The American Black Bear (Ursus americanus) is the most widely distributed bear species across North America. Despite its common name, this animal presents a paradox, as a significant portion of its population is not actually black. This variation in appearance is a naturally occurring phenomenon known as a color phase. The term “phase” describes a distinct coat color variation found within a single species.
Defining Color Phase
A color phase, also referred to as a color morph or polymorphism, is a biological concept that describes a genetically determined difference in outward appearance. A bear in a non-black color phase is not a different species, subspecies, or hybrid. It is genetically identical to its black counterparts, with the difference being isolated to the expression of specific pigment-regulating genes. The phase refers strictly to the exterior coat color and does not imply any inherent difference in behavior, diet, or overall size.
Catalog of Bear Colorations
The spectrum of non-black colorations in Ursus americanus is the widest of any North American mammal. The most common alternative is the brown or cinnamon phase, which spans shades from light chocolate to blond. These lighter-colored bears are frequently seen throughout the western portion of the species’ range.
Two other color phases are rare and highly localized. The Kermode Bear, or “Spirit Bear,” is a creamy white phase found primarily in the Great Bear Rainforest of coastal British Columbia. This bear is not an albino, as it retains normal pigmentation in its eyes and skin, but rather a unique expression of a recessive gene. The Glacier Bear, sometimes called the “Blue Bear,” is a silvery-blue or steel-gray phase found in the coastal mountains of southeastern Alaska.
Geographic Distribution and Underlying Genetics
The prevalence of black bear color phases is influenced by geography and the underlying genetics that regulate pigment production. In the dense, humid forests of Eastern North America, nearly all black bears are jet black. This color is advantageous because the high concentration of the dark pigment, eumelanin, makes the fur more resistant to abrasion in brushy undergrowth. Conversely, in the open terrain of the Rocky Mountains and the arid Southwestern United States, over 50% of the bears exhibit the lighter brown or cinnamon phase. This lighter coloration is linked to a missense alteration (R153C) in the TYRP1 gene, which reduces the production of dark pigment.
The lighter coat provides a selective benefit in these sunnier, open habitats by reducing heat stress, allowing the bears to forage longer in direct sunlight. The Kermode Bear’s white coat is caused by a recessive mutation in the MC1R gene. This color provides a hunting advantage; studies show white bears are 35% more successful at catching salmon during the day because their light color is less visible to fish in the water. The blue-gray coloration of the Glacier Bear evolved in isolated populations, where the color may have offered better camouflage against ice and snow during past glacial periods.
Not All Brown Bears Are the Same Species
The existence of the brown and cinnamon color phases often leads to confusion with the distantly related Grizzly or Brown Bear (Ursus arctos). Relying on color alone for identification is unreliable, making physical characteristics the only accurate method for distinguishing the two species.
Shoulder Hump
The Grizzly Bear possesses a prominent, muscular shoulder hump that is completely absent on the Black Bear, whose highest point on its back is typically the middle of the rump.
Facial Profile
Grizzly Bears have a broad face with a concave or “dished-in” profile from the eyes to the nose tip. Black Bears, in contrast, have a straighter, more dog-like facial profile, often described as Roman.
Claws
Black Bears have short, sharply curved, dark claws adapted for climbing trees. Grizzly Bears possess much longer, straighter, and often lighter-colored claws designed for digging up roots and prey.