The amplitude of the population fluctuations varies across the geographic range. It is greatest in the Northwestern Canada, and least in the rocky Mountain region of the United States, perhaps because there is more biological diversity in more southerly regions. The lack of diversity in the Northwestern portion of the hare's range means that there are fewer links in the food chain, and therefore fewer species to buffer either dramatic population increases or decreases. Disease may play a part in population fluctuation. Pneumonococcus, ringworm, and salmonella have all been associated with population crashes.
Snowshoe hares are also famous for their seasonal moults.
In the summer, the coat of the hare is reddish brown or grey, but during the winter, the coat is snowy white. The molt usually takes about 72 days to reach completion, and it seems to be regulated by daylength. Interestingly, there seem to be two entirely different sets of hair folicles, which give rise to white and brown hairs, respectively. References Baker, R.H. 1983. Mammals of Michigan.