Does sentinel presence improve foraging success? A study in a cooperative breeder

In various cooperative breeding species, a group member often sentinels from a prominent position that enables early detection of approaching predators and then utters alarm calls to which the other group members react immediately. We tested in the cooperatively breeding Arabian babbler (Argya squamiceps), whether in the presence of a sentinel the other group members forage for longer or more effectively. In natural observations, at different distances from the shelter and in different group sizes, we found no effect of sentinel presence on foraging time. Likewise, in a giving-up density (GUD) experiment with artificial food patches containing mealworms at each of three different distances from the shelter, fewer mealworms were consumed further from the shelter, irrespective of whether a sentinel was present or not during foraging. While foragers react to a sentinel’s alarm calls when a predator approaches, our findings indicate that Arabian babbler foragers do not improve their foraging efficiency due to the sentinel's presence. Combined with previous studies on the Arabian babbler, these findings reinforce the conclusion that in this species the sentinel is 'selfish' and benefits from early detection of predators. These results contrast with those from other cooperative breeders in which sentinels utter calming calls and foraging efficiency increases when sentinels are present. We, therefore, suggest that similar sentinel behaviour may serve different sentinel systems and functions in different cooperative breeders.

Methods
Data were collected in field observations as well as throughout an experiment. The raw data are presented in two files: one for the natural observations and the second for the experiment. Data were analyzed by R, and R codes were presented.