Communication tactics among deer are positively glowing, according to new research from the University of Georgia.
A study from the UGA Warnell School of Forestry and Natural Resources found that the mammal's scrapes on the ground and rubs on trees radiate a photoluminescence, or glow, under ultraviolet light.
The glow may help deer to leave messages for potential mates.
"People have been hypothesizing about if this glow exists in the environment, but nobody had gone out yet to try and connect it to the deer until now," said Daniel DeRose-Broeckert, corresponding author of the study and a graduate research associate in the UGA Deer Lab. "As we got closer to breeding season, those markings increased in visibility as deer prepared for it."
Deer signatures emit glow, but only they can see it
Across three months in Whitehall Forest, the researchers searched for deer markings by day and investigated them with UV lights by night.
This is the first study to quantify instances of environmental glowing and connect it to a biological function. In doing so, the researchers analyzed 109 antler rubs on trees and 37 urine-marked scrapes across 800 acres.
In order to see these rubs and scrapes like the deer do, humans need UV lights.
"Their vision is vastly different from ours. Once the sun is slightly gone around dusk and dawn, the UV light dominates for deer since it's not being washed out by the visible light spectrum from the sun," DeRose-Broeckert said.
The glow of the rubs could be a combination of plant and tree sap and secretions from the animal's forehead glands. The scrapes' glow likely comes from urine, the researchers said.
"In the process of scraping the bark off a tree with their antlers, they are depositing glandular secretions. Likewise, when they make a scrape, a different gland is also between their toes," said Gino D'Angelo, co-author of the study and an associate professor in the Warnell School. "Deer have lots of ways to interact with the environment, and they are leaving those signatures out there to smell and glow."
Scrapes, rubs add to previously established deer communication tools
Previous studies suggest other mammals also glow under UV light. But the reason why has historically been unclear.
The researchers believe the glow marks are a visual way deer talk to each other. Deer already use the same scrapes to communicate through scent.
"The scrapes become a communication hub where other deer will visit it after it's created and contribute to it. It's like a phone booth out in the city when trying to make nighttime plans at a meeting point," D'Angelo said.
Marking is extremely key during deer mating season.
"We've known that there's an olfactory component, but now we know the deer are also getting stimulated in two senses, both olfactory and visually. Both males and females utilize scrapes to advertise their presence in the environment and their breeding status and fitness level," DeRose-Broeckert said.
This study was funded by the Warnell School and the UGA Deer Lab. It includes co-authors Billy Hammond, professor in the Franklin College of Arts and Sciences' department of psychology, and Steven Castleberry, professor in wildlife ecology and management.
