Rapid Change in Offspring Sex Ratios After Clan Fission in the Spotted Hyena

We describe the rapid reversal in juvenile sex ratio that occurred after fission of our study clan of free-living spotted hyenas (Crocuta crocuta). Juvenile sex ratios were strongly male biased before fission, when clan size was at or slightly above the habitat's carrying capacity (K). Clan size after fission fell below K, and juvenile sex ratios became female biased within a single reproductive cycle. The change in juvenile sex ratio appeared to be due to altered sex bias in cubs recruited through births. The observed change in secondary sex ratio was only significant among offspring of high-ranking females. Our observations were consistent with predictions of existing sex allocation theories based on local resource competition and enhancement. Our data suggest secondary sex ratios in spotted hyenas are influenced by conflicting demands of competition and cooperation among philopatric individuals.