The sentinel behaviour of Arabian babbler floaters

Roni Ostreiher,Aviad Heifetz

doi:10.1098/rsos.160738

Abstract

The sentinel behaviour of 38 Arabian babbler adult floaters, who lived alone within a territory belonging to a foreign group, was studied and compared with their own sentinel behaviour in the past, when they were group members. All floaters acted as sentinels and uttered ‘alarm calls’. This suggests that sentinel activity is due at least, in part, to selfish motives. Floaters sentinelled less than they did as group members, with the decrease in sentinel activity sharper for ex-dominants than for ex-subordinates. One possible explanation for these differences is that sentinel activity is aimed not only at detecting predators, but also at detecting foreign conspecifics. Within a group, the latter incentive is stronger for breeding dominants than for subordinates, whereas all floaters alike may be trying to detect the owners of the territory in which they were roaming but also to avoid being detected by them. Other possible explanations are that floaters have less time and energy for sentinel activity because they are weaker or because foraging is more difficult in a foreign territory. This may be especially so for dominants who used to enjoy privileged access to food in their group. No significant difference was found in the rate of sentinels' ‘alarm calls’ between floaters and group members, suggesting that their main purpose is predator–prey communication, of which warning groupmates may be a side benefit.

Highlights

In some group-living animals, from time to time, one of the group members climbs up to a high position relative to the surroundings, perches steadily for a while and, to the human observer’s eye, looks around
Sentinel activity of floaters compared with their sentinel activity when they were group members
The sentinel behaviour is apparently aimed at gathering information about changes in the surroundings which may be important for the sentinel: approach of terrestrial predators, approach of aerial raptors, approach of a neighbouring group, presence of floaters, behaviour of group members, changes in food sources, behaviour of other animals which may give hints about predators and food sources, changes in weather as well as possibly other aspects, such as the behaviour of the person who is in their vicinity and observes them

Summary

Introduction

In some group-living animals, from time to time, one of the group members climbs up to a high position relative to the surroundings, perches steadily for a while and, to the human observer’s eye, looks around. If a predator is approaching, the observer utters special calls. Other group members stop foraging immediately and escape into dense vegetation or climb to nearby treetops and start calling.

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Conclusion