10:37 Ropoka, still mumbling, moves away from his perch, holding the baby in his right hand, and
goes away from Mkubwa.
10:41 Ropoka tears off some leaves of Cordia millenniiwithin his reach and eats them.
10:48 Mkubwa comes again close to Ropoka to touch occasionally the baby on its back with
his hand.
Ropoka now seemed to eat the baby’s flesh on its right groin. Surprisingly the baby at this stage
was still alive and emitted faintly audible cries.
All at once, chimpanzees around Ropoka became restless. Mkono and Centi climbed down the tree
as Laini, a medium sized male, climbed up. At the same time, Mzee climbed up the tree and crying
loudly, its hair standing on end on the head and shoulders, approached Ropoka.
Now all the chimpanzees in the neighborhood joined in the crying which in turn touched off cries
from all other members of the group separated in three sites in the forest....
Two hours after the author first found them, Ropoka, holding the baby chimpanzee in his mouth,
came down the tree and went away...Others followed him and all soon disappeared (Suzuki
1971: 31–4).Frankie and I had watched the chimpanzees of the Busingiro community for the best
part of a year in 1962 and we had never seen anything like this, so we were exceeding-
ly puzzled when Suzuki sent us a reprint of his paper in 1971. At that time we did not
know that chimpanzees live in mutually exclusive communities, and that the males do
not move from one community to the next but in fact defend their territories fiercely.
Once that fact became known, the rationale for male chimpanzees to practise infanticide
became clearer, if and only if the infant victim had been conceived outside their own
community. But first, they must be clear about this fact, so the question becomes: do
chimpanzees (and other species practising infanticide) know about the relationship
between copulation and pregnancy and birth? Do they know about the length of time
between copulation and birth? (The length of gestation in chimpanzees is roughly seven
and a half months.) Or do they know that a female immigrant into their community who
arrives with an infant is not familiar and has thus conceived with a ‘foreign’ male? And
is this the trigger for their attack on the mother and the killing of her infant?
Infanticide by Sonso males
The first evidence we obtained of an infanticide arose in an unexpected way (Bakuneeta
et al. 1993). On 23 September 1991, Chris Bakuneeta, the Co-director of the Project,
was washing dung through a sieve as part of his Ph.D. study of the feeding ecology of
the Sonso chimpanzees. He was looking for seeds that would later be identified. He
noticed in one faecal sample a large bolus of thin black hairs (approximately 500 hairs,
together with a small piece of bone and cartilage). We considered that this was not the
result of grooming, which can lead to the ingestion of a few hairs but not 500. The hairs
appeared to be from a chimpanzee raising the question of infant-eating. We did not think
they were monkey hairs, also sometimes found in chimpanzee faeces, because of their
black colour and length.
146 Infanticide