Moose are the largest members of the deer family, found throughout the northern forests of North America and Eurasia. The subspecies present in the upper Midwest, including Wisconsin, is the Western Moose (Alces alces andersoni). Wisconsin sits at the southern edge of this species’ natural range, meaning populations here are smaller and less stable than those further north. This marginal location explains why moose are present in the state, but their numbers remain exceptionally low.
Current Status and Distribution in Wisconsin
The current moose population in Wisconsin is small and generally not considered self-sustaining. Estimates from the Wisconsin Department of Natural Resources typically place the number of individuals between 15 and 40 animals. This small population is concentrated primarily in the far northern counties, especially those bordering Michigan’s Upper Peninsula, such as Iron, Vilas, Oneida, and Forest counties.
A significant portion of the state’s moose sightings are transient young bulls that have wandered south from established populations in Minnesota and Michigan. These migrating individuals seek new territory and mates, but the number of breeding-age females remains extremely low, often fewer than five. Consequently, the overall number of moose in Wisconsin fluctuates based on dispersal from neighboring states rather than sustained local reproduction.
Historical Context of Moose Presence
Moose were once more widespread across the northern half of Wisconsin, inhabiting the conifer-hardwood forests. They were present until the mid-to-late 1800s, though they were never as numerous as other members of the deer family. Unregulated hunting and widespread habitat destruction from logging and settlement led to their near-total elimination from the state.
By the early 1900s, moose were considered extirpated from Wisconsin’s borders. Their return began slowly in the 1960s, driven by the natural expansion of growing moose populations in neighboring Minnesota. This recolonization was not the result of a state-run reintroduction program. The first documented birth of a wild moose calf in Wisconsin in over a century occurred in 2002, marking a small milestone in the species’ slow return.
Ecological Factors Limiting Population Growth
The primary reason moose remain so rare in Wisconsin is a combination of biological and environmental pressures that limit their survival and reproduction.
Climate Change and Heat Stress
Moose are a cold-adapted species, and the warming climate at the southern edge of their range presents a significant physiological challenge. Warmer summer temperatures force moose to reduce their daytime feeding activity, often seeking refuge in dense cover or water to cool down.
This behavioral change, particularly when temperatures exceed their thermal tolerance thresholds of around 60 to 70 degrees Fahrenheit, results in reduced food intake and subsequent malnutrition. Entering the winter season in poor condition lowers their resistance to disease and negatively impacts reproductive success the following spring. This chronic heat stress creates a cumulative physiological toll that acts as a major barrier to population growth.
Brainworm Parasite
Another limiting factor is the presence of a parasitic nematode known as Parelaphostrongylus tenuis, or brainworm. This parasite is carried harmlessly by white-tailed deer, but it is lethal to moose, causing neurological damage that often leads to paralysis and death. The parasite’s life cycle involves terrestrial gastropods—snails and slugs—which moose can accidentally ingest while browsing on vegetation.
Wisconsin has a high density of white-tailed deer throughout the northern region, elevating the transmission risk of brainworm to moose. Deer densities in much of northern Wisconsin exceed the threshold of 10 deer per square mile, which threatens moose survival. The abundant deer population acts as a reservoir for the parasite, creating a continuous infection threat that prevents the establishment of a stable, self-sustaining moose population.