Title: Wild chimpanzees produce community-specific calls: a case for
vocal learning?

Authors: Catherine Crockford (principal author), Ilka Herbinger, Linda
Vigilant and Christophe Boesch

Address for all authors: Max Planck Institute for Evolutionary Anthropology.

Email address: crockford@eva.mpg.de 

Vocal learning, where animals can modify the structure of their
vocalizations as a result of experience, has been found in a range of
birds and mammals.  Although vocal learning is a fundamental aspect of
developing spoken language, there is as yet little evidence that vocal
learning occurs in primates (Hauser et al, 2002).  Here we examine
whether vocal learning may occur in chimpanzees. 

We analysed whether wild male chimpanzees, Pan troglodytes verus, of
four communities living in a similar habitat in the Taï Forest, Côte
d’Ivoire, developed community specific pant hoots.  If so, we expected
males of three contiguous communities to have distinct pant hoots, while
pant hoots of males from a fourth, distant community, located 70km away,
should only differ from those of the contiguous communities by chance. 

Our analysis confirmed these expectations.  In addition, the acoustic
distances between the pant hoots of pairs of individuals did not
correlate with the genetic relatedness of those pairs, where genetic
relatedness was determined using nuclear DNA analysis.  Thus, neither
habitat nor genetic differences accounted for the observation that there
were acoustic differences in the pant hoot structure of males living in
neighbouring communities, but not in those of males from a distant
community.  This suggests that chimpanzees may actively modify pant
hoots to be different from their neighbours, providing support for the
vocal learning hypothesis.  The implications of these results in terms
of the evolution of spoken language will be discussed. 

Reference

Hauser, M.  D., Chomsky, N.  and Fitch, W.  T.  2002.  Science, 298,
1569-1579.