Abstract
Although animal societies often evolve due to limited natal dispersal that results in kin clustering and facilitates cooperation among relatives, many species form cooperative groups with low and variable kin structure. To understand how such mixed-kin societies form despite their potential for social conflict, we investigated the environmental causes and subsequent fitness consequences of dispersal decisions in male cooperatively breeding superb starlings (Lamprotornis superbus) living in a climatically unpredictable environment. We show that the two alternative reproductive tactics—natal dispersal vs. philopatry—exhibit reproductive tradeoffs resulting in equal lifetime inclusive fitness. The tactic an individual adopts is governed by the environment its parents experience prior to laying rather than the environment it experiences as an adolescent. When individuals adopt the tactic not predicted by early life environmental conditions, their fitness is reduced. Ultimately, climate-driven oscillating selection may help stabilize mixed-kin animal societies by influencing alternative reproductive trajectories early in life.