By Gustave Axelson
Dave Ingebrigtsen keeps hearing the same thing over and over from local folks. "They tell me, 'Dave, I don't see as many moose as I used to,'" says Ingebrigtsen, Department of Natural Resources area wildlife manager in Grand Marais for the past 17 years. "I'm not hearing from anybody who says they're seeing more moose, that's for sure."
Photo Gallery Gunflint Trail Moose
He was skeptical at first, but then he too noticed fewer moose. And he started getting more phone calls about dead moose, including some that appeared to be malnourished despite abundant browse.
"One [moose] stumbled into the road just north of Hovland and dropped for no apparent reason," Ingebrigtsen says." Somebody actually saw it take its last gasp.
"It's obvious the moose haven't disappeared from here, though," he says as he walks through one of his so-called moose pastures in the Pat Bayle State Forest, just off the Gunflint Trail. I tag along, wading through brush and stepping over the 21st pile of moose droppings I've counted in the past half-hour.
What Ingebrigtsen calls a moose pasture is actually a 10-acre forest opening of hazel, dogwood, aspen, birch, and willow saplings. He has used some of his wildlife management budget to shear this shrubby browsing area, strategically located near a shady stand of balsam firs beside a meandering, marshy stream.
"Moose are big and dark, you know. They need places to cool off near where they eat," he says. I nod in agreement, myself a sweltering 220-pound man in a black fleece sweater on this 65-degree spring day.
Ingebrigtsen manages a dozen moose pastures, and he is trying to put more conifer trees on the landscape around Grand Marais -- by planting conifer stands and by encouraging local foresters to do the same. But he acknowledges his habitat management efforts affect just a small portion of the millions of acres of moose range in northeastern Minnesota.
A six-year research study of radio-collared moose has confirmed fears of a declining herd in this range. And while the immediate causes of moose deaths are varied and debatable, the ultimate suspect is climate change -- and habitat that provides thermal cover may be the key to making a warmer Minnesota more hospitable to moose.
After leaving Ingebrigtsen's moose pasture, I drove up the Gunflint Trail to canvass some locals about moose sightings. There are no "Moose Crossing" signs along the 60-mile wilderness road from Grand Marais to Lake Saganaga, because the signs are stolen as soon as they're posted. Legal moose souvenirs can be purchased from the gift store at Voyageur Canoe Outfitters at the end of the trail. Owners Mike and Sue Prom say anything Alces alces is a sure bestseller.
"We've tried selling T-shirts with bears or loons, but the moose items always sell out," says Mike Prom.
The Proms, as well as many of their neighbors, say they see several white-tailed deer but only one or two moose in their travels along the trail, whereas a few years ago they could see as many as 20 moose -- and maybe only a whitetail or two -- on a trip to Grand Marais.
"Since we've lived here, I've never gone a week without seeing a moose," says Sue Prom. "It'll be a sad day if I can't see one."
Stepping into the lobby of the Gunflint Pines Resort and Campground to visit with owner Bob Baker, I have to watch my step so as not to topple a pile of moose shed antlers. Moose sheds lay in stacks on the floor and hang on every wall.
This past winter Baker found 18 moose racks, but the locally renowned shed hunter says he must hunt longer to find moose sheds these days. And he's also finding dead moose during his searches.
"I've found some dead and frozen, with all their hair and completely intact. It's like they were bedded down and sleeping and just died that way," he says. "It's strange. I've never seen that before."
In 2002 DNR wildlife researcher Mark Lenarz launched the study of radio-collared moose in the Isabella area in partnership with the 1854 Treaty Authority (a tribal natural resource agency of the Grand Portage and Bois Forte bands of Chippewa), the Fond du Lac Band of Lake Superior Chippewa, and the U.S. Geological Survey. In the first year of the study, eight moose died -- including four that died bedded down, like the moose Baker found.
"I had anticipated that wolves or car accidents would be the primary causes of mortality," says Lenarz. "It was clear to me then that something was going on."
Over the past seven winters, the project team has followed 116 radio-collared moose. During this time, 85 have died -- including one from bacterial meningitis, six from auto accidents, two from train collisions, five confirmed from wolves, 15 from state and tribal licensed hunters, and two from poachers. Five moose died within two weeks of being collared, possibly from the stress of the capture. The other 49 deaths were due to unknown causes.
While the average nonhunting mortality rate for North American moose is 8 to 12 percent annually, the nonhunting mortality rate of the monitored northeastern Minnesota moose has averaged 21 percent. That's identical to the 21 percent nonhunting mortality rate among moose in northwestern Minnesota, where the herd has plummeted from 4,000 moose to fewer than 100 during the past two decades.
