Minnesota’s leading moose researchers have one last chance to get it right.

Next month, for the third time, they will try to put tracking collars on about 50 newborn calves in one of the most comprehensive studies ever conducted to find out why moose are in such perilous decline in Minnesota. But the calves’ mothers have abandoned those babies at painfully high rates, creating an ethical dilemma for the researchers and the state’s elected leaders.

About a fourth of the 75 newborn calves collared so far have been left behind by their mothers, a rate that has confounded the scientists. Now they say that neither they nor the public can tolerate another spring in which human interference results in too many newborn calves that either starve or wind up in zoos after frantic rescue efforts in the woods. Nor do they want their ambitious scientific study to be as cruel as nature itself — or to be seen by the public as making the moose problems worse.

Gov. Mark Dayton agrees. On Friday his office said that, if humans are now the second-leading cause of death for collared calves, the additional risks to them aren’t worth the potential scientific gains. He has told the DNR that this spring’s calf collaring with be the last. And researchers say that even this next round will be cut short if calf deaths are too high.

“No abandonments is unrealistic,” said Glenn DelGiudice, the lead calf study researcher for the Minnesota Department of Natural Resources (DNR). It’s a common problem when humans handle some species of wildlife. The question, he said, is how many are “worth what we are learning?”

Because moose, that beloved symbol of the North Woods, are in big trouble. They’ve disappeared entirely in the northwest corner of Minnesota, and in the northeast corner of the state their numbers have dropped by more than half in the last decade, down to only 3,450. The state has embarked on a $1.7 million, long-term research project of both adult and newborns to try to figure out why, and what might be done to save them.

Why do calves die?

A major piece of the puzzle is understanding why so few calves in Minnesota make it through the first year of life. Using sophisticated GPS tracking collars on adult females and their calves, scientists want to find out how they fare, and what kills 70 percent of the young ones before they make it to their first winter.

In the first year of their study, however, the researchers were stunned when 11 out of 49 newborns died as a result of the collaring itself — nine of them because they were abandoned by their mothers.

One, found by the side of a road, was reunited with its mother, one was euthanized with a bullet, and seven died on their own. The grim tally led to some painful soul-searching within the agency and some intense debates about whether they should have had a calf rescue plan in place.

A DNR scientist who was part of the project and who has since left the agency was especially sharp in her criticisms.

“Every research project has to have a plan to deal with the worst thing that can happen,” said Erika Butler, a veterinarian who was part of the project the first year and who examined the bodies of starved calves in her lab. “We had no plan to deal with abandonments that we knew were possible.”

DelGiudice agreed that was a mistake, but said it was often difficult to determine that a calf had been abandoned by its mother until too late.

Last year they did have a rescue plan. In addition, researchers rubbed their clothes in dirt and leaves, used scent blockers and gave up the noisy helicopters that would keep them safe from charging mothers.

Still the problem got worse. Nine out of 25 collared calves were abandoned by their mothers in the first two weeks of May. After a seven-day halt to redesign their approach, researchers cut collaring teams down to two people, and kept the calf contact time to 60 seconds. It may have helped: In the second half of the month, two out of 11 calves were abandoned, and they were a set of twins born to the same cow.

The best news, said DelGiudice, is that seven of the calves abandoned in 2014 were successfully delivered to safekeeping, one at a private animal facility and six to the Minnesota Zoo, where they are now healthy young yearlings on display to the public.

Now the scientists are hoping that they’ve found the right approach to safely collar the calves. And they know they are in the spotlight.

Susan Thornton, executive director of the Legislative-Citizen Commission on Minnesota Resources that has provided $600,000 in lottery funds to pay for the calf project this year, said she’s had a few letters of concern from the public.

“My antennae are out,” she said.

DelGiudice said the DNR has now established a strict limit on the loss of calves this spring. They’ll stop if up to six calves are abandoned because that’s how many zoos have said they will take, or if three calves die as a result of collaring.

“That’s our ceiling,” he said.

There is no magic number. Biologists elsewhere who do similar collaring research say that what’s acceptable can depend on the species — caribou, for one, seem less inclined than moose to abandon their young when under stress. It also depends on the health of a population balanced by what the research can do for it, they said.

“There is not a one-size-fits-all threshold,” said Brent Patterson, a biologist who has studied moose in Ontario.

Searching for answers

But there is clearly something amiss with Minnesota moose because, compared to cows in some places that fiercely defend their young, they are extraordinarily skittish. Maybe it’s because, as their population decline suggests, they are sick, researchers said. Maybe it’s because, in contrast to Alaska, for example, there aren’t as many predators to make them fierce.

Or it may be, said DelGiudice that the collars’ hourly location data and mortality signals allows scientists to see what is normally hidden from humans — a high rate of abandonment by cows.

As for the rest of the calves who were not abandoned — most of them didn’t make it through the first year. Only 10 out of 34 calves that were successfully collared in 2013 survived through winter. The rest were either killed by wolves and bears, slipped through the ice and drowned, or were abandoned by their mothers later in the season. The following year the study was hampered by another problem — the collars fell off nine calves, leaving only six that could be followed. They, too, died from predators. And DelGiudice and his fellow researchers have spent the winter testing collar durability, in part by trying them out on beef calves.

But 70 percent calf mortality rate is too high to maintain a viable moose population. They need at last half of their offspring to make it through the first year to maintain their numbers.

The results of a parallel collaring research project for adult moose show they, too, are struggling with predators, diseases and parasites that kill them at a rate that’s too high to sustain the population. In 2013, a fifth of them died — twice the rate of other moose populations. The second year only 11 percent died.

For a population that is under such pressure, every additional year of research produces a treasure trove of data, said Ron Moen, a biologist at the University of Minnesota Duluth who is studying moose habitat and forage.

“We had two springs that were really late,” he said. “Now we have a really early spring and the cows will [be] in better condition.”

That means, he said, that cows may do a better job of defending their young against predators.

And, perhaps, the scientists.