This past winter, researchers attached high-tech GPS collars to more than 100 adult moose.

Biologists have begun collaring moose calves in the second phase of an ambitious study to determine why Minnesota's moose population is declining so rapidly.

This past winter, researchers attached high-tech GPS collars to more than 100 adult moose. They started putting collars on baby moose last week and are about halfway to their goal of 50, Minnesota Public Radio reported Thursday ( ).

Soon after a female gives birth, wildlife handlers collar the newborn. said Glenn DelGiudice, a biologist with the Minnesota Department of Natural Resources

"Most of the time, they're able to just walk up to the calves, they're anywhere from ... maybe four- to five-days old. They're pretty stationary still; they don't move around much yet," he said. "They slip a GPS collar on them, ear tags, take a rectal temperature, a body weight, and maybe a hind foot length, to get an assessment of their development and condition, and they're pretty much done within about five minutes."

Three collared calves already have died, one shortly after being collared, and two after being abandoned by their mothers. In the adult study last winter, four died after being tranquilized and collared.

DelGiudice said the risks are worth it because there's a "very good chance" northeastern Minnesota's moose will be gone in 20 years or less if the state just lets nature take its course.

The collars allow researchers to track the calves and adult moose on computers. Researchers aim to quickly get to a dying animal to try to learn why they died.

"When that collar kicks into mortality mode, and that happens when the calf is not moving very much, it sends us a text message and an email," DelGiudice. "And then, very similar to the adult study, we can mobilize our team to go into the field and investigate and get that carcass, hopefully before it's scavenged or decomposed."

The moose population in northeastern Minnesota has declined by two-thirds since 2006, to an estimated 2,760 this past winter, according to the latest population survey. It's still unclear why. Scientists suspect some combination of higher temperatures, parasites, diseases, contact with deer and changes in habitat.

Ron Moen, a biologist at the University of Minnesota Duluth, said it's normal for about half of moose calves to die in their first year. But in the past six to eight years, between 60 and 80 percent have not survived their first winter, he said.

The calf study already has provided some surprises. DelGiudice said one female moved 3 to 4 kilometers away from its calf after it was handled and was gone for a couple days. He said they were sure it was abandonment. But the next morning, when he checked his computer, he found the mother back with the calf.

"And they've been together since and doing just fine, so you never know," he said. "We're learning things about their calving behavior and movements that most biologists in North America don't know, because they haven't had the technology."