Deer's Secret Signals: A UV Light-Up World

A recent study indicates that deer, capable of seeing ultraviolet (UV) light, also leave a glowing trail visible in these wavelengths. This discovery suggests a new aspect of how deer communicate and perceive their environment.

Uncovering Hidden Communication

Male white-tailed deer (Odocoileus virginianus) create marks in their habitat during the autumn mating season. These marks include rubs, where they rub antlers against trees, and scrapes, where they disturb the ground. These locations contain antler velvet, glandular secretions, urine, and feces. These marks function as signposts, indicating a deer's presence to rivals and potential mates.

The UV Glow Revelation

Scientists at the University of Georgia (UGA) in the US found that these marks exhibit a 'glow' under UV wavelengths, which deer vision is capable of perceiving. The team noted that the resulting photoluminescence would be visible to deer based on previously documented deer visual capabilities.

This research marks the first time scientists have documented evidence of a mammal using photoluminescence in its environment for communication, although UV-induced photoluminescence in mammals has been studied for over a century.

This discovery is a groundbreaking insight, as it marks the first documented evidence of a mammal using photoluminescence in its environment for communication.

The Science of the Illuminated Marks

The study, conducted in Whitehall research forest, involved tracking 109 rubs and 37 scrapes. Researchers used UV flashlights (peaking at 365 nm and 395 nm) at night, wavelengths present during twilight and dawn when deer are most active. Measurements of irradiance values showed that rubs and urine on scrapes exposed to these wavelengths had higher average irradiance values and exhibited photoluminescence compared to the surrounding environment.

The photoluminescence may originate from various sources. Deer urine contains porphyrins and amino acids that become excited under longer UV wavelengths. Phenols and terpenes from male deer's forehead glands may also contribute. Additionally, damaged plants expose woody lignin and plant terpenes, which are known to exhibit photoluminescence. The researchers concluded that regardless of the source, the photoluminescence causes rubs to visually contrast with their environment in a manner suited for deer vision.

Deer's Unique Vision and Forest 'Noticeboards'

The emitted photoluminescence was registered by the short- and middle-wave sensitive cones in a deer's eye, supporting the idea that deer eyesight is adapted to low-light conditions. This suggests deer create light-up 'noticeboards' within the forest, undetectable to humans. While the study did not directly test for behavioral changes in deer due to photoluminescence, the irradiance of rubs increased concurrently with deer hormone levels, and behavioral changes are known to occur during the breeding season.

This research was published in the journal Ecology and Evolution.