Declining Moose Populations: What Does the Future Hold?

Declining Moose Populations: What Does the Future Hold?

Photos by Susan C. Morse

Nineteenth century author Henry David Thoreau marveled at the huge beast he saw deep in the Maine woods. Hoof to withers, the bull stood nearly seven feet tall – taller than the biggest horse. Today, people are just as awed by their encounters with moose. An estimated 80,000 moose live in the Northeast, which practically guarantees an opportunity to see one. Moose imagery is ingrained in popular culture, from the moose festivals that pop up all around New England to the Rocky Mountain microbrew named Moose Drool. Countless cottage industries profit from moosey novelties like moose drop chocolates (which aren’t real) and moose turd necklaces, earrings, and Christmas ornaments (which are). Perhaps the weirdest moose mania happens at the Talkeetna, Alaska, “Moose Droppings Festival,” where enthusiasts in hot air balloons release thousands of moose pellets (real) upon a cheering crowd.

Both majestic and whimsical, moose do indeed seem larger than life. And yet, after decades of recovery, moose populations have started to decline in some areas of the West, the upper-Midwest and the Northeast. Predators, including wolves, human hunters, cougars, bears, and even coyotes kill moose. Moose even kill each other upon occasion as rut-crazed bulls sometimes gore one another with their antlers. But even when confronted by their greatest enemy, the wolf, predation shouldn’t be enough to send an otherwise healthy moose population into decline. Healthy, prime-aged moose are quite capable of beating back canid attackers; deft kicks with heavy sharp hooves cause pack members to experience fractured skulls and debilitating broken ribs and legs. Renowned researcher Rolf Peterson has witnessed some 200 wolf-moose confrontations during his decades of research on Isle Royale, an island in Lake Superior. Only 10 moose were killed; the rest stood their ground and survived to watch their assailants retreat.

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Counting winter ticks.

So what is causing thousands of moose deaths each year, in places as varied as Utah, Oregon, Wyoming, Colorado, Montana, Minnesota, Maine, New Hampshire, and Vermont? Understandably, the answer is complex: there appears to be not one, but a whole panoply of problems that are combining to stress and kill moose. There are some key commonalities, however. Parasites, disease, and malnutrition appear to be interacting in lethal ways, and warmer temperatures associated with climate change appear to be exacerbating the problem.

Rocky Mountain Lows

For years, I relished the chance to observe and photograph moose in Wyoming’s Teton Mountains and Jackson Hole valley. But by the late 1990s, things had changed. It was subtle at first, but by 2005 I was lucky to find moose, and when I did, they didn’t look well. September bulls should be visibly fat, with newly polished antlers ready for the rut. Handsome cows should look sleek in their shiny new winter coats. Instead, bulls and cows alike appeared listless, thin, and disheveled. Oddly, velvet still clung to the males’ antlers. Biologists were alarmed to discover that herd pregnancy rates were reduced to roughly half of normal. A cow’s ability to ovulate, conceive, and give birth is a vital measure of the herd’s productivity. Biologists suspected that a combination of environmental factors were at play. Extensive fires, coupled with the severe droughts of the 2000s, harmed moose by destroying the forest’s thermal cover and drying up the wetland habitats favored by moose for mineral-rich aquatic plants. In British Columbia, pine beetles have destroyed more than 33 million acres of pines, and scientists suspect that the loss of forest cover has led to an increase in both human and animal predation.

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Carotid artery worm.

Finally, a parasite called carotid artery worm (Elaeophora schneideri) has had an increasing and detrimental effect throughout the West. The nematode is transmitted from mule deer, via horse flies, to moose or elk, where mature adult worms come to occupy the carotid arteries. Blood flow is restricted, causing fatal damage to the optic nerve and brain.

Minnesota Muddle

Minnesota’s disappearing moose have gotten a lot of press. Both of the state’s northern moose populations have precipitously declined, with the northwest population dropping from 4,000 to less than 100 and the northeast population dropping more than 50 percent in less than eight years. A multi-year moose mortality study was launched, and researchers have performed extensive field and laboratory necropsies. Biologists have discovered an impressive list of contributors to deaths, including a whole host of parasites, including meningeal worm, also called brainworm (Parelaphostrogylus tenuis), winter tick (Dermacentor albipictus), and liver flukes (Fascioloides magna). Another parasite – a tapeworm of the echinococcosis type – is also compromising moose respiratory function and stamina, which can cause affected animals to be more susceptible to wolf predation. This tapeworm is, ironically, carried by wolves and causes debilitating hydatid cysts, which clog a moose’s lungs.

