Bears vary greatly in weight, not only between species but also among individuals. This article explores the typical weight ranges for various species and the biological and environmental factors influencing a bear’s mass.
Weight Variation Among Bear Species
Bear species show a wide range in size and weight. Polar bears (Ursus maritimus) are the largest bear species and the largest land carnivores, with adult males weighing 300 to 800 kilograms (660–1,760 pounds) and females ranging from 150 to 300 kilograms (330–660 pounds). Brown bears (Ursus arctos), including grizzly and Kodiak bears, also grow large. Male grizzly bears weigh 180 to 360 kilograms (400–790 pounds), while females are 130 to 180 kilograms (290–400 pounds). Coastal brown bears and Kodiak bears, with abundant food, can exceed these weights, with males often reaching over 450 kilograms (1,000 pounds).
American black bears (Ursus americanus) are smaller, with adult males weighing 57 to 250 kilograms (126–551 pounds) and females 41 to 170 kilograms (90–375 pounds). Asian black bears (Ursus thibetanus) are comparable, with males weighing 60 to 200 kilograms (130–440 pounds) and females 40 to 125 kilograms (88–276 pounds). Giant pandas (Ailuropoda melanoleuca) fall within the range of 86 to 125 kilograms (190–275 pounds) for males and 70 to 100 kilograms (155–220 pounds) for females.
Sloth bears (Melursus ursinus) and sun bears (Helarctos malayanus) are at the smaller end of the spectrum. Sloth bear males weigh 80 to 145 kilograms (176–320 pounds), and females weigh 55 to 105 kilograms (121–231 pounds). The sun bear is the smallest bear species, with males weighing 40 to 70 kilograms (88–155 pounds) and females 25 to 50 kilograms (55–110 pounds).
Key Factors Influencing Bear Weight
Several factors contribute to weight variations within a bear species and in individual bears over time. Sex is a primary determinant, as male bears are larger and heavier than females across most species. This sexual dimorphism is pronounced in larger species like polar bears, where males can be more than twice the weight of females.
Age also plays a substantial role in a bear’s weight. Bears increase in mass as they mature, reaching peak weight in adulthood. Their weight may then decline in old age. Seasonal changes dramatically impact bear weight, especially in species that hibernate. Bears undergo hyperphagia, or excessive eating, in late summer and autumn to build fat reserves for winter hibernation, which can lead to a significant increase in body mass, with some bears gaining up to 50% of their body weight.
Food availability and quality directly influence a bear’s ability to accumulate and maintain weight. Areas with abundant high-calorie food sources, such as salmon runs for coastal brown bears, allow individuals to grow larger than those in food-scarce environments. Geographic location and local environmental conditions also lead to variations within a species, with some subspecies or populations growing larger due to factors like climate and food access. For instance, black bears on the East Coast of North America are heavier than those on the West Coast.
Record-Breaking Weights
While average weights provide understanding, some individual bears have achieved exceptional sizes, establishing records for their species. The heaviest polar bear recorded was a male shot in Kotzebue Sound, northwestern Alaska, in 1960, weighing an astonishing 1,002 kilograms (2,209 pounds). This immense individual stood 3.39 meters (11 feet 1 inch) tall on its hind legs.
Kodiak bears, a brown bear subspecies native to Alaska’s Kodiak Archipelago, are known for their size and can rival polar bears in bulk. The largest recorded wild male Kodiak bear weighed 751 kilograms (1,656 pounds). A captive Kodiak bear named Clyde, at the Dakota Zoo, reached 966 kilograms (2,130 pounds) at his death in 1987, and was estimated to have weighed close to 1,089 kilograms (2,400 pounds) a year prior. These extreme weights highlight the upper limits of bear size, often influenced by abundant food and, in some cases, captive conditions.