Search

It is generally assumed that an individual of a prey species can benefit from an increase in the number of its group's members by reducing its own investment in vigilance. But what behaviour should group members adopt in relation to both the risk of being preyed upon and the individual investment in vigilance? Most models assume that individuals scan independently of one another. It is generally argued that it is more profitable for each group member owing to the cost that coordination of individual scans in non-overlapping bouts of vigilance would require. We studied the relationships between both individual and collective vigilance and group size in Defassa waterbuck, Kobus ellipsiprymnus defassa, in a population living under a predation risk. Our results confirmed that the proportion of time an individual spent in vigilance decreased with group size. However, the time during which at least one individual in the group scanned the environment (collective vigilance) increased. Analyses showed that individuals neither coordinated their scanning in an asynchronous way nor scanned independently of one another. On the contrary, scanning and non-scanning bouts were synchronized between group members, producing waves of collective vigilance. We claim that these waves are triggered by allelomimetic effects i.e. they are a phenomenon produced by an individual copying its neighbour's behaviour. [ABSTRACT FROM AUTHOR]

Several adaptive functions, including gaining information from other group members and detecting predators, are generally ascribed to vigilance in groups of animals subject to predation. Most studies of the effects of neighbors on vigilance have focused on individual vigilance. We investigated the effects of neighbors on vigilance in wild red-necked pademelons Thylogale thetis foraging at night in nonpersistent aggregations in a clearing in rain forest. Neither the total number of pademelons in the clearing nor the numbers at various distances around focal individuals affected the individual vigilance of focal animals. However, focal animals’ individual vigilance did change with the distance to their nearest neighbor and also with distance to cover. Pairs of individuals closer than 10 m apart tended to synchronize their bouts of individual vigilance and foraging. The degree of synchrony within pairs increased with both distance to cover and the total number of pademelons foraging in the area and decreased with increasing distance to the pairs nearest neighbor but did not vary with the distance separating the members of the pair. Thus, despite their individual vigilance being unaffected by the number of other pademelons in the feeding aggregation, pademelons were nonetheless sensitive to the presence of conspecifics and adjusted their behavior in relation to their separation from neighbors. Thus, some vigilance benefits may be obtained from the presence of conspecifics even in species that aggregate only temporarily on food patches without forming more permanent social groups. [ABSTRACT FROM AUTHOR]