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Moose browsing has completely high-lined the balsam fir throughout this area.

Many of the dead moose also show signs of exposure to a variety of disease agents, including West Nile virus, malignant catarrhal fever, Lyme disease, and eastern equine encephalitis. Most victims were malnourished and in poor condition, even during times of the year when food supplies are plentiful. Many of the moose “tip overs” were thin and malnourished, yet they had full stomachs. Dr. Michelle Carstensen, Wildlife Health Program supervisor for the Minnesota Department of Natural Resources, said that while volumes of data have been collected, “There is still no smoking gun at this time; there is not enough data yet to answer with certainty why Minnesota’s moose population has dropped 52 percent since 2010.” Parasites, novel viruses, systemic infections, predation, contaminants, and nutritional deficiencies – or likely some combination of these – may eventually prove to be the answer. In the meantime, Carstensen and her colleagues are invested in researching the possible relationship between global warming’s elevation of ambient temperatures and how heat stress at critical times of the year may compromise nutritional well-being and fitness, predisposing moose to greater risk of death from parasites, disease, or predators.

Moose Declines in the Northeast

Thirty-three parasite species are known to affect moose, but winter ticks are a particularly gruesome killer – a scourge that causes their victims unthinkable suffering. Last April, I participated in a field necropsy of a calf that had died in Maine. She was one of 60 cows and calves that had been radio-collared for a study conducted by moose biologist Lee Kantar and his colleagues at Maine’s Department of Inland Fisheries and Wildlife. Half of the collared moose died this past winter, including 22 calves and 10 cows, in what was the worst winter tick epizootic anyone could remember. The loss prompted the state to reduce hunting permits by nearly 1,000 tags for the fall 2014 season.

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Heavy moose brooming up close.

The calf’s radio telemetry mortality signal led us to her. She lay sprawled under the spruces where she had collapsed. She died mid-stride and never even attempted to lift her muzzle out of the snow, where it was driven when she fell. Amidst a sticky goo of blood, tick feces, and broken hairs, we found an estimated 40,000 ticks. Clusters of engorged female ticks were still attached to her skin, where in recent weeks they had collectively contributed to fatal blood loss. Kantar and his team members recorded a number of problems that contributed to the calf ’s death. She was malnourished, her lungs and body cavity were filled with fluid, her kidneys were infected, and acute anemia triggered her body systems to break down. When the results of that winter’s (2013-2014) study were tallied, Kantar was disturbed by a higher-than-expected mortality of calves, as well as some adult cows. But this past winter, he and his colleagues were encouraged by “continued strong numbers” of moose observed during the first three aerial surveys conducted. “We still have lots of moose out there, and we hope that normal fall and winter weather can help break the pattern of such heavy tick loads in the coming years,” he said. “We continue to be optimistic, but at the same time cautious about what periodic winter tick infestations, coupled with other increased parasite loads (meningeal worm, lungworm, and hydatid cyst tapeworms) mean for moose in Maine. The frequency of these events and associated increased mortality will be a significant driver in population growth or decline.”

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This marrow core indicates that the dead moose calf was extremely malnourished.

Researchers Anthony Musante, Peter Pekins, and David Scarpitti, of the University of New Hampshire’s Department of Natural Resources, have estimated the metabolic effects of winter tick infestations on moose calves. They found that calves are more vulnerable because of their smaller size, proportionately smaller stores of body fat, and greater metabolic demands. Blood loss associated with moderate (30,000) to severe (70,000) tick infestation has a substantial effect on an afflicted calf ’s energy and protein balance. During March and April, female ticks dramatically increase their blood consumption as they prepare to abandon their moose hosts and lay eggs. The researchers estimate that as much as 112 percent of a calf ’s total blood volume may be drained over the eight-week engorgement period. The most critical metabolic impact is the loss of protein that occurs as a result of such blood loss – as much as 50 to 100 percent of a calf’s daily requirements. “There is little or no digestible protein in winter browse that can enable a calf to recover such a loss,” said Pekins. If a calf can’t sustain the energy demands for blood replacement, weight loss, catabolization of muscle tissue, and a host of other physical disorders, acute anemia, and malnutrition will combine to cause death.

