Winter ticks are increasing in the warming climate, and they're killing moose calves

SCOTT SIMON, HOST:

Maine is home to more moose than every state except Alaska. But in one of the moosiest (ph) parts of Maine, nearly 90% of moose calves tracked by biologists last winter didn't survive their first year. Maine Public Radio's Kevin Miller joined a biologist studying the connection between ticks, climate change and this icon of the North Woods.

KEVIN MILLER, BYLINE: In the winter of 2014, Maine biologists captured a young moose, fitted her with a radio collar, and released her back into the wild. Moose No. 59 roamed the aptly named Moosehead Lake region for eight years until a man stumbled upon her fresh carcass this spring and dialed the phone number on her ear tag.

(SOUNDBITE OF FOOTSTEPS IN GRASS AND LEAVES)

LEE KANTAR: She's a little stinky, but...

MILLER: This is her?

KANTAR: Yep.

MILLER: Moments after bushwhacking to her final resting place, state biologist Lee Kantar starts reconstructing Moose 59's final chapter. He points to her bony hips, patches of missing hair and a prime suspect in her death.

KANTAR: There's winter ticks all over her. So you can see how big they are.

MILLER: The moose has been dead about four days, yet the carcass is literally crawling with big, brown ticks, while countless more are still attached and fully engorged. Before collapsing, Moose 59 might have been covered with 50,000 to 90,000 of the parasites. Winter ticks are not a new pest for moose, but their numbers have exploded in parts of Maine, New Hampshire, Minnesota and southern Canada as the climate warms. The results can be deadly - in this case, doubly so, as Kantar explains.

KANTAR: I have a calf here, just so you know. It's not my favorite thing.

MILLER: Oh.

He gently removes an unborn calf from the cow's carcass. It's tiny - just 12 pounds and about two feet long. Kantar explains that mom was probably 2 to 3 weeks from birthing. So even if she had survived, the severely malnourished calf wouldn't have.

KANTAR: So I don't like to see this. I'll tell you that much, but...

MILLER: Kantar has seen more dead moose calves than ever this spring. Sixty of the 70 calves that the Maine Department of Inland Fisheries and Wildlife began tracking last winter had died as of early May. That's 86% mortality. As many as 75,000 moose roamed Maine's forests a decade ago, thanks to prime habitat created by timber harvesting. But their numbers are falling here and in neighboring New Hampshire, where state biologist Henry Jones says ticks are the biggest factor in the White Mountains and areas north.

HENRY JONES: So essentially, you had this species - moose - that came in and found all this food, no predator. Their population exploded. Now, it is coming back down. Winter ticks are acting as a predator in the system, and they are enhanced by the shifting climate.

MILLER: Unlike deer and dog ticks, winter ticks hunt in packs. Larvae gather in interlocking clumps on vegetation. And when one ticks snags a passing victim, hundreds or thousands more come along for the ride. A solid coating of snow or a sustained cold snap will kill the larvae. But snow has been arriving here later in the fall, and that subtle climate shift means ticks have more time to find a warm host. Kantar and his team spend months tracking down animals that didn't make it, like Moose 59.

KANTAR: So when I do these, you know, we take a look at her extremities, her external features. It's basically "CSI."

MILLER: Field necropsies are laborious and messy on animals that can stand more than seven feet and weigh half a ton, so Kantar comes armed with garden loppers, a hatchet and sharp knives. We'll spare you the sound effects, but inside this pregnant cow, he finds bone marrow almost devoid of fat and internal organs that are a sickly white.

KANTAR: She's completely pale. You know, this is - to me, when her organs are this coloration, that's a sign of anemia, meaning she was being fed on by ticks, and she's got so much blood loss that she's - you know, it's showing up everywhere.

MILLER: It can be impossible for some adult moose to replace the literally gallons of blood lost to tens of thousands of ticks, and Kantar says that drain is even more detrimental for calves headed into their first brutal winter.

(SOUNDBITE OF TOOLS DROPPING AND CLANKING TOGETHER)

MILLER: His work complete, Kantar packs up his gear and leaves the moose - now collar free and numberless for the first time in eight years - to rest in the woods she once roamed. For NPR News, I'm Kevin Miller.

(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.