Deer Create Mysterious Ultraviolet Signals That Glow in Forests
NEWS | 19 February 2026
Deer have the ability to see ultraviolet light, and a recent study shows they can also leave a glowing trail visible in those wavelengths, too. The discovery casts a whole new light on the way deer are communicating with each other, and how they perceive their environment. Male white-tailed deer (Odocoileus virginianus) are known for making their mark on the forest during their autumn mating season. They rub their antlers against trees and the forest floor, shedding antler velvet – the soft, blood-rich velveteen 'skin' that covers their calcified antlers as they're growing – and leaving scent marks in the form of glandular secretions, urine and poop. These marks, known as 'deer rubs' (on trees and shrubs) and scent-marking scrapes (on the ground), act as signposts to other animals of a deer's presence: a warning to rivals, a catcall to potential mates. But scent, it seems, is not the only language with which the deer communicate. Scientists at the University of Georgia (UGA) in the US have discovered that these marks 'glow' in ultraviolet wavelengths, which previous studies have shown deer eyes are capable of seeing. "The resulting photoluminescence would be visible to deer based on previously described deer visual capabilities," the team writes in their published paper describing the phenomenon. This is the first time scientists have documented evidence of any mammal actually using photoluminescence in their environment, although UV-induced photoluminescence in mammals has been studied for more than a century. What's more, the study checks most of the boxes needed to say whether photoluminescence is actually serving a biological function. frameborder="0″ allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen> Daniel DeRose-Broeckert, a graduate research assistant at UGA, and colleagues carried out their study in a 337-hectare (about 840-acre) research forest called Whitehall, where deer roam freely. The team tracked down deer 'signposts' – 109 rubs and 37 scrapes – during two roughly month-long surveys in the fall of 2024, and returned to each one at night with ultraviolet flashlights peaking at 365 nm and 395 nm. Both of these wavelengths abound in the skies at twilight and dawn, when deer are most active. And since earlier research has shown deer can see reflections or emissions of these wavelengths, anything that glows bright enough under these torches would be easily visible to a deer's eye. As a proxy, the scientists used a tool that measures irradiance values: how much light is reflected or emitted at each wavelength, from a given spot. "Rubs and urine found on scrapes exposed to 395 and 365 nm had greater average irradiance values (i.e., brighter) than the surrounding environment, and exhibited photoluminescence," the team reports. It's unclear how much of this glow comes from the trees and shrubs, and how much is coming from remnant deer fluids. Deer urine, for instance, contains porphyrins and amino acids that become excited under longer UV wavelengths. Phenols and terpenes released from the forehead glands of male deers are thought to have a similar quality. When the deer damage plants, they expose woody lignin and plant terpenes, types of compounds also known to exhibit photoluminescence. "Whether the photoluminescence is the result of deer forehead glandular secretions or wood properties, the fact remains that rubs visually contrast the surrounding environment in a way that is uniquely suited for deer vision," the team notes. Related: Bats in The US Can Glow Ghostly Green, And Scientists Have No Idea Why Under both kinds of UV flashlight, the photoluminescence emitted by the deer signposts was the right kind to be registered by the cones within a deer's eye that are sensitive to short- and middle-wave visible light. This, the scientists say, reaffirms that deer eyesight is adapted to the low-light conditions of dawn and dusk. More impressively, it suggests deer are communicating with light-up 'noticeboards' throughout the forest that the rest of us can't even see. As to what the deer are saying? Until further research is conducted, we won't know for sure. "Though we did not directly test for a behavioral change in deer as a result of the presence of photoluminescence, the irradiance of rubs increased at the same time as deer hormone levels increased, and behavioral changes are known to change with the progression of the breeding season," the team writes. This research was published in Ecology and Evolution.
Author: Jess Cockerill.
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