In a short paper, Simon Townsend and colleagues report on several instances of infanticide initiated by female chimpanzees in the Bundongo Forest:
These observations document a systematic pattern of lethal aggression in female chimpanzees. Such infanticidal attacks are neither isolated events by pathological individuals nor mere biproducts of male aggression; they seem to be part of the female behavioural repertoire. In all cases, the remains showed significant bites to the head, almost certainly fatal in two cases, indicating that these were purposeful, not accidental, killings. Equally remarkable, at least one, but possibly more, cases were the result of coalitionary attacks by resident females. While male cooperation in aggressive attacks is well documented for chimpanzees 1 and 2, coalitionary aggression by unrelated females is not.
They speculate that the attacks are related to limited resources: the study group has had a growth in the number of females due to immigration and births, but has not increased as much in the number of males; territorial growth would require a larger male coalition.
Townsend SW, Slocombe KE, Thompson ME, Zuberbüler K. 2007. Female-led infanticide in wild chimpanzees. Curr Biol 17:R355-R356. doi:10.1016/j.cub.2007.03.020