Multiple antipredator behaviors of sika deer (Cervus nippon) perform various functions depending on social and environmental conditions

Ungulates exhibit a variety of antipredator behaviors serve various functions, such as signaling to predators and conspecifics or directly evading attack or capture. It is currently unclear whether ungulates employ multiple antipredator behaviors depending on social or environmental conditions. To address this issue, we explored the functions of multiple antipredator behaviors of sika deer (Cervus nippon), including whistling, stotting, and rump patch flaring. We conducted direct observations of sika deer responses to a human observer approaching, and examined the effects of group size (solitary or group), signaler’s sex and age (adult male, adult female, or fawn), and season on the occurrence of each behavior. Whistling occurred more often in adult females than males and fawns. This finding suggests that whistling may function as a warning of danger to kin, particularly when used by mothers to alert offspring. The probability of stotting did not differ with group size, signaler’s sex and age, or season, suggesting that this behavior may function as an effective escape gait to avoid predators. Rump patch flaring occurred more often in fawns than in adults, suggesting that flaring may function as a conspecific cohesive signal from fawns to adults. These results suggest that sika deer use multiple antipredator behaviors with different functions depending on the situation.