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Vigilance behaviour in group-living animals helps to detect threats. Individual vigilance levels are thought to decrease as group size or the number of neighbours increases. However, the results of studies on the effects of group size or the number of neighbours are inconsistent, especially in primates. Since social vigilance (i.e. monitoring for group members) plays an essential role in group-living primates, discrepancies among studies may have been caused by differences in the quality of social relationships between group members. Using data from a provisioned group of Japanese macaques, Macaca fuscata , this study examined the effects of the quality of social relationships and the number of neighbours on vigilance levels. We found that the frequency of vigilance was lower when the majority of an individual's neighbours were kin than when kin were in the minority. Since Japanese macaques show strong nepotism and cope with social threats by forming coalitions between close kin, individuals may be able to reduce their vigilance levels by relying on the vigilance of potential allies. Furthermore, when the majority of neighbours were kin, the proportion of time spent on vigilance decreased as the number of neighbours increased. However, when kin were in the minority of neighbours, the number of neighbours did not affect vigilance levels. Overall, our results indicate that the quality of social relationships with neighbours and the number of neighbours interactively affect vigilance levels. • Several social factors affect individual vigilance levels in Japanese macaques. • Time spent vigilant decreased as the number of neighbours increased. • This effect of the number of neighbours exists only if the neighbours are kin. • Vigilance levels may be adjusted depending on the quality of social relationships. [ABSTRACT FROM AUTHOR]

Copying others can be used to enhance foraging and mating opportunities, but can be costly due to the need to monitor the actions of others, which can take time away from foraging and antipredator vigilance. However, little is known about the way animals monitor conspecifics. We investigated the mechanism that European starlings, Sturnus vulgaris , use to visually monitor group mates in perching situations through two questions. First, do starlings copy the timing of each other's vigilance? Second, do they use their centres of acute vision to monitor group mates? We studied a component of vigilance that has received relatively little attention, lateral scans, which consist of changes in the orientation of the head (i.e. gaze shifting) while in a head-up position. We found that starlings copied the timing of their neighbour's scans, placing them closer together in time than expected by chance. This could enhance the speed of social information spread within a group compared to random timing of head movements. The strength of this copying effect varied with neighbour distance and the sex of the follower and leader, suggesting that starlings appear to be more motivated to copy some individuals over others. Additionally, instead of monitoring neighbours with their centres of acute vision (high-quality vision), starlings tended to use their retinal periphery (low-acuity vision), potentially reducing the costs of social monitoring. Copying the timing of lateral scans may have advantages for gathering social information (i.e. quick responses to movements of group mates in situations such as murmurations). However, it can also have costs in terms of delaying the detection of personal information by any group member (e.g. predator attack) due to longer gaps without changes in gaze orientation. Therefore, copying the timing of lateral scans may be restricted to specific contexts (e.g. low predation risk). [ABSTRACT FROM AUTHOR]

Vigilance behaviour is often viewed as a predation avoidance strategy, but animals also use visual monitoring to detect conspecific threats. Studies of social vigilance often consider how group size or nearby conspecifics influence vigilance levels. Less is known about how more specific social variables, such as relative rank and kinship of a subject’s neighbours, affect vigilance of wild animals along with predation risk. To evaluate alternative functional hypotheses for vigilance behaviour, including predator detection and both extra- and within-group conspecific monitoring, we investigated how predation risk and social factors account for variation in vigilance in wild blue monkeys, Cercopithecus mitis, which show strong aggressive competition between groups and mild aggression within them. Studying 18 adult females in two groups, we measured time spent vigilant in 90s focal samples, recording the subject''s activity, microhabitat conditions and identity of neighbours. We used data on dominance ranks and kinship to assess subject-specific social context for each sample. We compared generalized linear mixed models corresponding to each hypothesized function of vigilance, relating variation in vigilance to factors associated with a particular function. The best model related vigilance to predictor variables of all three functions, including recency of an antipredator event, height in canopy, position in forest (edge/interior), recency of an intergroup encounter, number of nearby kin, subject rank and presence of high-ranking neighbours. Overall, most variation in vigilance related to predation risk and between-group competition, while within-group social factors had smaller effects. The range of predictors suggests that vigilance behaviour serves multiple functions, including predator detection and both extragroup and intragroup conspecific monitoring. Species with different social systems might be expected to show different balances of factors that influence vigilance behaviour. [Copyright &y& Elsevier]