Infanticide and partial cannibalism in free-ranging Coquerel's sifaka (Propithecus coquereli).

: Infanticide has been observed across many primate taxa, but the extent of its occurrence is not fully understood due to difficulty in observation and uneven reporting. Several hypotheses have been proposed to explain why infanticide occurs in primates and whether it benefits some individuals within a social group. Here we report on a case of infanticide, followed by partial consumption of the infant, in a population of Coquerel's sifaka (Propithecus coquereli) at Mariarano, Northwest Madagascar. We witnessed an adult male sifaka kill and consume part of an infant, a member of his own social group, as well as the mother's reaction to the infanticide. Following the infanticide, the mother of the deceased infant left the social group after repeated agonistic encounters with the other group members. We evaluate how this event relates to the predictions of four common hypotheses. Further research on Coquerel's sifaka is needed to determine the frequency of infanticide in this species, and in lemurs more generally, because infanticide is currently poorly understood in this taxon.