Snowshoe hare populations across the boreal forest fluctuate on a cycle averaging about ten years, driven by a combination of predation and food supply. Because the Canada lynx takes hares as the overwhelming majority of its winter diet, its own reproduction and survival follow. Litter size falls, kitten survival collapses and adults disperse widely when hares crash.
The evidence base is unusually long. Hudson's Bay Company pelt returns from the eighteenth and nineteenth centuries preserve the oscillation across many decades, and the series became a textbook example in population ecology. Modern radio-telemetry and snow-tracking confirm the mechanism the fur records only implied.
The cycle is often presented as a clean predator-prey oscillation of the kind produced by simple mathematical models. Field experiments in the Yukon showed it is not that tidy: excluding predators and adding food each dampened the hare cycle, and only doing both together came close to flattening it. The lynx is one driver among several, not the sole cause.