Greater access to social information is a proposed benefit of group living . However, individuals vary in the quantity and quality of information they provide , and prior knowledge about signaller reliability is likely important when receivers decide how to respond . While dispersal causes regular changes in group membership , no experimental work has investigated social-information provision and use in this context. We studied sentinel behaviour following immigration in a habituated population of wild dwarf mongooses (Helogale parvula) ; sentinels (raised guards) use various vocalisations to provide social information [5,6. Recent immigrants acted as sentinels rarely and significantly less often than residents, limiting their role as social-information providers. Even when recent immigrants acted as social-information providers, foragers responded to them less than they did to residents. Several months after arrival, immigrants had increased sentinel contributions, and foragers no longer responded differently to sentinel activity by former immigrants and residents. Our results raise questions about the assumed social-information benefits associated with increased group size. Greater access to social information is a proposed benefit of group living. However, Kern & Radford use long-term data and field experiments to show that social-information provision and use is lower than expected following dispersal events in dwarf mongooses. Group-living benefits should not be assumed, but may change with social circumstances.