Minnesota wildlife researchers say they are getting a better understanding of what's killing the state's moose and causing a major population decline.

After three years of monitoring live adult moose via satellite, retrieving them as soon after death as possible and carefully examining their remains, wildlife biologists can identify specific causes of death, reported Glenn DelGiudice, Minnesota Department of Natural Resources moose project leader.

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Preliminary results from 47 of the adult moose captured and collared during the past three years show that two-thirds died from health-related causes including brainworm, winter ticks, bacterial infections, liver flukes and severe undernutrition, DelGiudice reported. Wolves killed one-third of those moose but sickness in 25 percent of those animals made them easy prey, he said.

"I think the DNR has come a long way in three years and done a good job of answering a lot of the unknowns we had from some earlier moose studies and what the causes of mortality are," said Mike Schrage, wildlife biologist for the Fond du Lac Band of Lake Superior Chippewa, which has been involved in much of Minnesota's moose research. "I think they've done a good job of getting at some of the interplay between health issues and wolf predation."

Of particular interest is how winter nutrition in moose affects their health, DelGiudice said. When moose are heat-stressed in winter they aren't getting enough food and eventually succumb to health problems, weakness or wolves.

"It's incredible how it's tracking," he said. "The heat stress index of moose is tracking very closely with the severity of winter nutrition of these moose. What it's saying is that winter nutrition could be a key to this."

That information is based on moose urine samples the DNR has gathered from the snowpack, DelGiudice said.

In summer, he said, moose can go to ponds or streams to cool down when they get too warm. In winter, moose can only lie in the snow and shade, which offers less cooling, DelGiudice said. When air temperatures reach 23 degrees in winter, he said, moose can begin to experience heat stress, increasing their metabolism, heart rates and respiration.

"If the effects of climate change are negatively affecting the nutrition of moose in winter, it could clearly make them compromised and more vulnerable to disease and other things," he said.

Fond du Lac's Schrage finds the correlation between winter temperature and moose nutrition significant.

"We've been saying for a number of years that we've previously found relationships between warm temperatures, particularly in winter, and subsequent moose mortality," Schrage said. "Glenn's work would appear to back that up and show how that happens."

Data that DNR researchers have collected to date is far from conclusive, DelGiudice said.

"Only more data on moose deaths collected over a longer period of time will determine whether the trends researchers are seeing continue," the DNR's moose update on its website stated.

DelGiudice said a minimum of six years of data will be necessary for a valid study.

"But we know we can't wait to start making some preliminary recommendations after three years of preliminary findings," DelGiudice said.

Moose for the most part disappeared from Northwestern MInnesota in the 1990s and their numbers have been crashing in the Northeast for the past decade.

In Northeastern Minnesota, moose numbers have dropped from about 8,500 moose as recently as 2006 to about 3,500 last year. The results of this winter's annual aerial survey of moose areas will be released in coming months.