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Winter ticks are a growing threat to moose calves in Maine

The parasites are linked to a record mortality rate this year in moose calves in remote Somerset and Piscataquis counties.

ROCKWOOD, Maine — This week is Tick Week at NEWS CENTER Maine, where we are bringing you the latest science on vaccines and preventative shots against Lyme disease and how newly discovered bacteria carried by deer ticks is linked to rare neuropsychiatric conditions in children.

Now, we are focusing on winter ticks and their tragic effect on moose calves in northwestern Maine. Unlike deer ticks, winter ticks don't carry diseases, but survive on the blood of animals and are commonly found on moose. 

Last winter, nearly 90 percent of the moose calves tracked by biologists didn't survive their first year, and experts say winter ticks are the reason. 

Winter ticks killed the largest percentage of moose calves this year since the Maine Department of Inland Fisheries and Wildlife started its moose surveys more than eight years ago. 

As our changing climate brings shorter winters in Maine, which is also helping winter ticks thrive, it is also making young moose even more vulnerable.

Moose are the official animal of the pine tree state. At about 70 thousand strong, Maine is the home to the largest population of moose outside of Alaska. The big draw is an abundance of commercial forest land, considered prime moose habitat. 

But there is a new threat to their survival. A tiny parasite that is literally sucking the life out of young calves.

"You see that moose are losing 25 to 30 percent of their body weight, in 12 weeks that's a recipe for death," Maine Moose Biologist Lee Kantar explained.

Kantar says the culprit is winter ticks, also known as moose ticks, which have been pestering moose for more than a century. Since 2014, Kantar has tracked moose populations, including the mortality rate in collared calves.

Each winter, teams in a helicopter capture moose and release them after fitting them with a GPS collar. Biologists track their patterns, including text alerts when an animal has likely died. 

Kantar says it's not unusual to find an adult moose with as many as 90 thousand ticks. Fully engorged, winter ticks resemble large raisins. Each adult female tick is capable of draining a milliliter of blood. Both adults and young calves will often rub themselves bald trying to scrape them off, while others just don't make it.

Griffin Dill is the manager of the University of Maine Cooperative Extension Tick Lab. 

"Winter ticks stay on that one animal, go through an entire life cycle, molt on that animal, and then drop off," Dill explained.

He says unlike deer and dog ticks, winter tick larvae cluster in clumps on vegetation including harvested trees. He says in early fall, winter ticks "hitch a ride" on a passing moose.   

"The moose can pull a chain of anywhere from a few dozen to a few thousand, in one swoop," Dill said. 

But a growing number of calves, even at more than 400 pounds, can't survive the blood loss amid harsh winter conditions. 

"If they only have ten thousand on them, they can make it and survive to their first birthday, but when they have 60 thousand they can't," Kantar said. 

The parasites are taking the biggest toll on young moose in parts of Piscataquis and Somerset counties, including off of a logging road that Kantar showed NEWS CENTER Maine, just west of Rockwood near Moosehead Lake.

86 percent of the collared calves being tracked in these remote areas died by early May less than a year after they were born.

It's the highest death rate since the Maine Department of Inland Fisheries and Wildlife began tracking surveys. Another troubling trend, surviving the loss of gallons of blood from huge tick loads over the winter is also taking a toll on pregnant moose, resulting in a decline in the calving rate. 

Warming temperatures are also allowing winter ticks to quest on moose longer.

"We are getting longer falls, we are not getting that permanent snow that we used to," Alexej Siren, a postdoctoral researcher at the University of Vermont, said. 

Siren works with Kantar and biologists in Vermont and New Hampshire. He says research is underway if managing harvesting on commercial timberland could have an impact.

"[It's] so [the moose] don't use the same areas where the adult female [ticks] are dropping off of them in the spring, and [to] keep [the moose] from going back into those areas in the fall and re-infecting themselves," Siren said.

Maine is allowing hunting in half of a 2,000 square mile wildlife management district, known as Zone 4. It runs from the Canadian border to the boundary of Baxter State Park in an effort to try to lower the tick population.

"The answer is less of those moose to break the cycle so you don't have these calves taking the bulk of it," Kantar added.

For more information on Lyme and tickborne co-infections from the Maine CDC, including real-time data of reported cases, click here. 

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