Discrimination between two chromatic colors in sika deer

Abstract

To clarify animal vision, biochemical, anatomical–histological, neurophysiological and behavioral research using horses, cows, sheep, pigs, and deer have been conducted. Japanese sika deer (Cervus nippon) have caused severe problems in Japan and many devices and repellents that use visual, auditory, and olfactory senses became commercially available to scare away deer from agricultural fields or rail tracks. Development of effective damage mitigation strategies needs more understanding of the senses of deer, especially visual. Ungulates, including sika deer, are dichromatic, with both S- and M-cones; however, the color vision of deer has not been thoroughly investigated. The present study was undertaken to understand the color vision characteristics of sika deer. We evaluated their ability to distinguish between various color combinations. Three captive sika deer were trained in a color discrimination experiment using a two-choice discrimination apparatus. The positive stimulus was always 5B6/8 (blue), and the following six colors were used as negative stimuli: white, 5Y6/8 (yellow), 10G6/8 (green), 10BG6/8 (blue–green), 5RP6/8 (red–purple), and 5BP6/8 (blue–purple) based on the dichromatic color vision confused colors chart. All deer could distinguish blue from white, yellow, and green. No deer could distinguish between blue and red–purple or blue–purple. Some deer could distinguish blue from blue–green, depending on the individual. Humans with protanopia confuse blue with red–purple or blue–purple, so these results suggest that the color vision characteristics of sika deer are similar to those of humans with protanopia. This is the first report discussing the findings of color combinations that are easily visible to deer.