Winter ticks killed a greater percentage of moose calves in northwestern Maine this winter than at any time since state biologists started conducting radio-collar moose studies in 2014.

The results of this winter’s study are concerning to wildlife officials across northern New England, but Maine biologists are hopeful that measures to decrease moose density in the study area could result in a healthier herd.

Sixty of 70 radio-collared calves – or 86 percent – in Wildlife Management District 4 died as a result of winter ticks, said Maine Wildlife Division Director Nate Webb. The study is now in its third year in northwestern Maine. Previously, the moose-collar study was conducted around Moosehead Lake and far northern Maine.

“We’ve had other years when calf mortality was in the 70-percent range,” Webb said. “And calf mortality naturally fluctuates from year to year. We don’t feel this one high year is necessarily an indication that the rate we did observe will continue into the future. Our hope is that this year is an anomaly, and we do believe it is.

“It is a concern. But it points to the important work being done in WMD 4 in the adaptive hunt to try to determine if we can reduce the impact of winter tick on moose.”

Last year, the state gave out an additional 550 cow moose permits in a section of the hunting district, now called WMD 4A, which is north of Moosehead Lake and west of Baxter State Park along the Canadian border. Wildlife officials wanted to test the theory that an increased harvest in an isolated area over five years will help to decrease the winter tick parasite. Those extra permits will be allotted again this year in what officials call an adaptive hunt.


In March, state moose biologist Lee Kantar said his overall impression of the adaptive hunt’s first year was positive, though it would take five years to test the theory.

Winter tick infestation is exacerbated by a warming climate, according to the Maine Department of Inland Fisheries and Wildlife. The parasite now survives in greater numbers in Maine’s core moose range than ever before, IFW reported. In addition, a University of Maine study showed that winters are two weeks shorter on average than 30 years ago.

In 2012, IFW reported that Maine’s moose population was about 76,000. The herd is now estimated at 60,000 to 70,000, Webb said, adding that in some parts of the state moose densities are as high as five to eight per square mile.

“That’s far higher than you typically find across moose range across the continent,” Webb said. “Typically moose are somewhere around one moose per square mile in Alaska and Canada. The density in Maine is quite high.

“Basically what we’re hoping is to incrementally bring the moose density down to see if there is a corresponding response in the population with calf survival. I don’t think in all likelihood we’ll bring the density to one moose per square mile. But we hope to bring it down quite a bit.”

Webb pointed to New York as an example, where there are low moose densities in the Adirondack Mountains and very minimal impact of winter tick.


Results of this winter’s radio-collar survey in northwestern Maine were first reported by Maine Public Radio.


In New Hampshire, biologists are concerned with the high calf mortality in Maine – particularly because a radio-collar study conducted there from 2014-19 found a mortality rate higher than 60 percent for five of the six years, said Dan Bergeron, New Hampshire Fish and Game’s wildlife division director.

“We’ve had a number of years when we’ve noticed a high mortality in our calves. We’ve documented mortality as high as 80 percent,” Bergeron said. “Moose calf mortality normally is around 20 to 30 percent.”

The moose population in New Hampshire is estimated at 3,000 to 3,500 moose, though the highest densities of moose are only 1.6 per square mile, Bergeron said.

“By and large we still see a decline in moose, but it’s slowed,” Bergeron said.


The high calf mortality in northeastern Maine also concerns biologists in Vermont, where a radio-collar study was conducted from 2017 to 2019. Nick Fortin, Vermont’s deer and moose study leader, believes the decline in moose numbers there has stopped.

“It’s concerning because we know the tick numbers and impact ebbs and flows similarly across the whole region. So a bad year in Maine is a bad year here in Vermont. That said, we have no evidence that it was a bad year in Vermont. We feel our moose herd has kind of stabilized,” Fortin said. 

Ten years ago the Vermont Fish and Wildlife Department intentionally decreased the moose herd – but not because of winter tick. Moose were over-browsing and destroying the habitat, Fortin said, so the state made a concerted effort to thin the herd. The result: In the northeastern corner of Vermont, where there are the highest densities of moose, the population is stable, he said.

“It’s important to note,” Fortin said, “that our area of highest moose density is still considerably lower than the density of moose in northern and western Maine. So there are some different dynamics at play. The lower density moose might help keep the number of ticks down.”

“Moose are definitely impacted by winter ticks (here). But our current understanding, like all moose managers in the Northeast, is that if you reduce the number of moose, you reduce the number of ticks.”

On Wednesday, the number of proposed moose permits for Maine’s fall hunt – 4,080 – was approved by the IFW Advisory Council. The total permits will increase slightly from last year, with 50 more going to a hunting district around Moosehead Lake.

Maine biologists also proposed 96,340 antlerless deer permits for the fall hunt in the new deer-permit format that was signed into law this spring. The majority of those permits allocated in the annual lottery are in southern and central Maine and the Midcoast region.

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