The Kodiak bear (Ursus arctos middendorffi) is a subspecies of the brown bear and one of the largest terrestrial carnivores on Earth. This massive animal is found exclusively within the Kodiak Archipelago, a group of islands off the southern coast of Alaska. The unique geography and rich ecosystem of this isolated habitat allowed the Kodiak bear to evolve into a giant.
Benchmark Weights and Dimensions
The weight of a mature Kodiak bear varies significantly between the sexes and across the seasons. Adult males (boars) generally range from 600 to 1,400 pounds (272 to 635 kilograms), averaging between 1,050 and 1,177 pounds annually. Females (sows) are substantially smaller, weighing between 300 and 700 pounds (136 to 318 kilograms). The heaviest wild Kodiak bear reliably recorded weighed 1,656 pounds (751 kilograms).
A large male stands approximately 4 to 5 feet tall at the shoulder when walking on all four legs. When a boar stands upright on its hind legs, it can reach up to 10 feet in height. This combination of immense mass and height illustrates why the Kodiak bear is cited as one of the two largest bear types in the world.
Seasonal Weight Fluctuation
Kodiak bear weight is not static but represents a cycle of seasonal change driven by the need to prepare for winter hibernation. During hyperphagia in late summer and fall, bears gorge on food to build fat reserves, increasing their body mass by 20 to 40%. This rapid weight gain is necessary for survival, as the stored fat sustains them through their winter sleep.
Females also rely on fat accumulation for reproduction; the fertilized embryo will only implant in the uterine wall (delayed implantation) once the sow has adequate body fat. Since they do not eat, drink, or excrete during their denning period, Kodiak bears emerge in the spring at their lowest weight, having lost between 20% and 40% of their body mass. This annual cycle of feasting and fasting is a necessary mechanism for survival in the Alaskan environment.
Comparison to Other Large Bears
The Kodiak bear competes for the title of the world’s largest bear, primarily against the Polar bear and the Continental Grizzly. As a coastal brown bear, the Kodiak subspecies can weigh approximately twice as much as the inland-dwelling Continental Grizzly bear (Ursus arctos horribilis). The average Continental Grizzly male weighs considerably less, usually between 400 and 790 pounds.
The comparison with the Polar bear (Ursus maritimus) is nuanced and depends on whether one considers average or maximum size. Polar bears are recognized as the largest bear species, with males averaging between 1,000 and 1,200 pounds, comparable to the Kodiak’s average. However, the Polar bear holds the record for the largest specimen ever recorded, which was over 2,200 pounds, exceeding the Kodiak’s documented maximum.
Factors Influencing Their Massive Size
The Kodiak bear’s massive proportions result from a convergence of environmental and genetic factors. Their size is a textbook example of island gigantism, a phenomenon where the absence of mainland predators and competitors allows a species to evolve larger body sizes. Kodiak bears have been genetically isolated on the archipelago for approximately 12,000 years, allowing this evolutionary path to solidify.
The primary driver of their bulk is the year-round availability of a rich, high-protein diet. The archipelago supports runs of five species of Pacific salmon, providing the bears with an enormous caloric windfall during the summer. This is supplemented by nutrient-dense vegetation, including grasses, roots, and high-sugar elderberries, which allows them to accumulate the fat stores necessary for their size.