Science ran a festive piece of research during the longest nights of winter, with biologists who’ve found that male white-tailed deer mark their territory during mating season with antler-rubbings and urine that glows in a faint blue that may be visible to other deer:
“I would equate it to highway reflectors,” says Daniel DeRose-Broeckert, a biologist at the University of Georgia and lead author of the study.
The glow is an example of photoluminescence, a property widely found in nature in which organic material absorbs light and re-emits it at longer wavelengths—shifting ultraviolet (UV) light into our visible range, for example.
…
In the Whitehall Forest in Georgia, he and his colleagues searched for wild white-tailed deer (Odocoileus virginianus) signposts during two periods leading up to the breeding season. They scanned signposted trees, the ground, and urine with UV light in two wavelengths thought to be relatively more abundant at dawn and dusk. Then they measured the light that came back, focusing in on wavelengths that would be picked up by receptors in deer eyes. In total, the team analyzed 146 signposts, including 20 urine patches.
The signposts—both rubbed trees and urine—lit up in a way that would pop out to deer in the dark, the team found. “The urine definitely glows, it looks like spilled white paint,” DeRose-Broeckert says. “It’s pretty striking.” To the deer, the trees and urine may appear as glowing patches of turquoise-blue, he says.
The authors speculate the glow may catch a female’s eye. “You get stimulus from two senses,” DeRose-Broeckert says. “You have the sense of smell telling you something, and then, oh boy, it’s also superbright.”