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A Talk on the Wild Side.

Minnesota: Warmer Temperatures Take a Toll on Minnesota Moose

A bull moose emerging from a freshwater bath
Video iconVideo: To determine how warming temperatures impact moose populations, scientists capture and study the animals, which can reach 7 feet and weigh more than 1,000 pounds. Watch this video to see one of the ways this data is collected.

Minnesota’s iconic moose might be the seven-foot-tall, 1,000 pound version of the canary in the coal mine. The large antlered animal appears on the verge of being pushed out of its southernmost historic range by climate change and other stressors.

Biologists at Agassiz National Wildlife Refuge and the Minnesota Department of Natural Resources say rising temperatures are at least partly to blame for a sharp drop in moose numbers in northwest Minnesota since the early 1990s.  Warming appears to make moose more susceptible to deer-borne parasites and ticks, which often lead to malnutrition and death.

According to aerial winter surveys conducted by the state, northwestern Minnesota’s moose population has dropped from a high of about 4,000 in the early 1980s to fewer than 100 in 2007.  Agassiz Refuge used to boast more than 430 moose; now, it has fewer than 50. 

“For years, Agassiz Refuge was the place to go if you wanted to see moose year-round,” says Agassiz Refuge Manager Maggie Anderson. “Our entrance signs and all of our brochures featured the moose as the emblem of the refuge.” Then, she laments, “in 1995, that all started to change.” These days, moose are rarely seen.

A bull moose bathes

A bull moose creates a distinctive silhouette. Heat stress and malnutrition are causing a sharp drop in moose numbers in the northwestern corner of Minnesota. Photo: USFWS. Download.

Beginning a century ago, moose habitat in northwest Minnesota changed dramatically with human settlement. Old-growth forest was logged and wetlands drained for farmland. Moose —the name means “twig eater” in Algonquin — adapted as best they could.  

“I’ve seen moose in cropland, eating alfalfa on their knees,” says Anderson. “When you are on the southern edge of moose range and things change even just a little bit,” she says, “it can be enough to tip a population. In our case, [warming] has been the straw that broke the moose’s back.”

Average winter temperatures near Agassiz Refuge have risen by about 12 degrees Fahrenheit over the last 41 years; summer temperatures have increased by about four degrees. Moose calf counts declined the year after higher mean temperatures were recorded.

Moose expend added energy when temperatures in March (two months before calving) exceed 23 degrees and temperatures in September breeding season exceed 57 degrees. Since 1984, temperatures have passed those thresholds more times than they did in the previous 24 years. 

A helicopter follows two moose across snowy terrain
Biologists fire a net gun from a helicopter to capture a moose briefly for study and health testing. Climate change has contributed to the sharp drop in moose numbers in in northwestern Minnesota, say scientists. Photo by Clint Austin/Duluth News Tribune. Download.

In addition to capturing and studying wild moose, researchers consult studies of cattle, mooses’ closest domestic counterparts. Like moose, cattle are ruminants — mammals that pre-digest food in the first part of their four-section stomach. Studies show that “cattle exposed to higher temperatures have an impaired immune system,” says Mark Lenarz, who leads forest wildlife research for the Minnesota Department of Natural Resources. If moose react the same way, he says, “higher temperature would make them more vulnerable to diseases and parasites.”

Moose study area is in northwestern Minnesota
Study area. Credit: USFWS.

Heat-stressed moose are more apt to become malnourished and have lower reproductive rates. Scientists speculate that reproductive rates may also be impaired by copper deficiency, exacerbated by increased particulate absorption in soil and vegetation.  The problems of heat stress and malnutrition compound one another.

The moose research project linking rising temperatures to moose decline was funded in part through the Adopt-A-Moose Program at Agassiz Refuge. The program stopped in 1999, but the supporting website still hosts useful information and photos. 


Climate Change Focus: Adaptation

Author:  Tina Shaw, Midwest Region External Affairs Office, 612-713-5331, Tina_Shaw@fws.gov

Contact:  Chuck Traxler, 612-713-5313, Charles_traxler@fws.gov 

Related Websites: 

I wonder if it has anything to do with a huge increase in the numbers of a certain predator that eats about 10 moose per year. Three to seven hundred in the early 80s to 3000 now. At ten moose per predator that would be a lot less moose.
# Posted By somsai | 5/20/11 10:59 PM

No mortality factor operates in a vacuum...so wolves certainly play a role...though there are moose declines noted elsewhere w/out wolf presence.
# Posted By | 5/21/11 11:24 PM

Thanks for your question. According to Agassiz NWR Manager Maggie Anderson predation is not a factor in the Minnesota moose population decline. Researchers investigated all collared moose that died during the study and the cause of death for most of the moose was malnutrition, a side effect of the parasites. Malnutrition that leads to death and/or lower birth rates are the cause of the population decline. While predation is certainly part of the natural cycle here in northwestern MN, it is not enough to impact the entire moose population.

Agassiz NWR does have two wolf packs, each pack has 5-7 wolves. During research on Agassiz NWR's wolves conducted from 1997-1999, it was found that 13 percent of their diet consisted of moose, compared to nearly 40 percent deer. Similar to what was observed during the late 1990s moose study, we observe very little direct predation of wolves on moose.
# Posted By Chuck Traxler, USFWS | 5/23/11 2:16 PM
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