Inheritance of stereotyped gibbon calls

Little is known about how vocal patterns develop in non-human primates, mainly because suitable controlled experiments are difficult to carry out on these animals. Results of isolation experiments and observations of interspecific hybrids suggest no greater role for vocal learning than exists in many other vertebrates, and less than has been found in birds. We have now studied vocal patterns of hybrids between white-handed gibbons (Hylobates lar) and pileated gibbons (Hylobates pileatus) in natural mixed-species groups, in a zone of interspecies contact in central Thailand, and in some captive mixed-species groups. We find that in female hybrids, the patterns of the loud and stereotyped 'great-calls' show no evidence of learning from parents, and appear to be under strong genetic control. Daughters maturing in groups with genetically unlike parents develop great-calls unlike those of their mothers, even though these calls develop only while the daughters sing simultaneously with their mothers.