The question of which bear species reigns supreme in size often comes down to a comparison between two formidable North American apex predators: the Polar Bear (Ursus maritimus) and the Grizzly Bear (Ursus arctos horribilis). Both species are incredibly powerful mammals that dominate their respective ecosystems. Determining which one is the true giant requires a close look at their physical characteristics. While both are massive, their distinct evolutionary paths have resulted in noticeable differences in their average weight and overall stature.
The Arctic Giant Polar Bear
The Polar Bear is widely recognized as the largest extant bear species and the world’s biggest land carnivore. Adult male Polar Bears, known as boars, typically weigh between 770 and 1,500 pounds, though some exceptionally large individuals have been recorded at over 1,700 pounds. They possess a long, narrow skull and a relatively slender body, an adaptation that aids in swimming and hunting seals. The average male measures between 8 and 10 feet from the tip of the nose to the tail. When standing on all four paws, boars can reach a shoulder height of up to 5.2 feet. Female Polar Bears, or sows, are significantly smaller, generally weighing between 330 and 660 pounds. This species is highly specialized for life on the Arctic sea ice, where its nearly exclusive diet of marine mammals, particularly ringed seals, provides the high-calorie fat reserves necessary for survival.
The North American Grizzly Bear
The Grizzly Bear, a subspecies of the brown bear, is a powerful mammal found across the mountainous and forested interior regions of North America. Inland male Grizzly Bears generally weigh between 400 and 790 pounds, showcasing a considerable range dependent on local food availability. These bears are distinguishable by the prominent muscular hump on their shoulders, which provides great strength for digging and tearing. An average adult male Grizzly can reach a length of 5.5 to 8 feet and can stand up to 8 feet tall on its hind legs. Females are noticeably smaller, with their average weight falling between 250 and 350 pounds. Unlike the highly carnivorous Polar Bear, the Grizzly is an omnivore, relying on a varied diet that includes plants, berries, roots, and occasional fish or small mammals.
Head to Head Size Comparison
When comparing the two species, the Polar Bear is definitively the larger animal on average. A typical male Polar Bear weighs hundreds of pounds more than a typical male Grizzly Bear. The average male Polar Bear sits comfortably in the 1,000-pound range, while the average inland Grizzly Bear is closer to 600 pounds. This size disparity is most evident when considering the maximum recorded sizes. The largest verifiable Polar Bears have exceeded 2,200 pounds, a weight that significantly surpasses the heaviest recorded mainland Grizzly Bears. Polar Bears are also generally longer, with males regularly reaching 10 feet in total length, compared to the Grizzly’s maximum of about 8 feet. The Polar Bear’s massive body size makes it appear bulkier and longer.
Why Polar Bears Evolved to Be Larger
The Polar Bear’s superior size is a direct result of evolutionary pressure from its frigid Arctic environment and its specialized diet. Its enormous body mass provides a significant advantage for thermoregulation, aligning with Bergmann’s Rule, which suggests that larger animals are found in colder climates. A greater body volume-to-surface area ratio allows the animal to retain heat more effectively in sub-zero temperatures. The bear’s immense size is sustained by a diet almost entirely composed of high-fat marine mammals, primarily seals. Seal blubber is incredibly calorie-dense, providing the energy intake required to fuel and maintain such a large frame. In contrast, the Grizzly Bear’s omnivorous diet, which often includes lower-calorie vegetation and berries, does not support the same level of growth.