One spring night in Wisconsin, Jon Martin, a biologist, was in his backyard with an ultraviolet flashlight. Suddenly, a hot-pink squirrel flew by.

It was a southern flying squirrel, a small, furry creature most active at dawn and dusk. Under most circumstances, it has a warm brown color. But in the beam of Dr. Martin’s flashlight, it sported a gaudy Day-Glo hue closer to something you might see in a nightclub or a Jazzercise class circa 1988.

“He told his colleagues at Northland College, but of course, everyone was pretty skeptical,” said Allison Kohler, a graduate student at Texas A&M University.

Dr. Martin asked Ms. Kohler, then a student at Northland, to look into it. After examining more than 100 specimens of flying squirrels across two museum collections and spotting five more squirrels under UV light in the wild, the researchers and their colleagues reported surprising results last week in the Journal of Mammalogy: The pink is real.