Assessment of Sika Deer (Cervus nippon) Visual Acuity Using Landolt Rings

Sika deer (Cervus nippon) cause substantial economic losses in the Japanese agricultural sector. To control animal behavior, knowledge of the sensory and behavioral characteristics of the target animals is necessary. Therefore, to develop effective strategies, we investigated the visual acuity of sika deer (one male and one female) through an operant conditioning experiment. Within a 4 × 8 m closed room, we presented one deer with a positive stimulus (Landolt ring) and a negative stimulus (ordinary ring) on a pair of panels (0.8 × 0.6 m) positioned at a distance of 3 m. Visual acuity was determined by varying the size of the ring. Each session comprised 20 trials, with the criterion for successful discrimination being a minimum of 75% correct choices by the end of the session over three consecutive sessions (P < 0.05, chi-square test). In the discrimination experiment, they were found to be able to discriminate the Landolt ring from the ordinary ring with visual acuities of 0.02, 0.04, 0.08, and 0.16. However, they were unable to distinguish between these rings at a visual acuity of 0.24. Thus, our findings indicate that sika deer have a visual acuity of up to 0.16, comparable to that of sheep. Published online 6 December, 2024; Print publication 31 January, 2025