Deer can perceive ultraviolet light, and recent findings indicate they too might leave behind a glowing trail visible within that same light spectrum. This discovery sheds entirely new light on how deer interact socially and how they process their surroundings. The outcomes of this new study have been published in the journal Ecology and Evolution.
Male white-tailed deer (Odocoileus virginianus) are known to leave marks throughout the forest during the autumn rut. They rub their antlers against trees and the forest floor, shedding the velvety covering of their antlers—the soft, blood-rich “velvet” skin covering the hardened bone as it grows—and depositing scent markers via glandular secretions, urine, and feces.
These markers, referred to as “deer rub marks” (on woody vegetation) and “scrapes” (on the ground), function as indicators of a deer’s presence for other cervids: a warning signal to rivals and an advertisement for prospective mates.
However, it turns out that olfaction is not the sole avenue through which deer communicate.
Researchers from the University of Georgia (UGA) in the United States discovered that these markings exhibit a glow in the UV range, which prior research established deer eyes are capable of detecting.
“The resulting photoluminescence would be visible to deer, based on previously documented aspects of their vision,” the investigators state.
This marks the first occasion that scientists have documented evidence of any mammal actually utilizing photoluminescence within its natural habitat, even though UV-induced photoluminescence in mammals has been a subject of study for over a century.
Furthermore, the research satisfies the majority of the criteria necessary to assert that the photoluminescence serves a genuine biological purpose.
Daniel DeRose-Brooks, from the University of Georgia, and his team conducted their study within the 337-hectare Whitehall Forest, an area inhabited by wild deer populations.
During two site surveys, each lasting approximately a month in the autumn of 2024, the team located signs of these deer markings—109 rub marks and 37 scrapes—and revisited each site at night using UV flashlights peaking at 365 nm and 395 nm.
Both of these wavelengths are abundant in the sky during twilight and dawn, the times when deer are most active. Given earlier studies confirming deer can see reflections or emissions at these wavelengths, anything glowing brightly under these lights would be easily visible to a deer’s eye.
As an indirect measure, the scientists employed an instrument designed to quantify illumination—the amount of light being reflected or emitted at each wavelength from a specific spot.
“The rub marks and scrapes containing urine, when exposed to 395 nm and 365 nm radiation, registered higher mean emission intensity values (i.e., appeared brighter) than the surrounding environment and exhibited photoluminescence,” the research group reported.
It remains uncertain how much of this glow originates from the trees and shrubs versus residues of deer urine. For instance, deer urine contains porphyrins and amino acids, substances known to become excited when exposed to longer UV wavelengths. Phenols and terpenes secreted from the bucks’ forehead glands are believed to share comparable properties.
When deer damage vegetation, they expose the woody lignin and plant terpenes—compounds also recognized for their photoluminescent qualities.
“Regardless of whether the photoluminescence stems from the secretions of the deer’s frontal glands or qualities inherent to the wood, the fact remains: the rub marks visually contrast with their background in a manner uniquely suited to deer vision,” the researchers observe.
When illuminated by both types of UV flashlights, the photoluminescence emanating from the markers containing deer traces corresponded to the type of glow registered by the deer’s short-wavelength and medium-wavelength cone cells responsible for daylight vision. This, according to the scientists, supports the notion that deer vision is adapted for low-light conditions at dawn and dusk.
Even more remarkably, this suggests that deer are communicating using glowing “bulletin boards” scattered across the landscape that we cannot perceive at all.
What exactly are the deer communicating? Until further behavioral studies are conducted, we cannot know for certain.
“While we did not directly test changes in deer behavior due to the presence of photoluminescence, the scrape intensity correlated with the rise in deer hormone levels, and we know that behavioral shifts occur as the rut progresses,” the researchers conclude.
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