White-tailed deer are crepuscular, short-day breeders that use rubs and scrapes (i.e., signposts) in the environment to communicate physiological status to conspecifics. Deer optical anatomy and visual capabilities are relatively well-understood including sensitivity to ultraviolet (UV) wavelengths. UV wavelengths are present during crepuscular hours but are not visible to humans. Previous studies have described signposts and their use by deer but quantification of the spectral characteristics, including photoluminescence (i.e., glow resulting from exposure to UV), and how the spectral characteristics of signposts shape deer environmental perception, is unknown. The goal of our study was to quantify the spectral characteristics of signposts, including visibility outside the human visual range and relate our findings to what is known about deer vision. We located 148 signposts (rubs = 110, scrapes = 38) from 8 September – 12 November 2024 in the Piedmont of Georgia. We exposed signposts to 365 and 395 nm UV lights while measuring reflectance/photoluminescence with a telescoping spectral radiometer. We collected spectral data at night to simulate laboratory conditions. We found that the contrast between signposts and the surrounding environment was relatively high including wavelengths outside of the human visual range (based on sources such as urine-based photoluminescence). These data suggest that deer behavior relative to signposts is likely based on visual cues, especially in low light conditions, that are not seen by human observers and gives a new perspective to deer behavior based on visual ecology.
