The Lynx-Snowshoe Hare Cycle
The primary food of the lynx is the snowshoe hare and therefore the population cycles of these two species are closely linked. When hares are plentiful, lynx eat little else, taking about two hares every three days. When hares are scarce, lynx also prey upon mice, voles, squirrels, grouse, and ptarmigan, and they will also eat carrion. However, these food sources often do not meet the lynx's nutritional needs. Some lynx cannot maintain their body fat reserves, and become more vulnerable to starvation or predation. Other lynx manage to remain healthy by using alternative prey and food sources when the hares are low. When snowshoe hares are scarce, many lynx leave their home range in search of food.
Across most of the boreal forest, hare populations 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 hares per km2. The habitat cannot support this many animals, and as predation increases and starvation sets in, the population starts to decline. Continued predation accelerates the hare population decline, since lynx and other predators are at a population high. 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 1 to 2 years. As hare numbers start to decline, lynx continue to eat well because they easily catch the starving hares. When hares become scarce, the lynx numbers decline as well. 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 will breed and not all of those bred will produce litters. Litters will be smaller, and most, if not all, of the few kittens born will die soon after birth. This means that for a period of 3 to 5 years, few or no kittens survive to adulthood. Studies have shown that the level of kittens in a lynx population may be zero at the population low, and as high as 60% when their numbers are increasing. Low lynx population levels last for 3 or 4 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 1990's, lynx numbers peaked two years later in the north-western NWT than in the south-western NWT.