Snowshoe hare is the primary food of the lynx. The population cycles of these two species are closely linked.
When hares are plentiful, lynx eat little else and take about two hares every three days.
Lynx prey upon mice, voles, squirrels, grouse, ptarmigan and carrion when hares are scarce. These food sources often do not meet the lynx's nutritional needs. Some lynx cannot maintain their body fat reserves on this type of diet and become more vulnerable to starvation or predation. Other lynx manage to remain healthy by using alternative prey and food sources when the hare population is low. When snowshoe hares are scarce, many lynx leave their home range in search of food.
Hare populations across most of the boreal forest experience dramatic fluctuations in a cycle that lasts 8-11 years. At the peak of the cycle, snowshoe hares can reach a density of up to 1500 animals per km2. The habitat cannot support this many animals. As predation increases and starvation sets in, the population starts to decline. Continued predation due to high populations of lynx and other predators increases the hare population decline.
When the hare population reaches a low level, it stabilizes, for several years. The food plants slowly recover and the hare population starts to increase again. Since hares have several litters each year, the hare population increases rapidly. After a year or two at high densities, the hare cycle repeats itself.
The lynx population decline follows the snowshoe hare population crash after a lag of one to two years. As hare numbers start to decline, lynx continue to eat well because they can easily catch the starving hares.
When hares become scarce, lynx numbers also decline. Their lack of fat reserves makes them less able to live through starvation and cold temperatures. Food shortages also cause behavioural changes such as increased roaming and loss of caution. This increases their vulnerability to predation.
Malnourishment has the most significant effect upon lynx reproduction and population levels. When females are in poor condition, fewer breed and not all of those bred produce litters. Litters are smaller, and most, if not all, of the few kittens born die soon after birth. This means that for a period of three to five years, few or no kittens survive to adulthood. Studies have shown the level of kittens in a lynx population may be zero at the population low and as high as 60 percent when t numbers increase. Low lynx population levels last for three or four years. When hares become plentiful again, the lynx population begins to increase as well.
The highs and lows of the lynx population cycle do not occur at the same time across the NWT. For example, in the early 1990s, lynx numbers peaked two years later in northwestern NWT than in the southwestern NWT.