Many cooperative breeders forage under predation risks, sentineling is a central activity, and groupmates have to balance between sentineling and foraging. The optimal balance between sentinel activity and foraging may differ among dominant and subordinate individuals, as dominants are more efficient foragers. Two theoretical models pertain to this balance and predict when individuals with different foraging abilities should switch between the two activities on the basis of their energetic state. In one of these models, individuals must attain a critical energetic level by dusk to pass the night, and in the second model fitness is monotonically increasing with the energetic state. We tested these models in the cooperatively breeding Arabian babbler, Turdoides squamiceps. We measured the length of sentinel bouts and the gaps between them both in natural conditions and following experimental feeding. Following feeding ad libitum, subordinates expanded their sentinel bouts significantly more than dominants in comparison with natural conditions. These findings are consistent with the first model, but not with the second. In the experiment, we measured the mass of mealworms consumed by each individual following a sentinel bout relative to its body mass. This ratio was larger for subordinates, indicating that they ended their sentinel bouts at a lower energetic state than dominants. This finding is consistent with the second model, but not with the first. Immediately after eating ad libitum, in 62% of the cases the first behavior performed by the babblers was a new sentinel bout, but in 17% it was a mutual interaction with a groupmate, indicating that social interactions also play a role in the trade-off vis-à-vis sentinel activity.
Bibliographical noteFunding Information:
The study was supported by The Open University of Israel's Research Fund (grant no. 37142). We are grateful for this support.
Funding information The study was supported by The Open University of Israel's Research Fund (grant no. 37142). We are grateful for this support. R.O. is grateful to the Society for Protection of Nature in Israel (SPNI) and Hazeva Field Study Center for hosting the research project. R.O. is also grateful to Avner Anava, Yoel Perel, Amir Kalishow, Yuval Dagay, and Arnon Datner for field assistance. We are grateful to Yaron Sela for his statistical advice. Lastly, we are deeply grateful to Walter Koenig, Sjouke Kingma and to an anonymous referee for their useful and inspiring comments.
© 2019 Blackwell Verlag GmbH
- Turdoides squamiceps
- feeding experiment
- food mass/body mass ratio
- foraging success
- state-dependent sentinel hypothesis