Potential predators elicit alarm calls in many birds and mammals. The context-specific occurrence of acoustically distinct alarm call types may allow conclusions about their functions and/or the underlying call system. Furthermore, many group-living species exhibit a co-operative system of vigilance in terms of predator avoidance. In a descriptive field study I investigated alarm calling and sentinel activity in group-living Arabian Babblers Turdoides squamiceps focussing on the context-specificity of call type occurrence in relation to the caller’s behaviour. The results revealed that two of the three different alarm call types were correlated to the distance to the predator: Barks were uttered more frequently to distant and tzwicks to close predators. Sentinels were more likely to utter barks and trills, but foraging group members tzwicks. Results suggest that sentinels detect potential dangers in greater distances and start calling earlier, whereas foraging birds detect predators only closer and therefore utter higher urgency calls. Finally, the results added to the current knowledge of the urgency-based call system of Arabian babblers, in which information can be provided on different levels: Variation in the call structure of single call types, combined use of different call types and discrete use of different call types in different contexts.
alarm calls, urgency-based call system, sentinel, anti-predator behaviour,Arabian babbler