Studies on a Population Cycle of Snowshoe Hares on the Lake Alexander Area I. Gross Annual Censuses, 1932-1939

gaged man's attention for centuries. The well-known tale of the Pied Piper has been said to be a mythical outgrowth of the lemming years that occur periodically in Norway. The archives of the Hudson's Bay Company have yielded substantial evidence of fluctuation in mammalian populations in North America extending back more than a century. This phenomenon has been studied chiefly in the Northern Hemisphere, but it has been observed also in voles in the Southern Hemisphere (Hudson, 1918). The species of animals subject to these periodically recurring changes in abundance are remarkably varied. Snowshoe hares, field mice, ruffed grouse, lynxes, wolves, and even some kinds of fishes are recognized as being cyclic The basic problem of population cycles is to be found among the resident plant-eating species. The snowshoe hare, the meadow mouse, and the ruffed grouse, which subsist largely on plant life, experience extreme changes from abundance to scarcity at regularly recurring intervals, in spite of an apparently more than adequate food supply. Evidence has been presented which indicates that changes in the population of predators lag a year or two behind fluctuations in the abundance of the animals that constitute their usual prey. That is, the cycles observed in carnivores are considered a secondary result of the changes in the population of herbivorous species. In our attack on the general problem of fluctuations in population, we have worked principally with the snowshoe hare (Lepus americanus). This species, which goes through violent periodic fluctuations in abundance, was found to be suitable for the application of procedures necessary for adequate censusing and disease investigation.