This past June, a rare creature was spotted in Yellowstone National Park in Wyoming: a white bison calf. Only one in a million bison are born with white fur instead of their normal brown.

According to park biologists, the calf’s coloring was likely caused by a genetic mutation. This changed its DNA—the molecule that carries hereditary information. As a result, its body produces less of the pigments, or colored compounds, that would normally be in its fur.

The calf’s appearance is particularly significant to Native American tribes from the region. White bison frequently appear in their folklore and traditional stories. For the Lakota Nation, a white calf’s arrival is “a blessing and a warning,” said Dallas Gudgell from the Buffalo Field Campaign, an organization devoted to bison conservation. “It means that we need to pay more attention to our relationship with the natural world.”