To gain insight into how great apes communicate, Dr. Mitani will collect field data on all four great ape species - the orangutan, gorilla, chimpanzee, and bonobo (pygmy chimpanzee) - and supplement these materials with recordings already in his possession. Research will be conducted at the Gunung Palung Nature Reserve, West Kalimantan, Indonesia (orangutan), Mahale Mountains Research Station, Tanzania (chimpanzee), Karisoke Research Center, Rwanda (gorilla) and the Lomako Forest, Zaire (bonobo). At each site, animals will be followed and high quality tape recordings of vocalizations will be made. The context in which the calls are uttered will also be noted. Playback experiments will be conducted in which a tape recorded call will be played from a location hidden to the subject animal, and the animal's reaction will be recorded. The research addresses four specific questions. In what ways do great ape "loud calls" differ among species? Do the loud calls of apes vary in acoustic structure over the geographical range of a single species? Are there individual differences in the acoustic structure of loud calls? Is there acoustic variability within the calls of given individuals, and is this variability related to differences in their contexts of emission? All great ape species are endangered and their preservation is a high conservation priority. To do this effectively, it is necessary to understand as much as possible about their behavior, and this research will make a major step in that direction. While it is clear that these species communicate vocally, this process has been studied very little. The work is also important because it will set human language in a broader biological context and possibly provide some insight into how this uniquely human trait developed.
