Functions of sibling aggression in the spotted hyaena, Crocuta crocuta

Sibling rivalry, occurring in the form of intense aggression directed at siblings, has been described in many birds, but few mammals. In the spotted hyaena, early aggression directed at littermates has been hypothesized to function as a mechanism for litter reduction by siblicide, particularly within same-sex litters. Alternatively, intralitter aggression might serve to establish and maintain a rank relationship between twin littermates. Our goal here was to use long-term observations of 46 litters to test these two hypotheses in wild Crocuta. Rates of sibling aggression were high during the first 2 months of life, but then dropped to low levels. During the first year of life, littermates fought mainly over milk and meat, both of which are critical food resources, and dominant cubs were heavier than subordinate siblings of the same age. Rates at which mixed-sex littermates fought did not differ significantly from fighting rates within same-sex litters. Rates of intralitter aggression were higher when local prey were scarce than when prey were abundant. Although we found no significant effect of maternal social rank on cub aggression rates, our results were consistent with the notion that aggression rates within litters vary with maternal rank. Our results did not support the hypothesis that intralitter aggression functions to mediate siblicide, particularly within same-sex litters. Instead, our results were consistent with the hypothesis that early sibling aggression in Crocuta functions to establish and maintain a rank relationship within the litter.