Rare white bison calf sighted in Yellowstone National Park, likely due to leucism.

A rare white bison calf has been photographed in Yellowstone National Park, prompting excitement and questions about its origin. Leucism, not albinism, is the likely cause of the calf's unusual color, as leucistic animals lack some cells that would otherwise produce melanin, the pigment that gives color to fur, eyes, feathers, and skin. The calf's body may appear almost entirely white or have white patches, and it typically has normal or dark-colored eyes.