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Abstract

Sentinels occupy high, exposed positions while other group members forage nearby. If sentinel behavior involves a foraging–predation risk trade-off, animals should be sentinels more when fed supplemental food. When individual Florida scrub-jays (Aphelocoma coerulescens) were fed fragments of peanuts, during the following 30 min they shifted 30% of their time from foraging to sentinel behavior. In a follow-up experiment, we fed either one or two members in each group. As before, the jays reduced their foraging and spent much more time as sentinels when given supplemental food. In each treatment, pairs were sentinels simultaneously considerably less often than expected by chance. The dramatic shift from foraging to sentinel behavior suggests that for Florida scrub-jays sentinel behavior brings substantial benefits for no greater cost than that of lost opportunities to forage. Because the results held for simple mated pairs of scrub-jays, we argue that kin selection and social prestige are not necessary to explain sentinel behavior.