The resilience of an individual to environmental change depends on its ability to respond adaptively. Phenotypic flexibility, i.e., reversible phenotypic plasticity, is such an adaptive response, which has been predicted to evolve in unpredictable environments. We present data on the environmental predictability for 17 generations of socially flexible African striped mice Rhabdomys pumilio, which can switch from group living to solitary living and back to group living. Population density during the breeding season is the main predictor of social organization in striped mice, which become solitary breeding when population density is low and plural breeding when population density is high. Using time series analysis, we could not reject randomness for the variation in population density and found a 6-year cycle for food availability. However, food availability when individual females grew up did not predict the environmental conditions during which they bred in the next year, their only breeding season. Group size was predictable and most females bred plurally in communal groups. However, single breeding is the preferred tactic to avoid infanticide but for single breeding females, it was not predictable from the environment in which they grew up whether they would become single breeders in the next breeding season. Our study indicates unpredictability in the factors most important for determining the optimal breeding tactics for 322 female striped mice. In sum, striped mice exhibit social flexibility in an unpredictable environment, making it an adaptive trait.