Peter Pekins can recall the first sign of trouble. It was spring of 2002, and Pekins, a professor of ecology at the University of New Hampshire, was leading a state-sponsored study of the local moose population, which was ailing for no apparent reason.

"I remember sitting down here and getting a call, 'I got another dead calf here,'" he said. The moose population had flourished in the previous decade. Yet all of a sudden, something was wrong. Calves were dying. "We went up and took a look and pulled it out and saw all those ticks in there. And so that was the start of all this."

"All this" has been the halving of the state's moose population, largely due to an insidious parasite called the winter tick. The arachnids have been latching onto moose by the tens of thousands across northern New England, killing calves and leaving adults weakened. While they are native to the region, the ticks have been thriving as climate change has shortened winters.

"Moose numbers will decline because of this. There's absolutely no question about it," said Kristine Rines, the New Hampshire Fish and Game Department's moose biologist. In some northern counties, ticks killed about 75 percent of calves in the winters of 2013-14 through 2015-16, when snows came unusually late. Reproduction rates are down, too.

The moose mortality crisis, however, might contain its own solution. Eventually, so many moose will die that there won't be enough to spread so many ticks. The cycle, in theory, will break. But how long that takes, and whether the moose population will ever be able to recover, is what Rines and her colleagues are grappling with.

"The question then becomes, do you push the population down to certain levels purposely," she said, "or do you just let ticks kill them off, in what amounts to a terrible death?"

In short, should hunters be permitted to speed up the process?

The dilemma points to a question facing wildlife managers and conservationists throughout the world. Global warming is altering climatic conditions faster than many animals and plants can adapt. Scientists and governments are asking when—and how deeply—they should intrude upon nature to try to preserve healthy ecosystems. Researchers in Montana, for example, have begun moving bull trout to lakes at higher elevations where waters are colder. In England, scientists released marbled white butterflies beyond the northern reaches of their natural range.

'Just a Bag of Skin and Bones'

Each fall, winter ticks spend their days climbing up vegetation and "questing"—groping around with their forelegs, looking for a host. If temperatures drop and snow covers the ground before they've succeeded, the ticks perish. The University of New Hampshire's Pekins points to old photos from the state's deer hunt, which comes in mid-November, to show how times have changed. "All those pictures show deer hunting on snow," he said. "But if you ask a hunter today, when was the last year you hunted on snow? They'd say this year [2016-17], and that would be the only year."

With temperatures above freezing and no solid snow cover until December in many years, the tick population has surged. Moose never evolved the grooming behavior of deer, rabbits or other host animals, leaving them defenseless. Pekins' team has found up to 90,000 of the tiny arachnids on a single calf.

"They're having their entire blood volume drained. Think about that," he said.

Most adult moose survive, though the ticks appear to be harming reproductive health. Calves usually aren't so lucky. By the time spring arrives, he said, "they're just a bag of skin and bones is all."

Tick outbreaks used to strike occasionally. Now it's nearly an annual event. "We've had five of these in the last eight years," Pekins said. "That is just absolutely unprecedented."

This winter offered some respite. An unusually dry fall combined with mid-November snows knocked down tick numbers, and only about 30 percent of the calves monitored in northern New Hampshire and 50 percent of those in western Maine have died. While he welcomed the news, Pekins said it doesn't change the overall trend. "I think you have to assume the previous years were more normal," he said, "that winter is going to be shorter."

New Hampshire's moose population has dwindled to about 3,500, from 7,500 in the mid 1990s. The animals are in decline across much of the southern edge of their range, all the way to British Columbia. In Minnesota, the population has been cut in half in a decade. Ontario's has fallen by 20 percent since the early 2000s. Ticks aren't the only culprits. Another parasite, called brainworm, has plagued moose. And the warmer temperatures alone may contribute. In northern New Hampshire and western Maine, however, Pekins and his colleagues say the winter tick is the primary cause of the decline.

