Call of duty? Variation in use of the watchman's song by sentinel dwarf mongooses, Helogale parvula

Social information is invaluable in assessing the need for antipredator behaviour. Individuals can acquire such information by observing the behaviour of others, but reliance on visual cues may be undermined by visual obstructions and social monitoring is often incompatible with foraging. Vocal communication does not require the close proximity of senders and receivers or the suspension of other activities, and there is increasing evidence that foragers can use vocalizations to inform decisions about their own vigilance. However, less work has focused on what factors influence signallers in this context. We used detailed behavioural observations and a playback experiment manipulating perceived risk to investigate the calling behaviour of dwarf mongoose sentinels. Sentinels vocalized more often in dense habitats and when foragers were further away, when visual cues were less likely to be useful. Sentinels also vocalized more in situations most advantageous to others, including when groupmates were likely to be distracted (e.g. when babysitting or foraging) and following an alarm call; sentinels may provide an ‘all clear’ signal. Call rate was reduced in high-risk situations, such as immediately after an alarm call. Individuals of different age, sex and dominance status varied in their likelihood of calling and their response to situations of similar risk, probably because of different cost–benefit trade-offs for separate classes. Our study offers strong evidence that dwarf mongoose sentinels are adjusting their vocal behaviour both to enhance the likelihood that groupmates are aware of their presence and to provide potentially valuable social information about current risk.

► Sentinels provide valuable social information about current risk.
► Sentinels adjust vocal behaviour according to ecological and social conditions.
► Sentinels vocalize when visual communication is impaired.
► Following an increase in perceived predation risk sentinels vocalize more.
► Sentinels reduce call rate in high-risk situations.