Even in the face of a northeastern moose population that’s been on a sharp decline for years, the numbers from the early part of an adult and calf mortality study are sobering.
• 71 percent: the mortality rate of moose calves being studied that have died since May.
• 18 percent: the mortality rate of adult moose collared last winter.
Even with nearly three of four moose calves dying, a moose population could sustain itself – or even grow – if the adults were surviving well. But that’s not what researchers are finding.
“When you have high adult mortality and then also high calf mortality, it just exacerbates the rate of decline,” said Glenn DelGiudice, the DNR lead moose researcher. He’s leading the calf portion of the study.
Said Michelle Carstensen, the DNR wildlife health program leader, who’s leading the adult portion of the study: “I think 18-percent mortality is quite high at this early stage.”
Researchers are in the middle of one of the most intense moose studies ever undertaken, having captured and placed GPS collars on more than 100 adult moose, and nearly 50 calves. The collars relay information to the researchers, whose goal is to reach every dead moose within 24 hours of its death.
They hope that by doing so, they’ll be able to gain a firmer handle on what’s causing the population of the iconic animal to decline. Surveys this year led researchers to estimate there are 2,760 moose in the northeast, which is less than half of the estimated population in 2010.
The population declines led the state and three Indian bands – Bois Forte, Fond du Lac, and Grand Portage – to cancel their moose-hunting seasons this fall.
But even without hunting pressure, moose in the northeast are still having a tough go of it.
The calf mortality has been especially eye-popping. Nine died as a result of capture-related abandonment – their mothers left and didn’t return, or returned and then left again.
“We don’t know why,” said DelGiudice, who noted there’s not a lot of stress on the calves, and that researchers handle them for about four minutes.
Two others died as a result of capture-related mortality, and four slipped out of their collars. That left 34 calves for researchers to study.
Of those 34, wolves killed – or are believed to have killed – 16. Bears killed four; two were abandoned by their mothers; one drowned; and one died of unknown causes.
As of earlier this week, 10 calves remained.
In other studies in which predators such as bears and wolves have been present, between 40 percent and 45 percent of the newborn moose survived a year.
“That’s what we would have hoped and expected,” DelGiudice said.
He has no way of knowing if any of the calves still will be alive next year.
“We can’t really predict how many will make it through the winter,” DelGiudice said.
Adults faring better
Of the 107 adult moose collared last winter and included in the study, 19 have died.
Wolves killed eight of them; wolves injured another two, but secondary infections actually killed them. Winter ticks killed three and unknown causes killed another three. Brainworm killed one. Another had liver flukes, but was killed by a secondary infection, and another had a broken leg and died from an infection.
Of the wolf kills, Carstensen noted: “What that really means is we get there and find wolves killed the animal. It doesn’t mean it was a healthy, robust, prime-of-its-life moose.”
She related the story of a moose that died two weeks ago. A graduate student saw a moose with a collar. She belly-crawled close to the moose, and then stood up. The moose didn’t move, and didn’t really even acknowledge she was there. She called DNR researchers, and then tried to get the moose to move a little bit. It did, and the student noticed the moose had a limp and a wound on its back end.
She left the moose, and researchers arrived two hours later to find the moose had been killed by wolves.
“So that’s a wolf-killed animal, but clearly it had something major going on that predisposed it to predation,” Carstensen said.
She said it’s hard to predict when the next moose will die. In typical systems, early spring and mid- to late winter are the times of peak mortality. But previous research has shown moose in the northeast could die just about anytime.
“I think we’ll have more dead between now and the winter, for sure, but I just can’t predict what the causes are going to be,” Carstensen said.