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Snails and slugs serve as intermediary hosts for brainworm.

Biologists throughout the Northeast agree that winter ticks are the major contributor to moose declines; however, other stressors affect moose fitness. For example, within industrial forest lands in the northern portions of Vermont, New Hampshire, and especially Maine, clear cuts have contributed to the production of abundant foods favored by moose, which have supported greater densities of moose. But more is not necessarily better. In some places, moose numbers have exceeded the carrying capacity of even the most browse-rich habitats. In northern Maine and the Northeast Kingdom of Vermont, I have been stunned by the totally wrecked “moose pastures” – acres upon acres of disfigured plant growth that will never become a healthy forest.

Cedric Alexander, Vermont’s moose biologist, is happy with his department’s past efforts to lower moose numbers in the Northeast Kingdom. Browse pressure on Vermont’s northern habitats has since been noticeably reduced, and less heavy herbivory has enabled trees and shrubs to recover. Healthy forests get to grow and provide cover and more nutritious foods for moose and other wildlife. Alexander believes that his department’s efforts may have spared them the worst of this past year’s tick epizootic. More moose support more ticks, which in warm fall and spring conditions successfully attach to more moose, feed, breed, and lay more eggs to start the cycle all over again. “We are also encouraged by the results of Vermont’s fall moose tick count. Overall, we had a 41 percent drop in tick numbers. What is best for moose is good old-fashioned winters with frosty autumn weather, a cold spring, and a lingering snowpack.”

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Engorged winter ticks.

Biologist Kristine Rines, of New Hampshire’s Fish and Game Department, has been the state’s moose project leader for 28 years. She says that in New Hampshire the moose herd has declined approximately 40 percent during the past decade. “What we found in the 2001 to 2005 period was that a warmer fall and winter weather pattern was becoming the norm in New Hampshire,” said Rines. “As a result, our moose are carrying heavy tick loads almost every year, resulting in increased mortality and lower body weights with an associated drop in birth rates. To further complicate the picture, in the southern part of the state, where moose densities are low and winter ticks are not as abundant, brainworm is causing high mortality in moose. This parasite is carried by whitetail deer, and the more deer you have, the more brainworm. Meningeal worms cause no harm to deer, but when moose ingest the larvae the parasites migrate to their nervous system with devastating effect.” As temperatures become more moderate, increasing deer numbers could add to moose problems, even in what has been considered to be the best moose habitat in the Northeast.

The connection between a warming climate and cold-adapted species decline goes beyond moose; something I’ve seen firsthand in my travels. Studies show that 34 of the world’s 43 major caribou herds are also in steep decline. Rines is outspoken in making this connection, saying, “We are faced with a changing climate, which in turn is changing the species composition of our wild world. Will we care enough to address the factors that are causing climate change? If we do not, we must be prepared for a New Hampshire with far fewer moose, shrimp, and purple finch, to name a few species that are currently in decline.”

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A healthy, tick-free moose in summer.

Population declines of moose and other cervids is nothing new, but this doesn’t make the current decline less worrisome. The biologists I spoke to expressed optimism in the abundance and diversity of moose research and monitoring efforts that have been launched in recent years. In-depth collaborative research projects are being conducted in Maine, New Hampshire, Massachusetts, and New York’s Adirondack Park region. In addition, wildlife action plans for all northeastern states stress the critical importance of securing healthy and whole habitats for the benefit of wildlife.

Susan C. Morse is founder and program director of Keeping Track in Huntington, Vermont.

 
Discussion
  1. csblackburn → in Laramie, Wyoming
    Oct 19, 2016

    Those winter ticks are nasty. I can’t believe a researcher found 40,000 of them!!

  2. Sue Baker → in Baden
    Sep 10, 2017

    Maybe they should cut down the annual slaughter, and let the poor things regenerate?

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