Vermont’s Moose Herd

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Changing Winds for the Iconic Moose

Climate change in the northern woods is making life increasingly difficult for many wildlife species. Moose are particularly under stress. Fluctuations in temperatures, shifts in the timing of seasons, and alterations in habitat quality are only some factors affecting moose. In addition, two worrisome parasites are taking advantage of the changing climate to target moose with deadly results: brainworm and winter ticks.

A parasite commonly found in the brain and skull of white-tailed deer, brainworm does not have a negative impact on deer and their family members. But moose, who are a more recent host, are severely affected, with brainworm proving fatal to the infected animal. As winters become milder and less snowy, deer populations rise, making their encounters with and infection of moose more common. To protect moose from brainworm, reducing deer populations where they overlap with moose is possibly the only solution.

Winter ticks, however, offer fewer options. The second parasite impacting moose, winter ticks are native to the northern forest. Due to longer fall and earlier spring seasons, tick populations have increased opportunities to find hosts and reproduce. Unlike black-legged ticks, which are associated with deer and Lyme disease, winter ticks aren’t known to pass diseases to humans or domestic animals. Unfortunately, though, they can severely impact moose. Ten of thousands of winter ticks can attach to a single moose, draining its blood and causing the moose to become weak and irritated. Infected moose often rub against trees, scraping their insulative hair off in the process, and becoming susceptible to hypothermia. Moose calves are the most severely affected by tick infestations. Individual calves can get more than 20,000 ticks on them during the winter and many die from anemia. Ultimately, winter ticks have the potential to kill 30 to 70 percent of moose calves per winter.

To better assess Vermont’s moose herd and the effect of winter ticks, the Vermont Fish & Wildlife Department is conducting a 3-year study. Thirty calves are captured each year, along with enough cows (adult females) to maintain a total study population of 30 adults. Each is fitted with a GPS collar. Biologists hope to learn whether predators, parasites, or other stressors cause moose mortality. They are also examining reproductive success and where the calves go after they leave their mother’s side. By 2020 biologists hope to devise a long-term strategy to reduce the impacts of winter ticks. This may mean maintaining a lower moose population, as higher moose densities may increase moose’s susceptibility to ticks. Hunting may play an important role in reducing the number of moose that die every year from winter ticks.

In Vermont, initial efforts to reduce moose numbers into balance with the available habitat may have also reduced tick infestations. But time will tell.

To counter these effects, landowners can help moose by providing good habitat, such as wetlands and young forest, that will help maintain populations into the changing future. That way we can ensure these magnificent animals walk among the forests and fields of Vermont for generations to come. Landowners who are interested in improving habitat for moose can contact biologist Andrea Shortsleeve at andrea.shortsleeve@vermont.gov.