The crust on the snow during the night makes all moose quite vulnerable to predators. Cows often calve on the south side of hills for this reason. The wolves travel on top of the snow, and the moose's' legs are cut by the crust, greatly impeding their escape and defense. Before breakup they are still in the hills avoiding the river where there is clear ice and potential flooding. After breakup, cows and calves are often on the river for the protection the water provides.
Bears kill more moose calves than wolves, although both are devastating.
Summer Mosquitoes and horse flies often drive them to the water, either the lakes or rivers where they remain up to their bellies protecting the areas of their bodies that have thin hair. If they aren't in the water, they seek windy places that keep the mosquito hoard down. Moose, particularly cows with calves stay close to the water because the first line of defense for a moose is to go to the water where their long legs keep them on the bottom while predators are swimming. The moose can beat a bear or wolf in the water. The moose are either in the hills or on the lakes.