Mortality high for moose calves
More than 50 percent of radio-collared calves died in the first few weeks
he life of a moose calf is a tenuous one. That’s one of the findings in the Department of Natural Resources’ ongoing moose study, one of the most far-reaching studies of this northern species ever conducted in the world.
Since early May, researchers, with help from DNR wildlife staff, have been capturing newly-born moose calves and fitting them with high tech collars that allow scientists to track the movements of the animals, assess habitat use, and determine if and when they die.
So far, of the 49 moose calves collared, just 18 remain on the air, although two of the calves slipped their collars so their fate is unknown. Of the roughly 30 calves known to have died, cows abandoned at least nine of them, apparently as a result of stress during the capture process, and a couple more died as a result of their capture.
Of the 38 calves that were not abandoned, at least six, and probably as many as nine, were killed by wolves. Three were killed by black bears and one drowned in a stream.
Lead DNR researcher Glenn DelGuidice says that’s roughly about what he anticipated. Other studies on whitetail deer suggested a 50 percent mortality rate for fawns in the first 12 weeks is fairly typical. “They are so vulnerable,” said DelGuidice. “Where you have viable populations of bears and wolves, they take a toll.”
While the mortality rate of newly-born moose calves is high, DelGuidice said it falls fairly rapidly as the young moose grow. “The risk of death drops continuously. In the last week, the mortality rate [for the moose calves] has dropped significantly,” he said.
Part of larger study
The moose calves are being collared and tracked as part of an ongoing DNR study that researchers hope will give them clues to the sudden and dramatic fall-off in the state’s moose population. Researchers collared more than 100 adult moose this past winter and are tracking those moose to learn more about how they use their forested landscape as well as to respond quickly when a moose dies. The quick response helps researchers better determine the cause of each moose death.
The DNR began tracking female moose most closely beginning in May as part of their plan to collar up to 50 calves in hopes of better understanding why calf survival has been so low in recent years. The DNR’s latest moose survey, conducted in January, found only 34 calves per 100 cows, a calf-to-cow ratio that was actually better than in some recent years, but well below the level necessary to maintain a healthy moose population.
The DNR researchers were able to track down 25 cows this spring, and collared a total of 49 of their offspring. They hope to repeat the process for at least the next two years, depending on funding.
Some good news
The calf study has yielded some encouraging news— most particularly the fact that a high percentage of moose cows gave birth to twins this year. So far, the research team has found 18 sets of twins, which is well above what they had expected. DelGuidice said the high percentage of twins probably reflects the fact that twins tend to be born earlier, so the first moose collared were more likely to be sets of twins. “Recently we’ve been seeing more singles,” said DelGuidice.
The high twin rate also usually means that the cows are in relatively good shape physically and nutritionally, so it’s a hopeful sign overall.
And while the calf mortality has been high, at nearly 50 percent so far, DelGuidice said the current calf-to-cow ratio is still up above 80 percent. “That’s not bad for this time of year,” he said. It is likely to be significantly less than that, however, when the DNR conducts its annual aerial moose survey this next winter. For calves that survive their first winter, the prospects of surviving to adulthood are good, said DelGuidice. “When they have survived a year, we refer to that as ‘recruitment,’” he added, since the young animal can now be considered a viable member of the population. “We might expect a 40 percent recruitment rate in a region with significant predation.”
While hard winters can be tough on moose calves, this year’s extended snowcover will likely yield some benefits down the road. “The late snowcover will probably reduce tick numbers,” said DelGuidice. Moose are particularly vulnerable to a species of tick known as a “winter tick,” which can attach by the tens of thousands. The ticks generally drop off moose in the late spring, and if there’s still significant snowcover and cold temperatures, most of the ticks don’t survive. A trend towards earlier spring snowmelt in recent years is one factor that many researchers believe could be negatively affecting moose in northeastern Minnesota. This year’s rather dramatic departure from that trend should help provide at least temporary relief from high winter tick numbers.
Whether it’s enough to turn around the region’s struggling moose herd remains to be seen.