While the DNR's annual moose count from its aerial survey has fluctuated, the northeastern moose population estimate hasn't changed much from around 8,000 since 2005. For a better analysis of moose population dynamics, Lenarz dug deeper into the study data being generated by radio-collared moose. There he found a pregnancy rate that averaged 84 percent, about the same as the North American average of 88 percent and much better than the northwestern herd's 55 percent pregnancy rate.
Then Lenarz and the research team compared the number of radio-collared cows with calves in late April with the cow:calf count from the preceding June. They calculated a calf survival rate of 38 percent. The North American average for calf survival is 40 percent.
Plugging all these numbers -- average annual mortality, pregnancy rate, and calf survival rate -- into a population model, Lenarz calculated a 7 percent average annual decline in the northeastern moose population since 2002. That's a rate small enough to be subtle over a few years, but decimating if it continues during the next decade.
Minnesota's declining moose herd is the exception, not the rule, along the southern boundary of the moose's circumboreal range.
So why would warmer global temperatures affect moose in this region but not elsewhere? "That's a question that's bugged me since we first identified the connection between warmer temperatures and moose survival," says Mark Lenarz, DNR wildlife researcher.
One possible variable, at least in summer, could be humidity. "There has been an upward trend in atmospheric water vapor for some time in our region," says Mark Seeley, a climatologist at the University of Minnesota. "This is reflected in higher dew points, and it is probably not the case in the Northeast." In his book Minnesota Weather Almanac, Seeley points out that since 1995 the number of days with dew points above 75 F -- a humidity level common in tropical rainforests -- has doubled in Minnesota, to more than five days per year.
Drier air in the West and cool ocean air currents in the Northeast and in Scandinavia may help mitigate the effects of warmer temperatures on moose. But Minnesota's increased humidity creates saunalike summer heat-stress days that might weaken the immune systems of our moose.
Michigan: Growing slowly on Upper Peninsula, with pregnancy rate about 70 percent (below North American average of 88 percent). Near 50-year low on Isle Royale.
Ontario: 110,000 and stable for several years province-wide. Local population near Thunder Bay appears to be stressed, with declining numbers and fewer calves counted in 2008 winter aerial survey.
North Dakota: All-time low in northeast corner; stable in central Turtle Mountains; growing in southern and western prairie areas, where farmers complain of crop depredation.
American West: Colorado reintroduced in 1978, increasing in the north but struggling in southern mountains. Recently translocated to Grand Mesa, Colo., and doing well. Growing in northern Utah.
New England: Strong in Northeast, particularly Vermont (three moose per square mile in places). Recently expanded southward into Massachusetts and Connecticut.
Scandinavia: Norwegian herd stable and sustaining annual hunting harvest of 35,000 to 39,000 for past 15 years. Sweden supports annual harvest of around 100,000. In Finland, where annual harvest is 62,500, wildlife managers used hunting to reduce herd to prevent traffic accidents and forest overbrowsing.
The 49 radio-collared moose mortalities in the unknown category have been mysteries, with no identified cause of death. But Lenarz says that doesn't mean there's a single key to solving the mystery.
"The term tipover disease, which has been used because the dead moose seem to have simply tipped over, is misleading because it implies that there is a single cause of these deaths," Lenarz says. "I think it's not one magic disease, but a variety of causes, such as brainworm, winter ticks, other parasites, and diseases that maybe we aren't identifying."
Furthermore, a single moose may be dying from multiple causes.
"If a healthy moose is exposed to low levels of brainworm, the moose can sometimes fight it off," says Fond du Lac Band wildlife biologist Mike Schrage. "But if that same moose is also afflicted with winter ticks or some other health problem, then the combination could be lethal."
Lenarz and his study co-leader Schrage agree that brainworm, winter ticks, and other diseases are proximate causes of moose deaths; and they both suspect the ultimate cause is likely climate change. A pattern, both biologists say, can be seen in declining moose survival rates following hot summers and warm winters.
Moose evolved with bodies built for snowy winters with temperatures consistently below 23 F. They have long legs for stepping through deep snow. A bulbous nose with an elongated nasal passage lined with blood vessels warms freezing air before it reaches the lungs. And a thick winter coat, with an insulating layer of hair beneath a layer of hollow hairs, blocks out the cold.
At temperatures above 23 degrees in winter, moose experience heat stress because their metabolic rate increases as they expend energy to stay cool. Warm winter days have become more frequent in northern Minnesota over the last decade, according to weather records. When three or more of these heat-stress days for moose occurred in January, the study found spring survival rates of radio-collared moose dropped from above 98 percent to the low 90s. The winter of 2006 had 12 heat-stress days, and the spring survival rate among radio-collared moose dropped to 87 percent.
