Vigilance behaviour is more contagious when chewing stops: examining the characteristics of contagious vigilance in bighorn sheep

摘要

Members of a social group must behave similarly for a group to persist. One way for this behavioural similarity to occur is through the contagious spread of behaviours. However, there is significant variation in reported rates of behavioural contagion, and the mechanisms governing the spread of a behaviour from one individual to the next are not clear. Why is a behaviour sometimes contagious to a neighbouring individual, and other times not? Here, we examine the contagiousness of vigilance behaviour in bighorn sheep ( Ovis canadensis ) to determine whether particular characteristics of the vigilance bout affect the probability of contagion. We also investigate whether the vigilance characteristics differ between induced and routine vigilance, and thus might be reliable indicators for the presence of a relevant external stimulus. Results indicate that induced vigilance bouts involve significantly shorter head raise durations, longer first fixed gazes, and higher rates of chewing cessation in comparison to routine vigilance bouts. A fourth variable, looking in single or multiple directions before returning to grazing, did not differ between induced and routine vigilance. Interestingly, chewing cessation was the only one of four variables that predicted whether a vigilance bout would be contagious to a neighbouring sheep. These findings indicate that particular characteristics of a behaviour can affect whether a behaviour spreads to neighbouring individuals. Results are discussed in terms of both attention and learning as potential mechanisms regulating the spread of behaviour between social partners, in addition to providing new insight regarding the potential costs of vigilance behaviour. Significance statement The contagious spread of behaviours is essential for group cohesion and coordination; however, little is known about why some behaviours spread and others do not. Here, we examine whether particular characteristics of a behaviour affect whether it spreads to a neighbouring individual. Using vigilance behaviour in bighorn sheep as our study system, we first demonstrate that the characteristics of vigilance behaviour differ depending on whether the vigilance behaviour was routine or induced (by an external stimulus). We then demonstrate that one of the defining characteristics of induced vigilance (whether an individual ceases chewing at the onset of a vigilance bout) increases the chance of the behaviour spreading to neighbouring individuals. Results suggest that variation in the way that a behaviour is performed can affect how contagious it is.