RANK AND REPRODUCTION IN THE FEMALE SPOTTED HYENA

Female reproductive success varies with social rank in many gregarious mammals, including primates, ungulates and carnivores. Social groups of spotted hyaenas (Crocuta crocuta) are structured by hierarchical do minance relationships that determine individuals' priority of access t o food and other resources. The influence of female social rank on sev eral measures of reproductive success was examined in a population of free-living Crocuta in Kenya. The study population was continuously ob served for seven years, making it possible to document litter sizes, i nterbirth intervals, ages of cubs at weaning, intervals between weanin g one litter and conceiving the next, annual rates of production of cu bs, and survival of offspring to reproductive maturity. The relationsh ip between availability of food, social rank, and female fertility was examined by monitoring abundance of prey throughout the study period. Most measures of reproductive performance were strongly influenced by social rank High-ranking females began breeding at younger ages, were more frequently able to support pregnancy and lactation concurrently, experienced shorter intervals between litters, and produced more surv iving offspring than did lower-ranking females. Low-ranking females ex hibited better reproductive performance when prey animals were abundan t than when prey were relatively scarce. By contrast, reproductive per formance among high-ranking females was always superior to that exhibi ted by low-ranking females, and did not vary with prey abundance. Fert ility among high-ranking females thus appeared to be less vulnerable t o fluctuations in the food supply than was that among low-ranking fema les.