Reindeer, known as caribou in North America, are large ungulates that inhabit the vast tundra and boreal forests of the Arctic and subarctic regions. These animals are famous for their immense seasonal migrations, with some herds traveling thousands of miles between their summer and winter ranges. This nomadic lifestyle exposes them to a continuous threat from predators, establishing an ecological relationship that shapes the survival and movement of the herds. The threat from these carnivores is a selective pressure, forcing reindeer to maintain highly developed physical and behavioral adaptations.
Apex Predators The Wolf
The Gray Wolf (Canis lupus) stands as the most significant natural predator of reindeer and caribou throughout their circumpolar distribution. Wolves are highly effective pack hunters, relying on intelligence, communication, and exceptional endurance to pursue large prey. They can maintain a steady lope of 5 to 6 miles per hour for hours, eventually closing the distance on prey.
When hunting reindeer, the pack’s strategy involves testing the herd to identify vulnerable individuals, such as the old, sick, or young. This often involves a pursuit that can reach sprinting speeds of 35 to 40 miles per hour, though their success rate is generally low (10 to 25 percent). Wolves also use terrain and environmental conditions, like deep snow, to their advantage, as this slows the reindeer’s escape.
Other Large Mammalian Threats
Beyond the wolf, other large mammalian carnivores, particularly bears, exert considerable pressure on reindeer populations. Brown Bears (Ursus arctos), including the North American Grizzly, are especially formidable during the spring calving season. These bears are not pursuit predators like wolves but instead employ an active hunting strategy focused on ambush and targeting vulnerable newborns.
A single brown bear can kill dozens of newborn calves during the few weeks of the calving period. Polar Bears (Ursus maritimus) also prey on reindeer, especially in coastal areas like the Svalbard archipelago, where diminishing sea ice has forced them to spend more time on land. These bears may chase reindeer into the water, where the bear’s strength and swimming ability give it a distinct advantage, or utilize surprise to overcome adult reindeer.
Opportunistic Predators of Young Reindeer
Smaller, yet still formidable, predators focus their energy on the most vulnerable segment of the population: the calves, which are born synchronously in late spring. The Wolverine (Gulo gulo) is a tenacious predator known for its ability to kill young reindeer, often contributing to a significant portion of calf mortality in some regions. Wolverines are powerful for their size and will opportunistically attack calves separated from the main herd.
Large avian predators, such as the Golden Eagle, are also a threat to very young calves. These eagles primarily target newborns that are lighter in weight, snatching them from the ground. This type of predation is highly seasonal, occurring immediately after birth, and is often a localized factor.
Reindeer Defense Mechanisms
Reindeer have developed several sophisticated defense strategies to mitigate the constant threat from multiple predators. The most visible defense is the mass migration and formation of immense herds, which can number in the hundreds of thousands of individuals. This sheer number acts as a dilution effect, reducing the statistical chance of any one animal being targeted during an attack.
When directly threatened, the herd may engage in a defensive maneuver known as a “reindeer cyclone,” where they run in a tight, swirling circle. This chaotic movement makes it difficult for a predator to focus on a single target, while the strongest adults form a protective outer perimeter, shielding the calves and weaker individuals in the center. Reindeer also possess impressive physical capabilities, including the ability to run up to 50 miles per hour and use their sharp hooves to strike at attackers.