The parasite rarely affects deer but commonly develops into a meningeal brain worm that can kill moose. In the 1950s and '60s, it was common to see moose in a dazed condition, walking in circles, and eventually dying from the effects of brain-worm infestation. But when modern clear-cutting practices came to the north woods, moose populations began to rise and spread south once more into ranges that had been usurped by deer. As moose continued to increase and overlap with deer range, the brain-worm problem began to subside. It is possible that moose are developing resistance to the parasite, but biologists think that, more likely, deer and moose are merely choosing separate feeding areas even though they share occupancy of the same general ranges.
Deer feed around the edges of clear-cuts more than out in the middle.
In winter, deer avoid exposure to cold wind and stay in protected places, while large-bodied moose just turn their rumps to the wind and continue to feed in the open. Furthermore, deer numbers are declining in the heavily clear-cut areas for lack of sufficient cover. Although permits entitle them to take animals of either sex, most moose hunters select antlered bulls. This tendency does not slow the population growth. Before moose in certain densely populated regions reach numbers that cause unacceptably high vehicle-collision rates or other unwelcome costs, moose managers can reduce and stabilize the population at a justifiable level simply by issuing permits allowing a certain number of hunters to take females only.