Northern Wilds

At the recent Minnesota Large Mammal Conference in Grand Rapids, biologists presented bad news and good news about the state’s moose population. The bad news is that the northwestern herd has diminished nearly to nonexistence and the northeast herd also appears to be in long term decline. The good news is that state and tribal biologists are taking whatever steps they can to learn more about Minnesota and make on-the-ground habitat improvements.

The problems faced by Minnesota moose have been widely reported, but from a scientific perspective, are not well understood. The northwest herd went into precipitous decline in the 1990s. Eric Cox, the graduate student who was trying to learn why the decline occurred, was tragically killed in an airplane accident along with a DNR pilot during an aerial survey. The northeast decline is more recent. State and tribal wildlife authorities are collaborating in an ongoing radio-collar study to learn more about northeast moose mortality.

Scientists suspect an underlying factor in the declines is a warming climate, because Minnesota is on the southern fringe of of the moose range and the weather has warmed significantly in recent decades. Dr. Warren Ballard, who presented some findings from Eric Cox’s research, said that mean monthly temperatures, dates of the first and last freeze, and length of growing season have all trended toward warming. This in turn may have affected aspects of moose survival.

Very simply put, Ballard explained a warming climate favors deer and brings other factors into play, including more parasites, marginal habitat, trace element deficiencies (such as copper), poor nutrition, and high mortality rates. He predicts the northwest moose population will be extinct within 50 years and that the southern edge of the continental moose range will move northward.

In the northeast, radio-collar research is ongoing in central Lake County and scientists plan to collar another 30 moose this winter using funding from a federal tribal wildlife grant, which was obtained with assistance from Senator Coleman’s office. Currently, 31 collared moose are roaming the forest, while 81 have died during the course of the study. The moose mortality ranges from natural causes such as moose predation, to human-related factors such as vehicle collisions. However, 29 moose have died for reasons unexplained. They are the ones that perplex the scientists.

Through the study, researchers have learned northeast moose carry high numbers of winter ticks. Many of the dead moose they examine are malnourished, even though food is abundant. They also suspect that parasitic brainworms are infecting some moose, though this is difficult to detect. All of the above is leading to unusually high mortality rates—up to 34 percent annually. But again, as in the northwest, there is no single factor biologists can point to as the cause of high mortality.

At present, biologists say moose in the northeast are not endangered—the population is estimated at 6,500 animals—and the annual state and tribal hunts will continue. The state has restricted the harvest to bulls only, which wildlife managers say won’t affect the overall population. There are presently 80 bulls per 100 cows in the northeast herd.

At the field level, wildlife managers are taking steps to identify the best moose habitat in the northeast and manage it to benefit the animals. Tom Rusch, wildlife manager in Tower, said DNR wildlife managers are working with foresters to plan timber harvests that mimic natural disturbances such as fire and blowdown. Large, natural openings within a mosaic of forest cover are considered good for moose.

"It all comes down to sunlight hitting the ground," Rusch said.

In addition to openings, moose need conifers for thermal cover in winter and summer. In some areas with low productivity for timber, shearing brush can restore browse. In some instances, DNR Wildlife is contributing money to the U.S. Forest Service for prescribed burns to reduce fuel loads. Overall, Rusch says, cooperation with the Forest Service is vital to the success of moose management, because much of the northeast moose range is within the Superior National Forest.

One aspect of moose management is beyond the reach of wildlife biologists and foresters: snow cover. The northeast moose range correlates closely with the portion of the state that has 12 inches of snow cover for at least 65 days per year. In the core of the northeast range, a foot of snow covers the ground for an average of 90 days each year. Unfortunately, average snows haven’t fallen in recent years.

"We need to return to winters with 40 inches of snow on the level and we haven’t seen that since 1997," Rusch said.

While biologists lack answers, they do have data. Minnesota DNR biologist Mark Lenarz said that heat stress in summer and winter may be affecting moose, which need cold weather. He pointed out that the upper critical temperature for moose is the lower critical temperature for deer. This means as the climate grows to warm for moose, it becomes warm enough for deer.

Lenarz said little is known about heat stress on deer and moose, but more is known about domestic cattle. When it is too hot for cattle, their food intake is decreased, weight and milk production are reduced, and the immune system may be impaired. Similar things may be happening with moose.