Infanticide is the killing of offspring by another member of the same species and occurs in many vertebrate groups. Although both males and females commit infanticide, sexually selected infanticide by males has been the primary focus and infanticide by females is less well understood. The goal of this study was to explore the prevalence and function of infanticide in spotted hyenas (Crocuta crocuta) using 30 years of data collected from several social groups in Kenya. These carnivores live in mixed-sex matrilineal groups structured by rigid dominance hierarchies and maintained by social alliances. They breed year-round and raise their cubs in communal dens with other mothers from the same social group. We tested the exploitation hypothesis, which posits that infanticide functions as predation where juveniles are treated as prey. This hypothesis predicts that infanticide would occur most frequently during times of prey scarcity, that cubs and killers would be both male and female, and that killers would eat the victims. Conversely, the social competition hypothesis posits that infanticide is a form of competition among group members over social status and predicts that infanticide would target females (because males leave the social group) and be perpetrated by high-ranking females against low-ranking juveniles.
Results/Conclusions
In reviewing sources of mortality in juveniles from a three-decade study, we found that infanticide accounted for 21.2 % of mortality with known sources experienced by juvenile spotted hyenas. This suggests that infanticide should be further explored as an important factor in hyena natural history. Victims were equally likely to be male or female, but in all observed cases the killers were adult females. Killers were on average higher-ranking than the mothers of victims (t= -2.84, df = 18.903, p = 0.011). Killers ate the body of the victim in some cases, but other times left the cub to be eaten or groomed by other group members. Additionally, infanticide was not more associated with prey availability than other mortality sources (X2=0.846, df = 1, p = 0.358). We conclude that infanticide in this species likely serves as a form of social competition among matrilines, showing the potential tradeoffs to rearing offspring in a social environment. Our results indicate the power of using long-term data to study rare or difficult-to-observe phenomena that may not be the focus of an ongoing study.