Winter ticks plague Vermont’s moose herd

VERMONT — Archers will head into the woods on Saturday for the start of moose season and hunters with guns will get to take their shots beginning Oct. 15. But fewer hunters will be roaming Vermont’s forest this fall on the lookout for one of the state’s most iconic animals.
This year the Department of Fish and Wildlife issued 40 percent fewer moose permits (160 in total) and again restricted hunting in all but two management areas to adult males, in an effort to bolster a herd hit hard by a pesky arachnid that is also a growing nuisance to humans — ticks.
Moose, it turns out, are not good groomers. And that evolutionary detail, hitched to three-and-a-half centuries of landscape-altering European intervention, are behind the current challenges besetting the state’s moose herd, according to biologist Cedric Alexander, Fish and Wildlife’s Moose Project Leader.
After decades of record numbers and thriving populations as moose reclaimed their ancestral turf, for the past half-dozen years a “winter tick epizootic” (think “epidemic,” but for animals) has put the herd in decline.
The damaging explosion of this parasite goes back hundreds of years to when Vermont’s virgin forests were cleared for settlement. Two-hundred-fifty years ago the Green Mountain State was 95 percent forested.
“We changed all that,” said Alexander. “We made this state into an agricultural landscape. We cleared 70 percent of it. The moose were driven off.”
By the end of the 19th century, habitat loss and overhunting had largely wiped both moose and deer both off the Vermont landscape.
But human patterns again changed, as Vermonters fled the stony fields and hill farms of the Green Mountains for greener pastures out West.
“Especially when the hill farms were given up due to the West being opened up, and people dying in the Civil War, and markets changing for sheep and so on and so forth the land reverted back to brush lands,” Alexander explained. “And the combination of the agricultural lands that hung on and the brushlands was all ideal for deer.”
As Vermont’s forests regenerated, the moose returned. By around 1980, the state was once again 80 percent forested and by 1993 there were enough moose that the state instituted a managed hunt, to keep the herd in balance in the absence of their former predators, wolves and panthers.
But the ecological balance of this reclaimed landscape was now altered. The intricate, delicately interlocking web of life developed over eons was stitched back together in ways that didn’t quite fit right — not for moose.
In this newly reforested Vermont, moose and deer (both members of the cervid family) now overlapped their ranges, in ways that hadn’t happened before European settlement — in ways, it turns out, that are bad news for moose.
“Moose didn’t really evolve through the eons on the same latitudes with deer. Deer only started intermixing to a greater level after we changed the habitat,” said Alexander.
“So for the first time we have relatively dense deer numbers in northern Vermont, whereas when the Abenaki were existing up here anything north of Route 2 especially and probably north of Route 4 was mainly moose. And that’s what they survived on.”
Deer brought with them their parasites — winter ticks and brainworm — but these were parasites that deer had evolved with and had good defenses against.
Not so the moose, for whom these newly introduced parasites — new in evolutionary terms — can be devastating.
“So now you have this other species of cervid that’s present on the landscape when moose are expanding back in through Vermont and Maine and northern New Hampshire. And now moose are encountering winter ticks because these ticks live on deer,” said Alexander.
Deer can handle these ticks, in part, because they are “programmed groomers,” Alexander said.
“They will groom themselves every day just out of habit,” he continued. “And they’re also more agile and adept at reaching areas with their tongue. So only a few ticks survive on deer, and it’s not in any way debilitating to them.”
This “programmed grooming” gives deer an advantage in what scientist Bill Samuel calls the “evolutionary arms race between ticks and hosts.” Deer groom before the tick can latch on. Not so moose.
Alexander estimates that by April, towards winter’s end, a typical Vermont moose can be carrying up to 70,000 ticks. That’s more than enough bloodsuckers to be debilitating, especially when you consider that they can grow to the size of your little finger.
“Moose … don’t seem to even feel the larvae and the nymphs feeding on them,” he said. “It’s only when the ticks molt into adults in late February or March that the moose start grooming but by that time — because they’ve got 30,000 to 70,000 ticks on them — they end up actually causing anemia because of all the blood lost at a time of year when the moose is already on a nutritionally deficient diet.”
The greatest mortality is among calves.
“Ticks are a huge problems for the calves because when they brush against these we call them ‘tick bombs’ (ticks cluster in the fall in huge clumps of hundreds or thousands) it doesn’t matter if you’re a big bull that weighs 1,400 pounds live weight or a calf that weighs 300 pounds you get the same shot of ticks.
“Proportionately it’s five times worse,” for a calf, Alexander said.
“The calves, especially, which go into the winter without much fat reserves to begin with, are susceptible to dying. Of course, they’ve rubbed off and broken off a lot of hair. So they’re susceptible to exposure if there’s a freezing rain and then they have no way to stay dry or stay warm when it drops down cold and freezes up again and they’ve lost all this energy.”
Global warming is also contributing to the moose herd’s tick problems.
A couple decades ago, said Alexander, winter ticks might fall off a deer in April and hit snow and get eaten by birds or just die. Now in a warmer, snowless April, they hit bare ground, crawl into the underbrush and live. Whereas before, snow might come in October and November and again, help wipe out that year’s batch of ticks, we’re now seeing Decembers with hardly any snow at all.
These trends make conditions better and better for ticks to survive and breed and keep sucking the life out of moose for longer periods.
A secondary concern, said Alexander, is that moose don’t like it hot. True northern animals, they prefer the cool. But as summers get incrementally hotter, the moose spend more time trying to cool off and less time eating. The heat makes them less energetic and more lethargic.
Still, it’s the ticks that are wildlife officials’ main concern.
Nevertheless, state wildlife officials are hoping to see better calf numbers this year, given that last year’s hunt put female moose for the most part off limits.
“May and June is when the calves are born, (and) this is the first year we’ve had cows giving birth that might have otherwise been taken by a hunter last fall,” Alexander said. “So they’re out there producing calves, and we should see an increase in sightings this fall. If we don’t then we’ll have to look at all the data.”
One aspect of Fish and Wildlife’s strategy to address the winter tick infestation is to find a healthy balance of moose on the land. This year’s reduction in hunting permits and limits to bulls addresses the herd’s current decline. But a decade or so ago, the concern was a spike in numbers, especially in the Northeast Kingdom. The department is working to establish a long-term moose density — geared to different habitat areas around the state — that maintains a healthy herd and a healthy landscape.
“Our current 10-year moose management plan (2010-2020) should continue to help address the tick issue by maintaining lower moose densities (no higher than 1.75 moose per square mile) in the Northeast Kingdom and even lower densities throughout the rest of the state,” said Alexander.
This winter, the department will conduct its first collared moose study. It will investigate rates and causes of mortality, including deaths caused by ticks.
“Hopefully we’ll have a bunch of GPS collars on cows and calves by the end of January and we’ll get some good data from that,” Alexander said.
Reporter Gaen Murphree is reached at [email protected].

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