Lemming, the small, thickset rodent of the circumpolar north, is an iconic mammal of the Arctic tundra. This creature’s fame stems almost entirely from sensationalized accounts of its mass movements across the barren landscape. Understanding the lemming’s behavior requires looking beyond folklore to the complex ecological forces that drive its life. These dramatic periods of movement are directly linked to the species’ unique population dynamics in a volatile polar environment.
Understanding Lemming Population Cycles
Lemming populations follow a predictable, explosive biological pattern known as a boom-and-bust cycle. They typically follow a 3- to 5-year cycle, with peaks occurring roughly every 3.7 years in many regions. Population growth is fueled by abundant food, low predation pressure, and favorable weather. This includes a deep, stable snowpack that allows them to reproduce safely throughout the winter months.
During the “boom” phase, reproductive success is so high that populations can increase dramatically, sometimes by a factor of ten in a single year. The subsequent “bust,” or crash, is a natural consequence of this overabundance, not the movement itself. High density causes lemmings to rapidly deplete local food resources, such as grasses and sedges, leading to overgrazing and starvation.
Overcrowding also leads to increased aggression and susceptibility to disease, further contributing to the population collapse. Studies suggest that the decline phase, characterized by high mortality, often occurs during the summer when the animals are exposed to predators.
Dispelling the Myth of Mass Suicide
The public misconception that lemmings intentionally march off cliffs to commit mass suicide is entirely false. This enduring myth was cemented in popular culture by the 1958 Walt Disney nature film, White Wilderness. The documentary featured a sensationalized scene showing the rodents plunging into the ocean.
The lemming scene was later revealed to be completely staged by the filmmakers. The crew acquired lemmings from a distant location and transported them to Alberta, Canada, outside their natural habitat range. For dramatic effect, the lemmings were forced off a cliff and into a river, using careful editing to create the appearance of a deliberate, mass act.
The Reality of Lemming Dispersal
The large-scale movement observed on the tundra is not a coordinated migration, but rather a chaotic dispersal driven by desperation. When local population density reaches unsustainable levels and food supplies are exhausted, individual lemmings or small groups begin moving erratically in all directions to search for new, less-crowded feeding grounds. This movement is a scramble for survival, triggered by an immediate need for resources.
As lemmings move across the landscape, they encounter natural obstacles, including rivers, lakes, and fjords. Lemmings are capable swimmers and will attempt to cross these bodies of water, often mistaking them for smaller barriers. Drowning deaths occur accidentally when the water body is too wide or turbulent, exhausting the animals before they can reach the other side.
The apparent mass movement is simply the cumulative effect of thousands of individuals simultaneously dispersing from a center of overpopulation. Any perceived directionality is often an illusion caused by geographic features, such as a valley or shoreline, that funnel the dispersing animals into a narrower path.
Ecological Impact on the Tundra
The lemming population cycle establishes the animal as a keystone species in the Arctic ecosystem. Their oscillating numbers create a feast-or-famine scenario for tundra predators, including the Arctic fox, snowy owl, and stoat. When lemmings are abundant, these predators experience reproductive success, raising large litters or clutches due to the surplus of easily available food.
During the “boom” years, lemmings also significantly impact vegetation through intense grazing. They consume grasses, mosses, and sedges, temporarily altering the plant community and affecting soil nutrient dynamics. When the lemming population crashes, the sudden scarcity of their primary prey causes a corresponding collapse in predator populations.
Specialized predators, particularly the snowy owl, may fail to reproduce entirely or must migrate south in search of other prey. Generalist predators like the Arctic fox may switch to eating birds and their eggs. This shift in predation pressure on other species, such as waders and ptarmigans, demonstrates the cascading effect of the lemming cycle throughout the food web. The return of the lemming population years later is what allows the predator populations to recover.