Why Do Some Black Bears Have Brown Fur?

New research pinpoints the 9,000-year-old genetic mutation that gives some black bears a cinnamon-colored hue

Cinnamon-colored black bear
A cinnamon black bear JT Humphrey / HudsonAlpha

As their name suggests, many American black bears have black fur—but not all of them do. These mammals actually come in a range of hues, from sandy blonde to rusty copper to bluish-grey.

Researchers are particularly interested in why some of these bears have evolved to have cinnamon-colored fur, which makes them look similar to grizzly bears (also known as brown bears). From a safety perspective, it’s important for humans to distinguish between these two species so they know how to respond in an encounter.

In a new paper published Friday in the journal Current Biology, researchers reveal they are one step closer to unraveling the mystery of these look-alike bears. The reddish-brown hue of some black bears likely comes from a genetic variation, the study suggests.

After analyzing DNA samples from 151 black bears living across Canada and the United States, scientists identified a mutation in a gene called tyrosinase-related protein 1, or TYRP1. The mutation changes the amino acid building blocks of the gene, which leads to a bear’s fur appearing either more blackish-brown or more reddish-yellow.

The mutation in black bears is similar to the one that causes albinism in humans, which is often accompanied by pale skin, light-colored hair and, at times, poor eyesight. The cinnamon-colored bears, however, do not appear to have any issues with their eyesight, which would make it more challenging for them to survive.

The mutation is relatively young, in evolutionary terms. The findings suggest it first occurred around 9,360 years ago and has been spreading via breeding ever since.

American black bear sitting in green brush
Many American black bears are black, but some are blonde, brown or bluish-grey. Thomas Fuhrmann via Wikimedia Commons under CC BY-SA 4.0

Today, cinnamon-colored bears live primarily in western states like Idaho, Nevada and Arizona. Bears residing elsewhere—such as on the East Coast or along the Great Lakes—are less likely to have cinnamon-colored fur, because not many bears of that hue have ventured to those areas to spread their genes.

“Geography definitely plays a part,” says study co-author Emily Puckett, a biologist at the University of Memphis, to Live Science’s Jennifer Nalewicki. “The bears don't pass through the Great Plains. If they wanted to go east, they would have to go up north to Canada, across the Canadian [Prairies], around the Great Lakes and then drop back down into the eastern populations. That would take a long time.” While this sort of spreading does occur, it’s a slow process.

Black bears are expanding their range, in part due to advancing protections for the species, including reforestation of their habitat, bear reintroduction programs and tighter hunting regulations, Oklahoma State University ecologist Sue Fairbanks, who was not involved in the study, tells the New York Times’ Sam Jones. As a result, it’s important to keep educating people about these bears’ coloration, she tells the Times. “We have to keep reminding people that black bears can be brown.”

The researchers also explored why the mutation has persisted—what evolutionary benefit does it provide? They tested two possible theories. One suggested the cinnamon-colored fur may help bears regulate their body temperature, and the other posited the hue arose to mimic the appearance of grizzly bears. The data did not support either hypothesis, however.

Instead, the researchers now suspect that having a cinnamon-colored coat may help the bears avoid predators by blending in with their surroundings, especially in southwestern states. This phenomenon, known as crypsis, is also responsible for the bold black-and-white coloration of giant pandas, reports the Times. The black fur helps pandas blend in with dark tree trunks and other shady parts of their environment, while the white fur can help camouflage them against snow and leaves.

Blending in likely helps prevent black bear cubs from becoming a meal for predators, such as bobcats, wolves and mountain lions. And on the flip side, as Rachael Funnell writes for IFL Science, black bears are “omnivores who forage as well as hunt, so it may be that being a toasty cinnamon morph makes it easier to sneak up on things in the forest.”