Ring dove males share incubation with females by sitting on the nest for a block of time in the middle of the day. The timing of nest exchanges was studied by experimentally delaying the onset, in the morning, of the male's sitting bout. Such delays induced a concomitant but smaller delay in the offset of the male's sitting bout in the afternoon. The female, however, approached the nest to start her bout of sitting at the usual time in the afternoon even though her previous sitting bout had ended later than usual. These findings, together with data on interactions between the pair at the afternoon exchange, suggest that the behavior of the sitting male reflects an interval timing mechanism initiated with the onset of his sitting bout. In contrast the attempts to regain the nest by the nonsitting female probably reflect a circadian oscillation.