Coordination of safe , selfish sentinels based on mutual benefits

Sentinels are group members that watch from prominent positions. Sentinel interchanges often appear orderly and the number of sentinels changes little despite the turnover of individuals. I modeled why solitary individuals or group members might take up prominent positions. Such positions can be safe places to rest because they provide a good view of approaching predators, even if undetected predators preferentially attack sentinels. In pairs, coordinated sentinel behavior is favored whenever information spreads from a detecting to a non-detecting individual more than half the time. Under these conditions, safety for a sentinel produces safety for a forager as a by-product. Thus sentinel behavior occurs for selfish safety reasons but coordination of sentinels is based on mutualism. If sentinels can coordinate their individual actions, evidence of the game is hidden from view. The fitness consequences of some games may be best indicated by the strategies organisms take to avoid playing them.