Recent scientific inquiry has revealed that cervids possess the capacity to perceive ultraviolet light, and further investigation indicates they are also capable of leaving behind luminescent trails discernible within these specific wavelengths.
This groundbreaking revelation offers a novel perspective on inter-cervid communication and their sensory interpretation of their surroundings.
During the autumnal breeding period, male white-tailed deer (Odocoileus virginianus) are recognized for establishing their territorial presence within woodland environments. This practice involves abrading their antlers against arboreal and terrestrial surfaces, shedding the soft, vascularized velvet that envelopes their developing ossified antlers. Concurrently, they deposit olfactory markers comprising glandular exudates, urine, and feces.
These territorial indicators, referred to as ‘deer rubs’ on vegetation and ‘scent-marking scrapes’ on the ground, function as signals to other fauna, signifying a deer’s occupancy — a deterrent to conspecific rivals and an allure to potential reproductive partners.
However, it appears that olfactory signals are not the exclusive mode of cervid discourse.
Researchers at the University of Georgia (UGA) in the United States have ascertained that these territorial markings exhibit luminescence in the ultraviolet spectrum, a finding consistent with prior studies demonstrating the visual acuity of cervid eyes within this range.
“The resultant photoluminescence would be detectable by deer, contingent upon their previously documented visual capabilities,” the research group articulates in their published work detailing this phenomenon.
This represents the inaugural instance of scientists documenting the deliberate utilization of photoluminescence within their environment by any mammalian species, despite the study of UV-induced photoluminescence in mammals having a history spanning over a century.
Furthermore, the investigation addresses the majority of criteria necessary to posit that photoluminescence serves a discernible biological function.
Daniel DeRose-Broeckert, a postgraduate research associate at UGA, and his collaborators conducted their research within an expansive 337-hectare (approximately 840-acre) arboretum designated as Whitehall, a domain where deer populations freely inhabit.
The investigative team located cervid territorial markers—comprising 109 rubs and 37 scrapes—during two distinct survey periods, each spanning roughly one month in the autumn of 2024. They subsequently revisited each site nocturnally, equipped with ultraviolet illumination devices emitting at wavelengths of 365 nm and 395 nm.
Both of these spectral bands are prevalent in atmospheric conditions during twilight and dawn, periods of peak cervid activity. Given that prior research has established cervids’ ability to perceive reflections or emissions within these wavelengths, any substance emitting a pronounced glow under these light sources would be readily apparent to their visual organs.
As a surrogate measure, the scientists employed an instrument designed to quantify irradiance values: the extent of light reflected or emitted at each specific wavelength from a defined locus.
“Urine deposited at scrapes and rubs exposed to 395 and 365 nm displayed superior average irradiance values (indicating greater luminescence) compared to the surrounding substrate, and demonstrated photoluminescent properties,” the team reports.
It remains indeterminate the extent to which this luminescence originates from the vegetal matter versus residual cervid fluids. For instance, cervid urine contains porphyrins and amino acids that become energized when subjected to longer UV wavelengths. Phenols and terpenes exuded from the frontal glands of male deer are presumed to exhibit analogous characteristics.
The physical disruption of flora by deer exposes underlying ligneous lignin and plant terpenes, classes of compounds similarly known to exhibit photoluminescence.
“Irrespective of whether the photoluminescence originates from the glandular secretions of deer foreheads or from botanical constituents, the evident fact is that these rubs present a visual contrast to their surroundings in a manner uniquely tailored to cervid visual perception,” the team observes.
Under both types of UV illumination, the photoluminescence emanating from these cervid markers was of a spectral quality capable of being registered by the photoreceptor cones within a deer’s retina, particularly those attuned to short and middle-wavelength visible light. This observation, according to the researchers, corroborates the adaptation of cervid vision to the dim illumination conditions prevalent at dawn and dusk.
More remarkably, this suggests that deer are engaging in communication through luminescent ‘bulletin boards’ dispersed throughout the forest, invisible to the human eye.
Regarding the specific communicative content conveyed by these signals, definitive understanding awaits further investigative efforts.
“While direct correlation with behavioral modification in response to photoluminescence was not assessed in this study, the observed increase in rub irradiance coincided with elevated cervid hormone levels, and known shifts in behavior are intrinsically linked to the progression of the breeding season,” the team writes.
