Female chimpanzees can be as ferocious and deadly as males, given the right set of circumstances. Males of the species are infamous for their violent behaviour, but now a gang of female chimpanzees have been spotted killing an infant in Budongo forest in Uganda.
Simon Townsend of the University of St Andrews, UK, and colleagues suspect two other infants met their ends in similar ways.
Infanticide by females has been reported before, notably by Jane Goodall in Gombe, Tanzania. In that case several infants were killed and eaten by a mother-daughter pair. It wasn鈥檛 clear if those killings were the result of pathological behaviour, or if there were other contributory factors. From long-term observations at Gombe, primatologist Anne Pusey of the Jane Goodall Institute Center for Primate Studies at the University of Minnesota, St Paul, suggested that ecological competition may be a factor, and now Townsend鈥檚 team support this interpretation.
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They suggest the infanticide in Budongo was adaptive behaviour because females from the resident community attacked immigrant females and their newborns. Adult males, far from instigating the aggression, tried to defend the infants (Current Biology, vol 17, p R356).
The ratio of females to males has risen dramatically in the Budongo chimpanzee community in the past five years due to the arrival of 13 females, bringing the total to 26. Townsend thinks the resulting ecological pressure has led to infanticidal behaviour. 鈥淔emales are experiencing competition for mates and for food and they鈥檙e responding in a violent manner,鈥� he says.
Pusey says that there is now evidence that female chimps living in good areas with good quality food have more and healthier offspring. That means any new female is competition. 鈥淪he鈥檚 a threat because she might compete for the same areas, so they鈥檙e very aggressive then,鈥� explains Pusey.
Killing the infants removes a competitor when they are very vulnerable, Pusey adds, but says that it takes more than one female to do it. Females often travel with adult males, who protect them and their offspring from aggression by other females.
