Context-dependent contributions to sentinel behaviour: audience, satiation and danger effects

Abstract

In group-living species, particularly cooperative breeders, all group members contribute to various behaviours but there is considerable variation between and within individuals in their contributions. While it is well established that there is variation due to differences in the costs and benefits for individuals of different sex, age and dominance status, shorter-term social, internal and environmental factors are also likely to be important. Sentinel behaviour, where individuals adopt a raised position to scan for danger while groupmates forage, offers an opportunity to test hypotheses about context-dependent differences in contributions to group behaviour. Here we used field experiments to manipulate the conspecific audience, satiation state and perceived danger level of dwarf mongooses, Helogale parvula, to investigate how sentinel contributions are modulated by individual context. In addition to standard measures of sentinel behaviour (likelihood of becoming a sentinel, number of bouts, bout duration), we considered within-bout behaviour in terms of surveillance calls and attentiveness (head-scanning rate and distraction levels). We found that the presence of a neighbouring forager (audience) decreased sentinel contributions, while individuals increased their sentinel investment when satiated and experiencing an increased danger level. Changes in head-scanning rate provided evidence for an interaction between the effect of satiation and danger levels, demonstrating that sentinel attentiveness was influenced by changes in context. Our results demonstrate that sentinel behaviour is strongly context dependent, with effects seen in initial bout and bout quantity decisions, as well as within-bout characteristics, and that individual contributions to group behaviours can vary depending on social, internal and environmental factors.