The first year of a landmark study found higher mortality rates than normal and listed several causes. Researchers say more work is needed.
A bull moose, sprouting the bumps of new antler growth on its head, grazed in a swamp off the Gunflint Trail in northeastern Minnesota — possibly one of the lucky ones in a declining population. One season of a high-tech study showed that the adult death rate was 18 percent; for calves, it was 71 percent.
It’s tough to be a moose in Minnesota.
The deaths of 54 that were tracked as part of the biggest and most high-tech research study ever conducted on moose provide a rare glimpse into the harsh life they face in the wild and help explain why they are rapidly disappearing from Minnesota’s North Woods.
By far the greatest number, primarily calves, were killed by bears and wolves. A number were abandoned by their mothers; one drowned. Three adults died from massive infestations of winter ticks, and others succumbed to deer-related parasites and infections.
Researchers said one season’s worth of data from about 150 collared moose is not enough to illuminate trends or to provide solutions in how to help them rebound. But it’s clear, they said, that more are dying than is normal.
Calves suffered a 71 percent mortality rate after only one summer, said Glenn DelGiudice, the wildlife researcher for the Minnesota Department of Natural Resources who is running the calf research portion of the study.
And the ones that made it so far still have to survive their first winter.
Moose need a mortality rate of 50 or 55 percent in the first year of life to maintain their population, DelGiudice said.
The adult death rate was 18 percent, said Michelle Carstensen, who is running the adult research for DNR. If that rises to 30 percent in the winter, as expected, “that’s not sustainable,” she said.
The number of moose in Minnesota plummeted by one-third last year, double the rate of previous years.
Results of the annual aerial moose survey conducted in January indicated that 2,760 moose were left, down from 4,230 in 2012.
In 2006, the population in the northeastern corner of the state peaked at 8,840, but by then moose had already largely disappeared from the northwestern corner of Minnesota, where they had long been part of the landscape.
The sharp decline adds new urgency to the effort to understand why moose are dying in such numbers. So far, the project has been funded for two years with $1.2 million from the state, tribes and the University of Minnesota Duluth.
Now researchers are hoping for another $750,000 from the state in part to determine how much of an impact global warming may have on the moose population.
Researchers want to attach devices on 30 moose that measure ambient and body temperatures to determine whether heat stress from higher average summer temperatures is playing a role in their demise.
A number of other studies have shown a connection, but none actually have provided the biological evidence, DelGiudice said.
103 adult moose collared
In the first year of the study, wildlife crews found and collared 103 adult moose with GPS devices that track their every movement.
When they die, in a wilderness version of the television show “CSI,” a signal alerts crews who rush in and recover the carcass to determine its cause of death. The crews include staff from the DNR, the U.S. Forest Service, and the Fond du Lac and Grand Portage bands of Ojibwe.
In springtime, when the GPS signals alerted the crews that the females were bedding down to give birth, specially trained crews that do the same work in western states and Alaska carefully moved in to collar 50 newborn calves.
Despite taking all the precautions they could think of, one frustrating and unexpected result of the calf collaring is that 11 died, said DelGiudice.
Nine of them were abandoned by their mothers. One died when a mother stepped on it during the attempt to collar it and one died for unknown reasons.
The timidity of the mothers surprised the wildlife experts who have done such collaring elsewhere, DelGiudice said.
In Alaska, the helicopters had to hover directly above the handlers on the ground to keep the mothers at bay. In one case, the pilot had to nudge a mother moose away with the helicopter strut.
“Here the mothers were skittish and would bolt for distances,” DelGiudice said.
In addition to those 11 deaths, four calves slipped their collars, leaving a total of 34 for the researchers to follow. By the end of the summer, 24 of them had died. Four were eaten by bears and another 16 most likely were killed by wolves, though researchers aren’t positive about four of those. One drowned, two were abandoned by their mothers well after being collared and one died for unknown reasons.
If the 10 that are left survive the winter, their chances are good, DelGiudice said.
Easy prey for wolves
Wolves also took about half of the 19 adults — eight were direct kills and two died from infections that developed from wounds, Carstensen said. Three apparently healthy moose died for unknown reasons.
That raises tantalizing questions about the predator deaths. Moose that are sickened or weak are easy prey for wolves, which then eat the evidence of what caused the decline in the first place, she said.
That may be what happened to one moose whose demise, by sheer chance, was witnessed by Amanda McGraw and others in a group of graduate students who were doing moose habitat research near Isabella, Minn., during the first week of September.
They saw an adult moose near the edge of a pond, and moved in to get a closer look and take photos. They crawled through the long grass on their bellies, and only as they got close did they realize that the moose was sick and injured.
It ignored them, and then stumbled into the water, where it couldn’t get up.
They called in the moose wildlife crew and left to finish their work. When the crew arrive two hours later, the moose already had been eaten by wolves that most likely were lurking in a nearby patch of poplars waiting for its collapse.
She realized only later, McGraw said, that while crawling through the grass she might have come nose to nose with a wolf.