that allowed hunters to take more deer. Those banner deer hunting seasons were followed by a couple of tough winters in 2013 and 2014.

By the winter of 2012-2013, wolf numbers had fallen back to about 2,200, Erb said. That decline in wolves was in part already happening due to fewer deer, he said, but also because of the state’s first wolf hunting and trapping season that occurred, which took more than 400 wolves.

“That first year we had a season, not only did we take more than 400 wolves through the public season, but there was also another 300 wolves taken (by federal trappers) for depredation control” at farms, Erb said. “Those two combined clearly did impact the population at that point. But all it really did was drive the (wolf) population down to what the deer-carrying capacity was at.”

Although other factors such as competition between packs, disease and run-ins with cars and people all impact wolf numbers, the number of prey typically determines the carrying capacity for wolves, Erb said.

Collette Adkins, senior attorney for the Center for Biological Diversity, said the population jump is good news. She said the unusually large single-year increase shows the impact three hunting and trapping seasons had on wolves. She also noted that the population still hasn’t returned to levels before the state hunting and trapping seasons were held.

“Once again protected under the federal Endangered Species Act, Minnesota’s wolves are rebounding from state-sanctioned hunting seasons,” Adkins said. “To allow further recovery, now we need to defeat Congressional efforts that would strip our state's wolves of the very safeguards that allowed them to bounce back.”

The DNR, hunting and farmer groups disagree, saying wolves have fully recovered from the brink of extinction and can be culled in limited hunting and trapping seasons each year.

It’s not yet clear if wolves have expanded their range south and west in Minnesota beyond what the DNR found in 2013. The next range survey will be in 2018, Erb said.

“My guess, based on sightings and (livestock) complaints, is that the range is still pretty close,” to what it was in 2013, Erb said.

The annual wolf population survey is conducted in mid-winter near the low point of the annual population cycle. A winter survey, often following radio-collared wolf packs, makes counting pack size from a plane more accurate because leafless trees and snow make it easier to spot darker shapes on the ground.

The DNR’s goal for wolf management, as outlined in the state’s wolf management plan, is to ensure the long-term survival of wolves in Minnesota while addressing wolf-human conflicts, especially wolves attacking livestock and pets.

Wisconsin this year estimated about 925 wolves, up 6 percent from last year and 24 percent from 2014-2015. Michigan’s Upper Peninsula has more than 600 wolves.