a duration of eighty-six minutes.Songs are preferentially uttered in the
early morning hours,with species-specific preferences for specific hours
before,around,or after dawn.
The songs are stereotyped and species-specific (Marshall and Marshall
1976,1978; Marler and Tenaza 1977; Haimoff 1984; Marshall and
Sugardjito 1986;Geissmann 1993,1995).Species can easily be identified
by their songs (figure 7.3),and vocal characteristics have been used to
assess systematic relationships among hylobatids and reconstruct their
phylogeny (Haimoff et al.1982,1984;Creel and Preuschoft 1984;
Marshall,Sugardjito,and Markaya 1984;Geissmann 1993).
Another specialization is the occurrence of duet singing in all gibbons
with the exception of H.klossiiand H.moloch(Geissmann 1993).Duets
are mostly sung by mated pairs (figure 7.4).Typically,mates combine
their repertoire in relatively rigid,more or less precisely timed vocal
interactions to produce well-patterned duets.105 Gibbon Songs and Human Music
Figure 7.2
Singing male white-handed gibbon (Hylobates lar,Zoo Rapperswil).Fig.7.2