Effect of group size and experience on the ontogeny of sentinel calling behaviour in meerkats

Abstract

Increased vulnerability to predation results in young individuals of many species experiencing higher predation pressure than adults. Consequently, the production of antipredator-related calls by young can differ from that of the same vocalizations given by adults. Sentinel behaviour is a coordinated vigilance behaviour, where one individual climbs on an elevated position and scans the surroundings for predators, while the rest of the group is mainly foraging. Meerkat, Suricata suricatta, sentinels produce six distinct sentinel call types, which inform other group members about the perceived predation risk, resulting in the adjustment of personal vigilance behaviour in foraging group members. Here, we investigated the onset of sentinel behaviour and the ontogeny of the different sentinel call types as well as the development of individual vocal signatures in meerkats. We found that meerkats started acting as a sentinel around 200 days of age, but this was highly dependent on group size, with individuals from smaller groups exhibiting sentinel behaviour earlier than individuals from larger groups. All six sentinel call types were already present in the repertoire upon first emergence of the behaviour; however, call rates of ‘all-clear’ calls increased while ‘warning’ calls decreased with increasing experience as sentinel. Analysis of one of the most frequent sentinel calls, the double note calls, indicated that fundamental frequency, mean amplitude, duration and entropy differed consistently between individuals, but we found no effect of age. Rather, our results provide evidence that individual signatures in this call type were already developed when young meerkats first started to act as sentinel and changed little with age. To conclude, we showed little ontogenetic change in overall sentinel behaviour as well as in its vocal coordination, indicating potentially high selection pressures on antipredator behaviours, such as the sentinel system, resulting in consistent behavioural responses upon first emergence.