Foraging in a group potentially allows individuals to reduce anti-predator vigilance without increasing predation risk. Individual vigilance may be further reduced if group members take turns at watching for predators, acting as sentinels or guards. Because the presence or absence of sentinels must be monitored to ensure that the group is guarded at all times, the conditions favouring the evolution of coordinated vigilance are probably very specific. We studied groups of chukars, Alectoris chukar (Gray, 1830) (Phasianidae), a desert species reported to adopt a sentinel system, to see whether this was the case. Individuals identified as sentinels behaved significantly differently from other group members, occupying prominent positions and being vigilant significantly more than foraging group members. The largest individuals became sentinels most frequently, yet were not more vigilant than smaller individuals while they were on guard. Sentinels that ended a bout of vigilance were usually replaced quickly; a soft call was heard during a significant number of exchanges. We conclude that chukars do have a sentinel system of vigilance. A vocalisation, similar to the watchman’s call seen in other species, seems to play a role in coordinating vigilance behaviour.