Deer markings actually glow | Popular Science
Animals see the world around them in ways that we humans can only imagine. Arctic reindeer’s eyes change color depending on the season to help them find food, while giant squid have eyes the size of dinner plates. Many species take advantage of ultraviolet (UV) light invisible to humans, including deer.
Woodland mammals appear to use UV as a means of communication. Their scratches – marks they make in the dirt or on wood and fill with secretions – glow under the UV light that they can see and we can’t. The same goes for their rubs or the secretion-filled marks their antlers make on trees and fence posts. According to the findings published in the journal Ecology and evolutionphotoluminescence is potentially a way for mammals to find a mate.
“People have speculated about the existence of this glow in the environment, but no one had come out to try to connect it to deer until now,” Daniel DeRose-Broeckert, study co-author and ecologist at the University of Georgia’s Deer Lab, said in a statement. “As we got closer to breeding season, these marks became more and more visible as the deer prepared for them.”
For three months, the Deer Lab team searched during the day for white-tailed deer marks in Whitehall Forest near Athens, Georgia. At night, they examined them with UV lamps. They analyzed 109 antler rubs on trees and 37 urine-marked acres on 800 acres of forest.
“Their vision is very different from ours. Once the sun is slightly gone at dusk and dawn, UV light dominates for deer because it is not erased by the visible light spectrum of the sun,” DeRose-Broeckert said.
The team believes the rub glow may be obtained from a combination of plant and tree sap and secretions from the animal’s frontal glands. The glow from the scratches is probably from urine.
“As they scratch the bark of a tree with their antlers, they deposit glandular secretions. Likewise, when they scratch, a different gland is also found between their toes,” added study co-author and ecologist Gino D’Angelo. “Deer have many ways to interact with the environment, and they leave these signatures to smell and glow.”
Previous studies suggest that other mammals also glow under UV light, but the reasons remain vague. Deer use the same scratchings to communicate by smell. The team in this study therefore believes that the glow offers deer a visual means of communicating.
“The scrapes become a communications center where other deer will visit it after it’s created and contribute. It’s like a phone booth in town when you’re trying to make plans at night at a rendezvous point,” D’Angelo said.
During deer mating season, from mid-October to December, marking is especially important.
“We knew there was an olfactory component, but we now know that deer are also stimulated in two senses, both olfactory and visual,” DeRose-Broeckert said. “Both males and females use scratches to announce their presence in the environment, their reproductive status, and their fitness level.”
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