The higher the better: sentinel height influences foraging success in a social bird.

School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK.
Proceedings of the Royal Society B: Biological Sciences (Impact Factor: 5.29). 05/2009; 276(1666):2437-42. DOI: 10.1098/rspb.2009.0187
Source: PubMed

ABSTRACT In all social species, information relevant to survival and reproduction can be obtained in two main ways: through personal interaction with the environment (i.e. 'personal' information) and from the performance of others (i.e. 'public' information). While public information is less costly to obtain than personal information, it may be inappropriate or inaccurate. When deciding how much to rely on public information, individuals should therefore assess its potential quality, but this possibility requires empirical testing in animals. Here, we use the sentinel system of cooperatively breeding pied babblers (Turdoides bicolor) to investigate how behavioural decisions of foragers are influenced by potential variation in the quality of anti-predator information from a vigilant groupmate. When sentinels moved to a higher position, from where their probability of detecting predators is likely to be greater, foragers reduced their vigilance, spread out more widely and were more likely to venture into the open. Consequently, they spent more time foraging and increased their foraging efficiency, resulting in a profound increase in biomass intake rate. The opposite behavioural changes, and consequent foraging outcomes, were found when sentinels moved lower. A playback experiment demonstrated that foragers can use vocal cues alone to assess sentinel height. This is the first study to link explicitly a measure of the potential quality of public information with a fitness measure from those relying on the information, and our results emphasize that a full understanding of the evolution of communication in complex societies requires consideration of the reliability of information.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Sentinel behaviour, where individuals take turns to watch for danger and give alarm calls to approaching predators, has been observed in a number of animal societies. However, the evolutionary causes of this behaviour remain unclear. There are two main, competing hypotheses regarding the evolution of sentinel behaviour. The first hypothesis is that it is a cooperative behaviour, where group members benefit from the detection of danger but share the workload of acting as a sentinel. The second is that it is a safe, selfish behaviour. Under the second hypothesis, once an individual is satiated, being a sentinel is safer because sentinels can detect threats more readily and can therefore escape from predators faster. We examined whether sentinels are safer than foragers in a wild, free-living cooperative bird (the pied babbler, Turdoides bicolor) with a well-described sentinel system. We found that sentinel behaviour was costly because (1) sentinels were targeted by predators more often, (2) they were further from cover than foragers, and (3) they took longer to reach the safety of cover following a predator alarm. These results suggest that individuals do not become sentinels because it is safer. This is the first study to demonstrate that sentinels are at greater risk of predator attack than foraging group members and suggests sentinel activity may have evolved as a form of cooperative behaviour.
    Animal Behaviour 01/2013; 85(1):137-142. · 3.07 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Highlights ► Sentinels provide valuable social information about current risk. ► Sentinels adjust vocal behaviour according to ecological and social conditions. ► Sentinels vocalize when visual communication is impaired. ► Following an increase in perceived predation risk sentinels vocalize more. ► Sentinels reduce call rate in high-risk situations.
    Animal Behaviour 05/2013; 85:967-975. · 3.07 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ecological conditions can influence decisions relating to antipredator behaviour through impacts on the likelihood of detecting predators and the ability to hear vocalizations. Previous studies of antipredator behaviour have tended to focus on foragers, whose vigilance behaviour may be confounded by the type of food they are eating, and on receivers in vocal communication networks. We examined the impact of habitat and wind conditions on the behaviour of sentinels, individuals that suspend their own foraging to adopt a raised position to scan for danger while groupmates continue feeding, and that produce a variety of calls used by foragers to adjust their antipredator behaviour. Sentinels of the pied babbler, Turdoides bicolor, a cooperatively breeding bird, started guarding sooner and guarded for longer in long grass compared to more open habitats, and also initiated sentinel bouts sooner in high wind, probably because of the increased predation risk in such circumstances. Sentinels also selected positions that were both lower and closer to the foraging group when it was windy, potentially improving transmission of vocal signals that are valuable to foragers. Our results demonstrate that sentinel behaviour can be influenced by extrinsic factors, as well as the intrinsic factors previously shown, and suggest that ecological variation may affect decisions bearing both selfish and cooperative benefits.
    Animal Behaviour 12/2011; 82(6):1435-1441. · 3.07 Impact Factor


Available from
May 21, 2014