Blinking as a measurement of group vigilance in red deerCervus elaphusand fallow deerDama dama

Abstract

ABSTRACTThe group vigilance hypothesis suggests animals within a group have a lower overall vigilance level than solitary individuals due to the collective responsibility of predator detection. Previous methods of studying vigilance have used head position as a proxy to indicate a state of vigilance, but it has been suggested that this method is too ambiguous, and the observer cannot accurately ascertain the exact behavioural state of the focal animal. Here, we consider blinking as a proxy for vigilance, as the eye-closure during a blink momentarily reduces the animal’s information about the environment, increasing the risk of unanticipated predator attack. We videoed semi-captive herds of red deerCervus elaphusand fallow deerDama dama, and quantified their blinking behaviour using behavioural logging software. We show that blink rate decreased with increasing group size in both species, suggesting that blinking may be tied with social vigilance rather than anti-predator vigilance. Similarly, the length of the inter-blink interval increased with increasing group size in red deer. Male red deer blinked less than females, and had longer inter-blink intervals, which suggests that blinking may be related to sex-specific behaviour. We discuss the suitability of blinking measures for assessing vigilance behaviour.