SUPERIOR NATIONAL FOREST, Minn. -- The moose of Minnesota are dying, and no one knows why. The state lost 50 percent of its moose population since 2010.

Michelle Carstensen of Minnesota's Department of Natural Resources is leading a $1.2 million study.



Michelle Carstensen CBS News

"We used to have two significant moose populations in our state -- one in the northwest, one in the northeast. And the northwest moose population is pretty much gone," Carstensen said.

In the Superior National Forest, where the snow reached four feet deep in places, researchers in helicopters searched for the thousand-pound animals. They braved the harsh winter conditions because the trees are too thick to see the moose in the summer.

CBS News was with them when they spotted a cow and her calf. A shot from a tranquilizer gun brought the female to her knees.

The wind chill fell to as low as 40 below zero -- not exactly ideal laboratory conditions for the researchers, who set the goal of darting the animal, harvesting the samples and getting the moose back on its feet again within 20 minutes.



Researchers set the goal of darting the animal, harvesting the samples and getting the moose back on its feet again within 20 minutes. CBS News

The team worked quickly to take blood and hair samples and install a radio collar and GPS tracker. A tiny transmitter was placed in the moose's throat to record its body temperature.

Even though it's only the second of seven years of research, climate change is a definite suspect. Average winter temperatures in northern Minnesota have increased more than four degrees over the past 40 years. Scientists think warmer winters and longer summers may be weakening the heat-sensitive moose and giving wolves more time to hunt them. Parasites also have more time to infect them.

"So it's kind of a race against time to understand what might be driving this, and even if we can figure that out, having tools on hand to do anything about it is the next challenge," Carstensen said.

The researchers admit they may not come up with answers before all the moose are gone from Minnesota, but what they ultimately learn may save the moose populations in the rest of North America.