The function of sentinel alarm calls in the Arabian babbler

Abstract

In various group-living species, from time to time one of the group members acts as a sentinel and utters alarm calls when detecting a predator. Hearing these calls, other group mates usually react by quickly changing their behaviour. Uttering alarm calls is an anti-predator mechanism with several possible functions. In this study our aim was to assess the function of alarm calls in the Arabian babbler Argya squamiceps, a cooperatively breeding songbird. We observed 10 groups in natural conditions and recorded 1000 reactions of 55 foraging group members to 268 sets of alarm calls uttered by the sentinels. The most frequent reaction of the group members to the sentinel's alarm calls was to stop foraging immediately, to fly up to the closest treetop and to start calling alarm calls. In all the recorded cases, the sentinel remained in place and continued to call. The alarm calls continued as long as the raptor could be seen, and then ceased gradually, after which babblers flew down and returned to foraging. We conclude that the main function of alarm calls in the Arabian babbler is pursuit deterrence. In particular, while foragers benefit from the information content of the sentinel's alarm calls and react on their basis, the raptor is the primary audience addressed by the calls uttered by the sentinel and the foragers who join it.

The shirker’s dilemma and the prospect of cooperation in large groups

“…Alternatively, they can fly up and join the sentinel on treetops in calling toward the raptor. The latter is the typical choice of foragers, constituting more than 80% of foragers' reactions (Ostreiher and Heifetz, 2020). Moreover, even lone Arabian babblers devoid of territory (i.e., "floaters") engage in calling from treetops towards raptors when they spot them (Ostreiher and Heifetz, 2017).…”

The relative contribution of acoustic signals versus movement cues in group coordination and collective decision-making

“…Acoustic communication is also used in another coordinated group activity, sentinel behaviour, which has evolved in some social mammals and birds [31]. Sentinels are individuals stationed in a prominent position that scan for predators and frequently emit specific acoustic signals while the other group members are foraging [32][33][34][35]. Sentinels often give soft surveillance calls, providing information about their presence [35].…”

The biological roots of music and dance: Extending the credible signaling hypothesis to predator deterrence

“…But alarm calls also signal to the predator that it has been detected, which might deter its pursuit, directly benefiting the signaler (Bergstrom & Lachmann, 2001;Ramesh & Mitchell, 2018;Woodland, Jaafar, & Knight, 1980). Many studies now show that alarm calls do deter predators (Hedley & Caro, 2021;Ostreiher & Heifetz, 2020;Woodland et al, 1980). When many monkey species detect leopards, for example, an ambush predator, they give alarm calls.…”