The University of Georgia’s Deer Lab latest study reveals something of a mind-bending revelation from the whitetail woods. According to their findings, as published by our friends over at the National Deer Association, whitetail bucks are cruising through the woods at twilight, guided by rubs and scrapes that glow under UV light like some kind of reflective highway marker. This new visual flex that we humans are unable to see is rewriting a little bit of what we thought we knew about the radiance of the whitetail rut.
Yes, as it turns out, deer aren’t simply sniffing their way through the woods—they’re seeing the world in wavelengths we can’t touch. Unlike humans, whose eye lenses block most UV light below 400 nanometers (nm), deer are about 20 times more sensitive to these wavelengths. Their dichromatic vision, tuned primarily to blue and green, makes them adept at spotting details during crepuscular hours (between dawn and dusk) when UV rays dominate.
Led by graduate research assistant Daniel DeRose-Broeckert under Dr. Gino D’Angelo at UGA’s Warnell School of Forestry and Natural Resources, the study took place in the fall of 2024 at Whitehall Forest, an 840-acre whitetail playground near Athens. The team scoped out 109 fresh rubs and 37 scrapes during pre-rut (early September to early October) and peak rut (mid-October to mid-November).
To isolate the glow effect, researchers worked in pitch-black conditions after sunset, using UV flashlights at 365 nm and 395 nm to mimic crepuscular light. A spectrometer measured the emitted light from rubs, scrapes, and control areas (like plain bark or dirt), with a cardboard shield ensuring precision. They also analyzed chemicals like tree sap compounds (terpenes, phenols) and buck secretions (porphyrins, amino acids) to figure out what made these signs pop.
Daniel DeRose-Broeckert lighting it up | NDA
The results were straight up electric. Researchers soon found that rubs and scrapes don’t just carry scent—they shine through photoluminescence, where UV light triggers compounds to emit deer-visible wavelengths. Background materials like leaves or plain dirt showed no such glow, making these markings stand out like flashing billboards to rutting bucks.
Fresh rubs, especially during peak rut, glowed brightly under 365 nm UV, emitting blue (450 nm) and green (537 nm) wavelengths that align perfectly with deer vision. Trees like black cherry and winged elm, rich in pungent sap, gave off blue-to-purple hues.
“It could be the chemicals produced by removing the bark and exposing the cambium layer, or it could be forehead gland secretions, or it’s both,” DeRose-Broeckert noted. “But either way, there is a glow that is uniquely visible to deer.”
Tree rubs | NDA
As for ground scrapes, pre-rut ground disturbances were a snooze, lacking urine. But peak-rut scrapes, marked with urine on one consistent side (suggesting that bucks approach one side of a scrape exclusively to overwrite rivals), fluoresced a bright, milky white under 365 nm visible even to human eyes like “spilled milk.” These emissions hit deer’s blue-sensitive vision, acting as a clear visual cue.
“I could see the urine in the scrapes with my own eyes,” said Derose-Broeckert. “It looked like spilled milk. What’s cool about it is that the wavelengths produced by the urine in scrapes align very nicely with a deer’s peak visual sensitivity. If a deer did not have a nose, and they walked up to a scrape, they can see how much use it’s getting like it’s spilled white paint.”
Milky ground scrape | NDA
For deer, these glowing signposts are like walkway lighting or highway reflectors, guiding bucks through familiar rut routes at twilight or signaling hot zones for does and rivals.
“This really drives home how appropriate it is to describe these markings as ‘signposts’,” said D’Angelo. “We now know that signposts glow like the neon lights of the Honky Tonk Highway in Nashville.”
Researchers are under the belief that these visual cues serve to aid deer when they are without scent information from the wind and surmise it possible that there are even more environmental features out there that produce a glow unique to the eyesight of whitetail deer.
“The glow of signposts could speed transit of deer like walkway lighting, adorn the woods like holiday lights to ring in the breeding season, serve to intimidate deer like graffiti from rival gangs, and make it easier for deer to locate signposts to check their scent from a distance without having to approach as closely,” D’Angelo noted.
This research reshapes our understanding of deer communication, revealing a vibrant, UV-illuminated world we can’t see. As it turns out, the forest at twilight is a luminescent network of signals, a raw, pulsing system where bucks broadcast status and does pick winners under the cover of darkness. For wildlife enthusiasts and hunters alike, it’s a thrilling reminder that the forest is, in fact, lit.
