Coordination of safe, selfish sentinels based on mutual benefits

Sentinels are group members that watch from prominent positions. Sentinel i nterchanges 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 saf e places to rest because they provide a good view of approaching predators, even if undetected predators preferentially attack sentinels. In pairs, co ordinated sentinel behavior is favored whenever information spreads from a detecting to a non-detecting individual more than half the time. Under thes e conditions, safety for a sentinel produces safety for a forager as a by-p roduct. Thus sentinel behavior occurs for selfish safety reasons but coordi nation of sentinels is based on mutualism. If sentinels can coordinate thei r individual actions, evidence of the game is hidden from view. The fitness consequences of some games may be best indicated by the strategies organis ms take to avoid playing them.