The mysterious screeching coming from the woods was unlike anything the moose researchers had ever heard.
Shuffling through the snow, they edged closer to the sound and spotted a weak and distraught moose.
“It was grinding its teeth,’’ said Erika Butler, Department of Natural Resources wildlife veterinarian. “Cattle and horses do that when they are in extreme pain.’’
The researchers euthanized the dying moose and determined it was severely infected with brainworm. They hadn’t stumbled on the animal by accident. It was one of 111 moose captured this winter and fitted with unique GPS-equipped radio collars, so they can be located, and electronics that alert researchers if a moose is immobile for a long period, indicating death or near-death.
“Our collar went into mortality mode and sent us a text message,’’ Butler said. “We were able to get out there and find it [before it died]. It’s awesome technology.’’
Researchers hope that technology will unravel the mystery of why Minnesota’s moose population is plummeting — half the herd has died off in just two years. The population, now estimated at 2,760, is down from 8,840 as recently as 2006. Wildlife officials say that at that rate they could be gone from the state in a matter of years.
So far, only eight of the study moose have died, and four of those deaths were blamed on the capture process, in which the moose were sedated.
“We think it was due to the very poor condition the animals were in,’’ Butler said.
Of the four other moose, one was the animal found with brainworm, two were killed by wolves and a third died after a wolf bite became infected — another unique observation credited to the technology. Researchers got to the animal before wolves did.
“We found it got a bacterial infection from the wolf bite, and spread,’’ Butler said.
Though wolves were responsible for three of the four moose deaths, Butler said it’s too early to draw any conclusions.
“This is the time of year we’d expect to see wolves take moose,’’ she said. Moose are weakened from a long winter with little food and are most vulnerable to predation, she said. “They’re living off fat reserves.’’
Researchers don’t believe wolves are responsible for the moose population decline, despite such claims by some residents.
“We believe it’s health-related,’’ Butler said. “We’re seeing prime-age animals dying, which isn’t normal when you look at other moose populations. We’re also seeing them dying in seasons they shouldn’t be — June, July, August and September. Other moose populations do really well at that time.’’
Ironically, the researchers need more of the collared moose to die so they can determine the causes.
A second phase of the first-of-its-kind study will begin next month when researchers, using a helicopter, locate 50 of the radio-collared moose, which were pregnant when captured, and put radio collars on their newborn calves to study calf mortality. Calves are vulnerable to wolves, black bears and other predators, and that part of the study will help researchers understand how calf mortality might be impacting the population.
Still, it’s the death of adult moose that is most puzzling.
Some have theorized that eastern equine encephalitis, which was first found in 2007 in northeast Minnesota moose and which is lethal in horses, could be a smoking gun. It is spread by mosquitoes, which get it from birds, not horses, Butler said. “When horses get it, they usually don’t have enough of it in their blood to infect another mosquito. They usually die quickly. We call them dead-end hosts.’’
Butler said researchers aren’t sure what impact, if any, the disease is having on moose, but the study should reveal that.
Another theory is that increases of sulfur and mercury in the environment could be to blame. High sulfur levels can cause polioencephalomalacia (PEM), which causes death. But Butler said no Minnesota moose have been found with PEM or high mercury levels.
Brainworm remains a better possibility. Deer carry it (and are unaffected by it), and slugs and terrestrial land snails spread it. And it’s deadly to moose. Some wonder if the relatively high densities of deer in northern Minnesota could be contributing to the problem.
Though hunting mortality wasn’t considered a factor in the population drop, officials in February suspended future hunts indefinitely.
Butler believes the study will solve the moose mystery, though it could be a year or two before answers are revealed. But even if the problem is identified, the question is whether officials will be able to do anything about it. Inoculating moose from disease isn’t practical.
Meanwhile, there’s still snow in the northern Minnesota woods, which could help moose. Winter ticks, which infest moose and can kill them, fall off now to lay eggs.
“If they drop off in snow, much fewer of them survive,’’ Butler said.