The public, appalled by what's happening, has proffered all sorts of solutions, from turning loose tick-devouring guinea fowl to deploying insecticide-spraying robots. Wildlife officials, however, say the only effective solutions would be to reverse global warming or to have fewer moose.

Too Many for Their Own Good?

Alces alces—the scientific name of the moose—nearly disappeared from New England in the 19th century, a result of unregulated hunting and the clearing of forests. By 1950, New Hampshire was home to only about 50 moose. But as farmland turned back to forest and states began regulating hunting, the giant ungulates bounced back. In recent decades, they found ideal habitat among the mechanized logging operations of Maine, said Lee Kantar, the moose biologist with the Maine Department of Inland Fisheries and Wildlife. The timber industry provides a constant supply of new tree growth, the animal's primary food.

Kantar wonders whether the recovery was, in a sense, too successful. "The denser any population of wildlife species is, the more prone they are to have certain parasites," he said. The ticks do not appear to present as much of a problem in southern New Hampshire—though brainworm has been killing moose there—or in Vermont, where populations are thinner. "The question we were left with was, was it too many moose for their own good?"

Kantar plans to propose a trial in a small portion of the state, in which his department would issue more hunting permits than normal to thin the moose population. Once moose numbers reach a certain threshold, scientists hope, there won't be enough to spread the tick efficiently. It's unclear, however, exactly what that threshold is.

Ticks are killing young moose. “They’re having their entire blood volume drained. Think about that,” Pekins said. Credit: Peter Pekins/University of New Hampshire

Last year, one of Pekins' students modeled exactly such a scenario in a master's thesis. Using data from the New Hampshire study and others, the paper indicated that it would take 15 years in one northern portion of the state for nature to thin the herd enough to reduce the tick population. If the state were to issue three to six times more hunting permits—killing between 90 and 190 animals annually in that part of the state, rather than 15 to 50—the population would reach the threshold in just five years, according to the model.

Such a move would turn conventional wildlife management on its head and run contrary to what New Hampshire state officials perceive as a program to save the moose. As the population has plummeted over the past decade, the state has slashed the number of annual hunting permits from a peak of 675 to a proposed 51 for this fall. The current management plan would actually halt hunting if the numbers drop below certain levels. Accelerating the hunt instead would be extremely controversial.

"It's an iconic symbol of the North Country," Pekins said. "The beer companies have moose on their labels. The art galleries have moose. The motels have moose. It represents northern New England. If your clients came up to your motel and they thought they had no chance to see a moose because the state reduced the density in half, who knows how people react to that."

Officials have only just begun to float the idea publicly, but some conservationists and hunters already are opposed.

"We never want to endanger the resource. That's been the hunter's creed for generations, and I've always believed in it," said John Harrigan, a long-time outdoors columnist and hunter who lives in northern New Hampshire. Harrigan is also the co-founder of the New Hampshire Wildlife Coalition, a local advocacy group, and he's argued for ending the moose hunt. "When push comes to shove, we hunters need to back off."

"We don't know what's going on right now with climate change and the ticks," he said. "It's a little bit arrogant to think that our actions on the wildlife scene can really have the kind of effect that we think it will."

Kent Gustafson, wildlife programs supervisor for the New Hampshire Fish and Game Department, said his agency will wait at least until the end of this year to see the results of Pekins' work before deciding to increase the number of permits.

"The simplest thing to do would obviously be to let nature take its course," Gustafson said. "Moose is one of the iconic species in the state, and there are a lot of people who would like to see not only moose to continue to exist here, but also to continue to exist here in a healthy state. And that may require doing some things that are counterintuitive."

Even if the state does expand the hunt, Gustafson said, it may be only a patch on a larger wound. "Long term, who knows," he said. "We're talking about a species that is existing on the southern end of its range in North America. If in 150 years from now, New Hampshire has the climate of Virginia, things aren't going to be looking very good regardless of what people try to do."