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Thursday, May 23, 2024

New England’s Moose Are Losing the Fight Against Winter Ticks

On an October morning around sunrise, Josh Blouin was standing outside of an old general store in Island Pond, Vermont, 16 miles south of the Canadian border, getting ready to—hopefully—see a moose. Wearing neoprene boots and a buffalo plaid shirt, Blouin, a wildlife biologist with the Vermont Fish and Wildlife Department, sipped his coffee and explained that he would use telemetry to track one of the massive ungulates, but actually laying eyes on it would require creeping slowly and silently through the woods (which were, inconveniently, covered in crispy fallen leaves). 

For Blouin, it’s a routine. On most days since 2017, he has strapped on hiking boots, rain boots, or snowshoes and trekked into the hardwood forests of Vermont to observe members of the department’s radio-collared moose herd to figure out why the population there has declined by 45 percent in less than a decade. Blouin’s fieldwork has revealed some disheartening numbers, which he and his colleagues published in a paper this summer. On average, from 2017 to 2019, only 66 percent of moose calves survived their first 60 days. Only 49 percent survived their first winter. Birth rates were down by half.

What’s killing these gigantic animals? Teeny, tiny ticks.

It turns out Blouin wasn’t the only one looking for moose that day. Starting in October, winter ticks are “questing”—searching for a host organism—in teams of a thousand or more, interlocking their limbs so that when one tick grabs onto a passerby, they all climb aboard. These ticks like any warm-blooded host, but moose make particularly ideal ones. Not only do moose lack a grooming instinct, but they also offer a thick, eight-inch coat, keeping ticks “nice and warm,” Blouin says. “They’re living in a good life.”

Unlike other ticks, which may spend a few days on a host, transmitting disease in the process, winter ticks hunker down for the season, molting from larvae to nymph to adult over the course of five months, not spreading disease but consuming large quantities of blood. Moose calves, which are about six months old at the onset of winter, and pregnant cows are unable to make enough blood to replenish their systems. By spring they are anemic, malnourished, and disoriented. “They suffer horrible, slow deaths,” Blouin says.

He calls April “mortality month.” That's when radio collars send messages to his cell phone—as many as three a day—that an individual moose has stopped moving. The carcasses Blouin retrieves for necropsy are emaciated, nearly bald, and covered in as many as 70,000 ticks. “These majestic animals are curled up, skin and bones. It’s a sad sight,” he says. Even moose that manage to survive the winter emerge physically depleted and less fertile.

Winter ticks are not new to the landscape, but mild weather brought on by climate change is. Long autumns and late snow give the ticks more time to find a host. Earlier springs are also advantageous to the parasites, which finally drop off the moose in April. If female ticks fall onto snow, they die; if they fall onto leaf litter, they will lay up to 4,000 eggs. In New England, this kind of weather used to be an anomaly. Now it’s the norm.

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“Winter in Maine has been shortened by about two weeks,” notes biologist Lee Kantar, who has spent the last 15 years studying moose for the Maine Department of Inland Fisheries and Wildlife. “That’s a dramatic change in climate.”

In fact, the Northeast is warming faster than any other region in the Continental US. According to the National Oceanic and Atmospheric Administration, the temperature of winter months in New England has risen by 3.6 degrees since the late 1800s. Ice in the region’s lakes now breaks up as many as 16 days earlier as it did back then.

An estimated 75,000 moose live in Maine—the state flag features one reclining beneath a pine tree—and officials like Kantar are concerned that winter tick infestations could soon destabilize the population. For example, a particularly cold year that kills off the ticks could boost the moose population; a warm winter with more parasites could cause a moose die-off. “The change over time is erratic,” Kantar says, and that makes it hard for wildlife managers to ensure the health of the herd and prevent grisly mortality events.

Moose populations have been anything but stable during the last two centuries. Extirpated from New England in the 19th century, thanks to deforestation and unregulated hunting, moose made a comeback in the latter half of the last century. Enticed by the young forests created by commercial logging, they poured into Maine, Vermont, and New Hampshire in the 1970s and 1980s. “It was an amazing recovery,” says Peter Pekins, a retired moose biologist at the University of New Hampshire. “There was a moose behind every tree.”

With plenty to eat and zero predators left, moose populations soared, in some places exceeding their biological carrying capacity. Moose were eating more than their fair share of the woods; collisions with vehicles became commonplace. By the early 2000s, in an attempt to restore an ecological balance, all three states had opened a moose hunt for the first time in more than 100 years.

That’s when, according to Pekins, regional wildlife officials began to see signs that moose populations were declining in ways unrelated to the new hunts. Snowmobilers and shed-hunters reported finding scrawny dead calves out in the woods. In 2002, Pekins led a three-year study of 94 collared moose. The resulting paper was the first to record a calf mortality rate of 50 percent and recognize winter ticks as a serious threat to New England’s moose. Soon, all three states were conducting their own studies and coming up with the same results, Blouin’s included.

Not only were winter ticks thriving in milder weather, these studies found, but also in places where moose densities had skyrocketed. “Covid is a great way to explain the density issue with ticks,” says Blouin. “With Covid, where there is high density of humans, transmission is quite high. Where there are concentrated moose, there are going to be more ticks on the landscape.” In other words, the more ticks that hatch in a given area in April, the more ticks that will be questing there come October.

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Since wildlife agencies can’t restore the lost weeks of winter, all they can do is reduce the density of moose. That means issuing more hunting permits—55 percent more in Vermont and 11 percent more in Maine this year alone. (Officials in New Hampshire have yet to increase permits, despite saying it would result in healthier moose populations.)

It might seem strange at first—killing members of an already declining species. But according to Pekin, density reduction will happen whether it's the hunters who draw blood or tens of thousands of ticks. “There are two choices,” he says. “We can let the thing play out. The density will drop naturally, and the parasite will become less common. Or we can get to that point sooner.”

Not everyone is on board. Blouin says his agency has received “big-time pushback” from anti-hunting groups, which have suggested alternatives like antiparasitic medications, tick collars, prescribed burns to destroy the underbrush where the ticks live, or dousing the woods with insecticides, options that run the gamut from prohibitively expensive to downright impossible. Landscape spraying, in particular, would no doubt have unintended consequences on beneficial insects, as well as the water supply. “It can be difficult to explain to the general public because it’s a super complicated ecosystem-level problem,” Blouin says. “We’re doing the best we can to try to get a grasp on the issue. We want healthy moose.”

During the couple of hours Blouin spent sidling beneath yellow birch and red maples, he found plenty of evidence of moose—big hoofprints and falafel-sized scat. For one heart-pounding second, he came close enough to a cow to hear her snort disapprovingly. But he left the woods without glimpsing a moose. It wasn’t a wholly unsatisfying outcome. But in a world remade by climate change, a hard-to-find moose will be the one that survives. 


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