MINNEAPOLIS — Wildlife biologists trying to find answers about northeastern Minnesota’s declining moose population were dismayed at how many mothers would abandon their calves shortly after researchers attached GPS tracking collars to the newborns. They’re now cautiously hopeful that they’ve found a solution.

Department of Natural Resources researchers started attaching GPS collars to adult moose early last year. The collars gave them regular updates that made it possible to tell when the females were about to give birth. Biologists would give the mother and its calf or twins at least 36 to 48 hours to bond, then swoop in by helicopter to collar the calves and perform health checks. That approach has worked well in Alaska and elsewhere.

But in Minnesota, seven of 31 mothers either never returned or came back but didn’t stay long last spring. So the head of the DNR’s moose calf mortality project, Glenn DelGiudice, and his team consulted specialists around the world.

“The advice we got was lose the helicopter,” DelGiudice said Friday from his field station near Ely.

The abandonments came as a surprise to moose researchers, said Ron Moen of the Natural Resources Research Institute at the University of Minnesota Duluth.

“Nobody wants something like that to happen,” Moen said.

DelGiudice’s team came up with a new approach: approach quietly on foot and limit contact to just four minutes per calf with fewer health checks. By May 15 they had collared 12 calves from nine mothers. But it wasn’t long before five of those mothers abandoned seven calves.

“We’re like, ‘What the heck is going on?”’ he said.

At least the researchers this time were able to capture six of those abandoned calves and send them to the Minnesota Zoo, he said.

DelGiudice said he came close to stopping the study right then. Instead they devised another approach: send in a two-person team just long enough to slip on a collar. They first tried it May 21.

“We’re in there for 15 seconds and we get out right away. … It works beautifully,” he said.

The team had collared 10 more calves from eight mothers with no collaring abandonments as of Friday.

DelGiudice stressed that they don’t know for certain that collaring caused all the abandonments. Mothers will leave unhealthy newborns behind or abandon a calf or if the adult has its own health problems, he said. And it’s also possible that some calves counted as abandoned were actually killed by wolves or bears.

Calf mortality is already high among northeastern Minnesota’s moose. It’s seen as one reason the population has dropped from an estimated 8,840 in 2006 to an estimated 4,350 this past winter. Scientists suspect some combination of warmer weather, parasites, diseases and changing habitat.

Capturing and collaring moose is essential to getting answers, he said. They don’t feel good about the abandonments but it’s a necessary risk, he said.

On the positive side, DelGiudice said, 24 of the 31 mothers approached last year did not abandon their calves, so 40 of the 49 calves survived the collaring process and 34 remain alive. Thirteen born this spring are alive, too, giving researchers 47 young moose to continue to study. He said that’s important because they need several years of data.

Researchers hope to collar 50 to 60 calves using the new technique next year, he added.