It’s getting harder and harder to find moose in the tip of the Arrowhead, although this is still the best habitat the state of Minnesota offers these majestic animals. Over the last 10 years the count has gone from 8,000 to just fewer than 5,000. But why are the moose dying? A cadre of scientists from the Midwest and Ontario are trying to figure out what is causing the drop in moose numbers. Hopefully, before they are all gone.
This is part two in a three-part series that takes a look at the decline in numbers of moose in Minnesota. In the last 10 years moose have been dying at an alarming rate throughout the state, and they have all but disappeared in Northwestern Minnesota. Scientists and wildlife biologists are compiling information that looks at warming temperatures, diet, disease, and predators, and in time the why, or multiple whys, should be known. But whether or not the moose can be saved is another matter.
Wildlife biologists are studying what moose eat—and when they eat to see if that is having an effect on their health. On average, an adult moose needs 9,770 calories per day to maintain to maintain its body weight.
Moose browse on young aspen, paper birch, dogwood, mountain maple, and hazel.
“In the summer they eat aquatic plants and in the winter they add balsam fir to the diet. In Maine, moose browse on broccoli in the farmers’ fields,” said Mike Schrage, wildlife biologist with the Fond du Lac Band.
“Moose nutritional needs vary depending on the time of year and life stage of the animal. Nursing cows and growing calves need extra calories. Bulls need to put more energy towards antler development. Moose and deer actually reduce their metabolic rates in the winter and therefore need to take in fewer calories,” said Schrage, who said he thinks there is adequate food supply for moose most of the year.
In the spring, before snowmelt, moose have often lost their stores of fat and are at their most vulnerable for disease and starvation. And they are very vulnerable to the smallest of predators: winter ticks.
“We counted 30,000 on one animal,” said Erica Butler, wildlife veterinarian, Division of Fish and Wildlife for the State of Minnesota.
“Their hair falls off and they turn white. They get cold and weak, can’t eat and starve to death,” said Butler.
It is a grim picture for an animal so revered in the Northland.
Moose cows are having calves near the normal rate (for moose), said Mark Lenarz, PhD, group leader of the Minnesota Department of Natural Resources (DNR) Forest Wildlife Populations and Research Group.
“We measure pregnancy rate from blood samples taken when moose are captured. Hence we have data from 2002, 2003, 2004, 2005, and 2008 (2010 is still being analyzed).
“Over the five years of data, the average pregnancy rate was 83 percent and ranged from 55 percent to 100 percent. Elsewhere in North America, the average pregnancy rate is 84 percent. Hence, we are close to the average. The subjective condition of these cows (as estimated at capture) spanned a wide range from relatively poor to excellent.”
Calves typically weigh 25 – 35 pounds at birth. Within one week, moose calves can swim and walk. They stay with their mother 12 – 18 months before heading out on their own.
So researchers do not believe low pregnancy rates are a problem here in Northeastern Minnesota. But many calves don’t live to be a year old, and researchers want to know why.
Ron Moen, a research scientist with the Natural Resources Research Institute (NRRI) at the University of Minnesota Duluth, said moose live an average of 15 to 25 years and tend to travel in a range of 3 to 5 miles throughout their lifetime, although some will wander farther.
Predators take some moose, said Schrage. “We can’t forget about black bears—they have been shown in other studies to be an efficient predator of moose calves. I don’t disagree that wolves are having an impact on our moose herd and without wolves, we’d have more moose. However, our moose research to date indicates high adult mortality, primarily due to disease or parasite issues, which is what’s driving our moose herd.
“We’ve demonstrated a correlation between warmer temperatures and subsequent moose mortality. It can be dangerous to infer cause and effect from a correlation, but my belief is warmer temperatures are increasingly stressing our moose herd and making them more susceptible to disease and parasites issues,” said Schrage.
Fish & Wildlife Veterinarian Butler has investigated, “Aapproximately 10 – 20 anecdotal reports of sick moose per year that were reported by the public. For the majority of these we are able to diagnose the cause of death, but there is a huge sightability bias. We can’t apply this data to the population overall. Past studies have shown that the rate of brain worm infection is inflated in sick moose reported by the public.”
At her lab, Butler screens for 27 diseases and viruses. But in 25 percent of the cases, a cause for death can’t be determined, she said. What is driving diseases and how to stop them from spreading might be difficult to ascertain, said Butler.
“What is known,” added Butler, “Is that in the span of a decade the moose herd crashed in Northwestern Minnesota. The moose all but disappeared. In Northeastern Minnesota moose look like they are going the same way. By 2020, your moose population could be gone as well. With losses of 8 to 12 percent a year, the moose will be gone if something doesn’t change.”
Butler said brain worm and liver flukes also contribute to the demise of moose, but judging from her studies, not to the degree that some scientists thought.“In 2008 we collected 87 brains (from hunters, over half from First Nation hunters). Four had lesions that looked like brain worm; nine had chronic inflammation in their brain.
“We also collected 165 livers (from hunters) in two years and tested them for liver flukes. Of those, only six livers were infested more than 50 percent,” Butler said.
The bottom line, said Butler, is that “we know hardly anything about what is killing our moose. We have identified some diseases in our moose (like brain worm) but we have no idea what impact they are having on the population at large. I believe it will be a combination of things, but we will have to wait until our mortality project [slated to begin in January, 2012] to find out,” said Butler.
With antlers that measure up to 5 feet across and weigh as much as 40 pounds, with the ability to run 35 miles per hour, easily swim 10 miles, and walk nimbly and silently through thick brush, Minnesota moose are magnificent creatures, a marvel to look at, but will they still be here in 20 years?
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