The lemming, a small rodent of the Arctic Tundra, is a foundational species. These herbivores, including species like the Siberian and collared lemmings, inhabit the treeless Arctic and alpine environments across the Northern Hemisphere. They forage on grasses, mosses, and sedges, often under the protective layer of snow during winter. Despite their diminutive size, lemmings represent a massive, concentrated energy source for specialized predators. Their abundance is the primary driver for the reproductive success and population dynamics of many other animals in the harsh tundra ecosystem.
Avian Predators of the Tundra
Avian hunters are direct beneficiaries of lemming abundance, with many species demonstrating a reproductive strategy tightly bound to prey availability. The Snowy Owl is a major and specialized predator, with its breeding success almost entirely dependent on high lemming densities. In peak lemming years, Snowy Owls will nest in large numbers and lay clutches of up to 12 eggs, stockpiling dead lemmings around the nest to feed their young. In contrast, when lemmings are scarce, these owls often forego breeding entirely in a given area.
Other birds of prey, such as the Rough-legged Hawk (or buzzard), also exhibit a strong response to lemming availability. These migratory raptors arrive at their breeding grounds in mid-spring and only commence laying eggs if the local lemming population is sufficiently high. If the food supply is poor, many Rough-legged Hawks abandon the breeding areas early in the season. For these raptors, lemmings can constitute between 6% and 95% of their diet during the breeding season, illustrating their reliance on the rodent.
The Arctic Skuas, specifically the Long-tailed and Pomarine Skuas (or Jaegers), are also significant lemming predators. These seabirds shift their diet on the breeding grounds to focus heavily on lemmings. Like the owls and hawks, their nesting density and reproductive output increase sharply with rising lemming numbers, synchronizing the life cycles of these nomadic avian specialists.
Mammalian Hunters of the Tundra
The tundra’s mammalian carnivores also rely heavily on lemmings, with the Arctic Fox being the most prominent example of a resident specialist. For the Arctic Fox, lemmings form the main component of their summer diet, and their reproductive success is closely tied to the rodent’s population peaks. During “lemming years,” a female Arctic Fox may give birth to large litters, sometimes as many as 18 cubs.
Mustelids, such as the stoat or ermine, are effective predators due to their small size and ability to hunt beneath the snow. The ermine, which is completely at home in the subnivean layer, can access lemming nests and prey on the rodents even during the winter months. This specialized hunting ability makes the ermine a consistent source of predation pressure during the critical winter period for lemming population dynamics.
Larger, more generalist predators also take lemmings opportunistically, though the rodents are a minor part of their overall diet. Wolves and wolverines consume lemmings when they are abundant and easily accessible. Even Polar Bears, primarily marine hunters, have been known to take lemmings, demonstrating the prey’s widespread appeal when densities are high. For these larger carnivores, lemmings provide a temporary, localized food source that supplements their usual diet.
The Impact of Lemming Population Cycles
Lemming populations follow “boom-and-bust” cycles, which typically occur every three to five years. During a boom, the lemming density can increase dramatically, sometimes from a low of a few individuals per hectare to over 100 per hectare. This resource pulse creates a wave of abundance that cascades through the entire tundra food web.
The reproductive output of specialized predators is directly linked to these cycles. During a lemming peak, predators like the Snowy Owl and Arctic Fox experience explosive breeding success, producing large litters and high numbers of fledglings. However, the predator population peak often occurs with a slight delay, about a year after the prey peak.
This delayed response means that when the predators reach their highest numbers, the lemming population is already beginning its crash. The intense predation pressure, combined with other factors, drives the lemming numbers down to the low phase of the cycle. The subsequent famine causes the reproductive success of the specialized predators to crash, as they cannot sustain their young without the primary food source. The populations of the predators rise and fall in a predictable, synchronized pattern with their primary prey.