Allelomimetic Synchronisation in Merino Sheep
Résumé
Changes between the inactive (resting/ruminating) and active (grazing, walking) states in groups of Merino sheep were studied in the field for different group sizes (two, four, six or eight) of either male or female animals over 6-h periods. The amount of synchrony within groups was high (60–80%) and is attributed to the mutual adjustment of behaviour by group members. To quantify this process, changes in the number of active individuals were fitted by a time homogeneous continuous time Markov chain model. We found that the probability of an individual becoming active increased with the number of active conspecifics in the group and decreased with the number of inactive conspecifics. The reverse effect was found for the probability of becoming inactive. A model of this individual decision-making process is fitted to the data and predictions of the model are shown to account for the synchrony observed within the group. Group synchronization is thus presented as a self-organized dynamic system, where collective oscillations between activity and inactivity arise stochastically from the coupling between individual Markov processes.