Abstract
Sleep is an important but overlooked component of animal behaviour, especially its social and conservation facets. Here, we use 15 years of data to comprehensively describe the roosting behaviour of cooperatively breeding birds and test hypotheses about its ecological and social determinants. We show that wild Arabian babbler groups in the Arava Desert of Israel preferred roosting in live plants with dense canopies (mostly Acacia tree spp. and reed clusters). Roosting sites were located in the inner areas of territories regardless of territorial conflicts. Groups almost always roosted in intimate huddles but tended to separate into sub-groups that roost in nearby trees as group size increased. Despite the abundance of suitable sites for roosting, each group only used an average of 2.4 main roosting sites within its territory. Social groups thus exhibited strong, non-random fidelity to specific roosting sites that extended over ≥4 group generations and ≥15 years. To the best of our knowledge, this is the longest roosting site fidelity shown for cooperatively breeding birds and mammals. This study stresses the importance of conserving roosting sites of species with strong site fidelity and lays the foundations for advanced sleep research in a highly cooperative species.