REGIONAL—Slightly higher than normal adult moose mortality combined with a low survival rate by moose calves is likely to make recovery of northeastern Minnesota’s moose population “very …
REGIONAL—Slightly higher than normal adult moose mortality combined with a low survival rate by moose calves is likely to make recovery of northeastern Minnesota’s moose population “very difficult”. That’s the conclusion of Glenn DelGuidice, one of the lead researchers in the ongoing studies on moose mortality by the Department of Natural Resources.
DelGuidice offered his comments in an update of the research released this week, and it’s one of the clearest statements DNR researchers have offered, to date, that the region’s wolf population may be playing a significant role in the moose decline.
While adult moose die from a number of causes—including parasites and other health factors, as well as wolf predation— the DNR study has confirmed that wolves are responsible for at least two-thirds of moose calf deaths in northeastern Minnesota. Based on the study’s data so far, a moose calf has a 50.2 percent probability of dying in a wolf attack in northeastern Minnesota. Black bears accounted for another 16 percent of calf deaths, although calves appear to be vulnerable to bear attack primarily in their first couple months. During the course of the study, just under a third of moose calves survived well into their first winter. That is significantly lower than calf survival in many other parts of North American moose range, particularly in the eastern part of North America, where wolf populations are limited or non-existent.
A 2010 study in central Ontario, for example, found that two-thirds of calves in Algonquin Provincial Park and a nearby study area survived their first year. In that study, predators killed only 13 of 85 calves in the study population, with bears and wolves taking roughly equal numbers.
A 2015 moose assessment from New Hampshire reported a 45 percent calf survival rate in one study and 71 percent survival in a second study. Predation was limited to black bears since New Hampshire has no wolf population. Researchers note that moose calves are typically only vulnerable to black bears for their first two months of life. After that, calves are typically large enough and strong enough to outrun a bear. Wolves, meanwhile, remain a significant threat throughout the life of a moose.
Indeed, wolves also cause about one-third of adult moose mortality, and appear to be the indirect cause for a number of additional moose deaths due to bacterial infection.
Over the first four years of the five-year Minnesota study, adult moose survival averaged 85 percent annually, which is a higher rate of annual mortality (15 percent) than the North American average of 8-12 percent.
At the same time, the study found that the overall reproductive potential of the region’s moose population was fairly robust, with pregnancy rates among cows running at about 85 percent, or right around the North American average. “However, as mortality of adult (reproductive) females remains relatively high, it will continue to negatively impact annual calf production,” stated DelGuidice in his latest report. “That, and low survival of calves to one year of age, primarily due to wolf predation during their first 30 to 50 days of life, will make it very difficult for the population’s performance (growth rate) to support increasing numbers of moose into the future.”
It’s worth noting that high wolf densities in northeastern Minnesota are likely contributing to the higher mortality rate for cow moose, which are typically more vulnerable to wolf predation than larger bulls.
The latest results from Minnesota come at a time when the moose population in the northeast appears to have stabilized but shows no sign of recovery after a significant decline beginning in 2006. The DNR has pegged the region’s moose population at around 4,000 the past few years, which represents a 50 percent decline from peaks in the early 2000s.
The DNR’s study has been hampered in recent years by a diminishing number of collared moose. During the first three years of the study, capture crews were able to collar a total of 173 adult moose for the study, but Gov. Mark Dayton suspended the collaring after the 2015 season due to concerns about the high number of moose deaths, particularly among calves, due to the stress of the collaring itself. About seven percent of adult moose died in the immediate aftermath of collaring, although the rate of calf deaths was much higher, mostly as a result of abandonment.
Since then, DNR researchers have relied on the initial group of collared adults to determine causes of mortality in hopes of understanding the factors behind the decline in moose numbers in northeastern Minnesota. And the number of collared adults has fallen dramatically, to just 28 as of this week, mostly as a result of dead batteries and other technical malfunctions on the tracking collars, and mortality.
“Collar failures have really depleted our sample size and have been very disappointing for us, given the enormity of this project,” stated DNR researcher Michelle Carstensen in an update on the study released this past week.
So far in 2017, adult moose survival has been strong, noted Carstensen. In the past six months, only three of the remaining collared moose have died, raising the total number of moose deaths to date to 57 over the four and half years of the study.