The lemming, a small Arctic rodent, is a consequential prey species in the northern hemisphere. Species like the Norway lemming and the brown lemming inhabit the vast, cold expanse of the tundra, remaining active year-round beneath the snowpack. These stout herbivores primarily feed on sedges, mosses, and grasses, serving as a biological engine for the Arctic food web. Their abundance and predictability make them a keystone species, directly influencing the survival and reproductive success of many tundra predators.
Key Avian and Mammalian Hunters
Predators of lemmings fall into two categories: highly specialized hunters that rely on them for breeding success and opportunistic generalists. Among avian hunters, the Snowy Owl (Bubo scandiacus) is the most closely linked to lemming populations. These large, nomadic owls depend entirely on high lemming density for successful breeding, often requiring two or more per hectare to attempt nesting. They hunt by sight during the Arctic summer, catching lemmings with swift dives.
Other significant avian predators include the Long-tailed Skua (Stercorarius longicaudus) and the Rough-legged Hawk (Buteo lagopus), migratory visitors that time their arrival with the summer lemming peak. The Long-tailed Skua shifts its diet from alternative food sources, such as insects and berries, to lemmings once rodent density reaches a certain threshold. Mammalian predators include the Arctic Fox (Vulpes lagopus), the most prominent resident hunter. The Arctic Fox is a highly adapted specialist that caches lemmings during peak years to sustain itself and its young through leaner times.
The smaller, highly specialized stoats and weasels (Mustela species) are formidable predators capable of following lemmings directly into their underground burrows. The stoat is considered one of the most specialized predators, possessing a delayed numerical response that allows its population to peak after the lemming population has begun to crash. Larger carnivores like wolves and occasionally Grizzly Bears will opportunistically consume lemmings when encountered, but these rodents do not form the main component of their diet. The collective pressure from this diverse guild of predators represents the largest cause of lemming mortality.
The Critical Role of Population Cycles
The relationship between lemmings and their predators is defined by the notorious 3-to-4-year boom-and-bust population cycle. During the “boom” phase, lemming numbers can explode, reaching densities of hundreds of individuals per hectare. This cycle is driven by high reproductive rates and favorable weather, while the subsequent crash is induced by resource depletion, social stress, and increased predation.
This predictable fluctuation dictates the reproductive success of the entire Arctic predator community. Predators exhibit two primary reactions: a “functional response” and a “numerical response.” A functional response describes how an individual predator consumes more lemmings per day when they are abundant. The numerical response is the increase in the predator population itself, usually through larger litter sizes or higher breeding attendance during peak lemming years.
The most specialized predators, like the Snowy Owl, display a step-like numerical response, only breeding when lemming densities are high enough to support their nestlings. This tight coupling means a successful year for lemmings translates directly into a successful breeding year for the Snowy Owl, Arctic Fox, and Long-tailed Skua. The stoat’s numerical response is delayed by a year; its population peak arrives just as lemming numbers are falling, which is a significant factor in driving the lemming population into its low phase.
Survival Tactics and Anti-Predator Behavior
Lemmings have developed behavioral and physical adaptations to navigate constant predation pressure. Their primary defense is the creation of complex, multi-chambered burrow systems, which provide shelter from Arctic weather and surface predators. During winter, lemmings live and breed in the subnivean zone—a layer of insulated space between the snow and the ground—where their tunnels are largely inaccessible to aerial hunters.
Camouflage is another effective tactic, as most lemming species possess fur coloration that blends seamlessly with the brown and gray tones of the tundra. The Norway lemming is a notable exception, displaying a bold, contrasting coat of black, yellow, and white. When cornered, this species switches from concealment to an aggressive warning display, emitting loud squeaks and charging at a perceived threat while exposing its sharp incisor teeth. This aggressive behavior is a rare form of anti-predator defense in small rodents, signaling that the lemming may not be an easy meal.
When Lemming Numbers Crash
The ecological consequences of a lemming population crash are immediate and widespread, creating a ripple effect across the Arctic ecosystem. As lemming numbers plummet, specialized predators face a severe food shortage, leading to widespread starvation and failed breeding seasons. Snowy Owls, which cannot raise young without a steady supply of lemmings, often forgo breeding entirely or migrate hundreds of kilometers south in search of alternative prey.
This low point in the lemming cycle forces generalist predators, such as the Arctic Fox, to switch their focus to alternative food sources, a phenomenon known as the “alternative prey hypothesis.” This shift results in increased predation pressure on the eggs and nestlings of Arctic-nesting birds, such as geese and shorebirds, whose reproductive success consequently declines. The crash also marks the end of the famous mass movements, often misinterpreted as a coordinated “suicide” event. These migrations occur during population peaks when the animals are searching for new, less crowded habitats, and deaths from accidental drowning in water crossings are a consequence of desperate movement, not intentional self-destruction.