Summer heat-stress days, when temperatures climb above 67 F, also elevate the metabolic rates of moose. In 2002 and 2003, there were 111 heat-stress days from March to October. Moose survival in subsequent winters was below 80 percent. During the same period in 2006 there were 125 heat-stress days, and moose winter survival dropped to nearly 70 percent.
Lenarz stresses that six years of research on radio-collared moose "is at the low end of having enough data for analysis." But he notes that heat stress in domestic cattle, ungulate cousins of moose, has been shown to cause impaired immune systems. And he suspects that moose weakened by hot summers and warm winters may be more susceptible to parasites and diseases that might not normally kill healthy moose.
DNR wildlife researcher Mark Lenarz and Fond du Lac Band wildlife biologist Mike Schrage are co-leaders on the research study of radio-collared moose, but they have differing opinions about whether a booming deer herd in northern Minnesota is hurting the moose population.
"It's easy to hypothesize that more deer mean fewer moose, but that certainly hasn't been the case in Maine," Lenarz says. "They continue to have high moose numbers despite a high density of deer." Lenarz notes that brainworm has been detected in only a few of the necropsies in the study and that blood tests have indicated that only about 18 percent of the radio-collared moose have shown signs of the parasite.
Schrage, on the other hand, thinks that brainworm has been prevalent, though undiagnosed, in the study's mystery moose deaths. And deer are parasite hosts for the brainworm.
"Deer aren't migrating away from the moose range in winter, because of deer feeding and warmer winters. So there is more exposure between the two, more opportunities for parasite transmission," says Schrage. "A growing deer herd on top of that is not a good thing for moose."
Tom Rusch, DNR area wildlife manager in Tower, has likewise noticed hotter weather and fewer moose. And he thinks habitat can help moose out.
"I think there's a general downward slope in the moose population at the western end of their primary range [in northeastern Minnesota], but where they're hanging on in the southwestern extent of that range, there are large conifer bogs that provide summer thermal cover," Rusch says. "I think we need to have a better sense of forest history, of the environment in which moose evolved. We need to try to mimic the natural forest composition that was created by fires, windstorms, and other forest disturbances."
To that end, Rusch has dedicated some of his wildlife management budget to helping fund prescribed burns by the U.S. Forest Service in the Boundary Waters Canoe Area. Like Ingebrigtsen in Grand Marais, Rusch is also favoring conifers in land management -- especially mixed stands of fir, spruce, and cedar that he believes are a critical component of boreal forest moose habitat.
Habitat will be a new focus for the next phase of the moose study, which continues this year with 34 additional radio-collared moose, thanks to a grant from the U.S. Fish and Wildlife Service. Weather gauges are being placed in the forest around Isabella this summer to record temperature and humidity. The gauges will monitor whether certain microclimates exist within the study area, places which tend to stay cooler during hot summer days. The resulting data could help wildlife managers and foresters determine which kinds of habitat provide the best thermal cover, and then try to replicate and expand thermal coverage for moose.
"Habitat is not the biggest problem for moose right now, but habitat can definitely be part of the long-term solution," says Schrage, the Fond du Lac Band wildlife biologist. "Looking five, 10, 20 years down the road, in the face of climate change, wildlife managers are going to be challenged to keep moose on the landscape.
"Some folks have already given up on moose. I think we can keep them around. But we'll need the best information about mortality and habitat use. And we'll need to be proactive in managing for moose. And we'll need funding for all this. So most important, we need the public to stand up and say that it is unacceptable for moose to disappear."
Despite the relatively recent downturn in the moose population, Lenarz of the DNR says that Minnesota's herd of about 8,000 moose is probably still near the high end of where it's been for the last century. After European settlement, he says moose only survived in a few refuges along the Canadian border. Population estimates in the 1930s, though calculated by unreliable means, wagered that 3,000 moose lived in Minnesota; in the 1950s the population was believed to be fewer than 500. Only during the past 50 years, Lenarz says, have moose expanded their range in Minnesota, probably peaking in the late 1980s or early 1990s before the current slow decline.
Driving back down the Gunflint Trail after visiting with lodge owners, I round a bend and a cow moose prances out of dense balsam firs like a mare out of the gate. She stands in the middle of the road and regards me for a moment. The high-noon sun highlights the cinnamon sheen of her spring coat. Then with a high-stepping gait, she's gone.
"Yes," I say to myself and smile. "There's moose in these north woods yet."
Minnesotans may wonder why there is a hunting season on a shrinking moose herd. Wildlife experts say the current regulated harvest does not hurt the moose population.
"It's less than 5 percent of the population, and it's only bulls," says DNR area wildlife manager Tom Rusch. "There are still plenty of bulls to breed all cows."
Mike Schrage, Fond du Lac Band wildlife biologist, agrees: "We could completely halt hunting, and it would not affect the outcome for moose at all."