Rank and reproduction in the female spotted hyaena

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 dominance relationships that determine individuals' priority of access to food and other resources. The influence of female social rank on several measures of reproductive success was examined in a population of free-living Crocuta in Kenya. The study population was continuously observed for seven years, making it possible to document litter sizes, interbirth intervals, ages of cubs at weaning, intervals between weaning one litter and conceiving the next, annual rates of production of cubs, and survival of offspring to reproductive maturity. The relationship 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 a younger ages, were more frequently able to support pregnancy and lactation concurrently experienced shorter intervals between litters, and produced more surviving offspring than did lower-ranking females. Low-ranking females exhibited better reproductive performance when prey animals were abundant than when prey were relatively scarce. By contrast, reproductive performance among high-ranking females was always superior to that exhibited by low-ranking females, and did not vary with prey abundance. Fertility among high-ranking females thus appeared to be less vulnerable to fluctuations in the food supply than was that among low-ranking females.