Minnesota’s calf moose perishing at unusually high rate
Minnesota’s dwindling moose herd has a year off from human hunters in 2013, but that doesn’t mean life for the big north woods critters is a walk in the park.
Moose are still being hit hard by disease, injury and parasites, and they are still prey for four-legged hunters that don’t need licenses.
And there are still far more dying than should be.
Researchers studying calf moose in Northeastern Minnesota have so far found more than two-thirds of the young moose died during their first four months of life, leaving far fewer young moose than needed to sustain a healthy population.
Of 49 calves fitted with GPS-transmitting collars in May, just days after they were born, 11 died from complications immediately after the capture. Most of those were caused by the cows abandoning their calves, not from stress or harm. Four other calves slipped out of their collars, said Glen DelGiudice, lead moose researcher for the Minnesota Department of Natural Resources.
Of the remaining 34 calves being tracked in the study, 24 already have perished in less than four months, a 71 percent mortality rate that has researchers shaking their heads.
On average, in studies worldwide where predators are present, about
55 percent of calf moose die in their first full year.
“It varies a lot based on the predator-to-prey ratio … but we would hope to have about a 45 percent calf (survival) rate after one year,” DelGiudice told the News Tribune.
“The very rough estimate in Minnesota is that we have been down to about 28 percent survival in recent years. But we still have seven months to go and we’re already there. That’s not good.”
DelGiudice said he can’t even guess how many of the 10 remaining collared calves might survive the first full year.
Predators have been the leading cause of death for moose calves. Bears killed 4 of the 24, most in the first few days after birth, and wolves have taken 16 calves. One calf drowned, two were abandoned later by their mother and one died from unknown causes.
“They are just very vulnerable the first few days and weeks. Since then, the mortality rate has been slowing … but we are still losing them,” DelGiudice said, noting there has been one calf killed by predators in September. “As they get bigger, their chances get better. But they still have all of winter to get through.”
DelGiudice noted that Minnesota had a thriving moose population 10 to 15 years ago when the state’s moose range had roughly the same number of wolves. Wolves clearly aren’t the cause of the steep decline in moose population, he said. But they may now be helping to push the decline a little faster.
“When we had 9,000 moose and the same number of wolves, the number they took was far less significant and likely not impacting the population,” DelGiudice said. “But with fewer than 3,000 moose now, and roughly the same number of wolves, that predator-to-prey ratio has changed. They (wolves) aren’t the driving factor, but they may be having an impact.”
The GPS study on calves is part of Minnesota’s largest-ever effort to track moose movements and, especially, their deaths. Crews have been swooping in as soon as the GPS tells them a moose has stopped moving, hoping to retrieve the intact body so the precise cause of death can be determined. In addition to DNR crews, U.S. Forest Service and Fond du Lac and Grand Portage band of Ojibwe wildlife crews are helping in the recovery effort.
Researchers hope they can get additional funding to push the studies out to five or seven years total to get a clear sense of what’s killing moose. Still, they concede, even if they find a single cause or combination of causes, they may not be able to solve the problem.
The state DNR and tribal resource agencies have, for the first time in decades, canceled this year’s moose hunt after aerial surveys showed moose numbers had plummeted 35 percent in just one year, with only 2,760 estimated this year, down from 4,230 in 2012. The Northeastern Minnesota population was more than 9,000 as recently as 2006.
Even if calves were surviving at a higher rate, researchers note, too many adult moose have been dying to sustain the population.
The Northeastern Minnesota crash mimics that of Northwestern Minnesota, which saw its moose population decline in the 1990s from about 4,000 animals to just a few dozen. Scientists studying the northwestern moose decline concluded that a warmer climate has compounded multiple other problems, such as disease, malnutrition and parasites.
Adults dying, too
In a separate study of adult moose across Northeastern Minnesota, the bigger animals are faring a little better. So far, 19 of the 107 moose that survived capture and collaring last winter have perished, said Dave Pauly, DNR researcher on the project, for an 18 percent mortality rate.
Of those 19 moose, nine were either injured or killed by wolves, although three of those may have had other issues such as an infection after an attack or a health problem that allowed wolves to catch them. Three had severe winter tick infestations resulting in anemia; one died from brain worm, a parasite spread by deer but not lethal to deer; one died of a broken leg and subsequent infection; and five died from as yet undetermined causes.
The adults were most vulnerable in April and May, after a long winter and before nutritious food began sprouting, when 12 of the 19 adults died. Of those adult moose that have died, four were bulls and 15 were cows. Bulls ranged from 2 to 9 years old; cows were 3 to 14.
Pauly said it’s too early to judge results but that the trend continues to look bleak.
“We have a small sample size at this point, very early in the study, but a 19 percent mortality rate is somewhat higher than expected,” Pauly said.
Mike Schrage, wildlife biologist for the Fond du Lac band’s natural resources department and a longtime moose researcher, said he’s not surprised by the high mortality levels so far, but he cautioned several more years of research are needed to draw conclusions on what’s causing the problem.
“We’ve known from earlier studies back to 2002 that pregnancy rates all along were pretty decent and that most adult cows produced one or more calves each year. We also knew most of those calves disappeared sometime between birth and January when we do the moose counts,” Schrage said, noting radio telemetry work since 2002 also indicated a high adult mortality rate. “While I’m not surprised, at the same time it’s depressing that our moose herd just can’t seem to catch much of a break.”
Schrage and Pauly said the good news is that the system of tracking and finding dead and dying moose using GPS collars with real-time data is working well, allowing crews to get critical tissue samples to a veterinary diagnostic laboratory within a few hours. In the past, the carcass was often destroyed by predators or too decomposed to offer any clues.
“Ultimately it will help us make better decisions about what can or needs to be done if we’re going to try and recover the herd,” Schrage said.
John Myers | Forum News Service