Warmer temperatures may be the cause of declining moose populations in northeast Minnesota.
A model by the Minnesota Department of Natural Resources shows moose numbers dropping by 15 percent each year over the long-term, according to an aerial survey.
The agency estimates that there were 7,600 moose in January 2009. That number dropped to 5,500 this year.
There are also fewer baby moose — numbers fell to a record low of 28 calves per 100 cows. Ontario is experiencing a similar decline in reproduction rates, according to the province’s Ministry of Natural Resources.
Minnesota moose are dying for a number of reasons, said Mark Lenarz, group leader for the department in Grand Rapids, Minn.
The ultimate cause is climate change, but parasites and collisions with vehicles are also killing off individual animals. Nearly 70 percent of 150 adult moose with radio collars have died since 2002 because of diseases and parasites, according the department.
The most common parasite is brain worm, Lenarz said. Virtually all white-tailed deer carry the long, threadlike worm.
“It does not affect deer, but it’s invariably fatal to moose,” he said.
Winter ticks, which attach to moose and feed from their blood, are found throughout Minnesota, Ontario, Alberta and Manitoba. Lenarz found one animal infested with more than 70,000 to 80,000 ticks.
“Needless to say, it’s very irritating,” he said. “Moose tend to rub up against tree and rocks in attempt to dislodge ticks. Consequently, they rub off extensive areas of hair.”
Some moose lose up to 80 percent of their body hair. Death can result from loss of blood or insulation, Lenarz said.
Moose mortality is also caused in part by collisions with vehicles and wolf predation. In Minnesota, approximately 15 percent of 150 collared moose died from fender benders since 2002, according to the department.
Six deaths were the result of wolf attacks in northeast Minnesota.
The opposite is true in Michigan’s Upper Peninsula, where moose have increased slowly due to wolf predation. That’s because the wolves keep deer populations low; thus reducing the chance for moose to contract deadly parasites.
See more below this video from Mike Wendland’s blog for the Detroit Free Press.
“Wolf predation is a very effective control on deer density in such deep snow areas, so essentially there is a deer-free area in winter where moose density is highest,” said Rolf Peterson, wildlife ecology research professor at Michigan Technological University, in an e-mail. “It is possible that this reduces the rate at which moose acquire brain worm, which most moose biologists think is an important reason for the moose decline in Minnesota.”
Moose were re-introduced to Michigan in 1985 and now number in the hundreds, Peterson said.
Peterson studies the wolves and moose on Isle Royale and published a book on the relationship. He’s also chair of the Minnesota Moose Advisory Committee.
The ultimate cause of moose decline in northeast Minnesota is climate change, Lenarz said.
Moose aren’t adapted to warm weather and prefer the cold.
When temperatures exceed 57 degrees in the summer and 23 degrees in the winter, moose have to increase their metabolic rate, Lenarz said. This impairs the animal’s immune system and increases its respiration rate.
“Warmer temperatures from climate change are making ideal conditions for diseases and parasites to become fatal to moose,” he said.
Lenarz isn’t sure what will happen to Minnesota moose. Peterson expects deer populations to increase if moose levels get too low.
The species will likely persist in the foreseeable future, according to a report by the Moose Advisory committee. But monitoring is critical.
The Minnesota Department of Natural Resources conducts aerial surveys every January to observe moose numbers and uses models to estimate the entire population.
The committee also makes yearly recommendations, like keeping white-tailed deer populations low to reduce parasite-related deaths.
“At this point, all we can do it watch,” Lenarz said. “We can manage habitat to make sure we’re not losing it. That may simply delay declining populations.
“There’s no way we can control climate, so there’s not an awful lot we can do,” he said.
*Updated for accuracy 3/16/2010 at 3:25 p.m.