Dallmann, R. & Geissmann, T. (2001). Individuality in the female songs of wild silvery gibbons (Hylobates moloch) on Java, Indonesia. Contributions to Zoology 70: 41-50.
Robert Dallmann & Thomas Geissmann
Institute of Zoology, Tierärztliche Hochschule Hannover, Germany
Key Words: Hylobates moloch; silvery
gibbon; song; individuality; vocalization; Hylobates agilis; Hylobates
klossii.
Abstract: This is the first study comparing individuality in the songs among
several gibbon species. All gibbon species produce loud, long and elaborate song
bouts in the early morning. Silvery gibbons (Hylobates moloch) differ from
other hylobatids, however, in that duet song bouts are absent, male singing appears
to be uncommon and most song bouts are female solo songs. Consistent individual differences
easily distinguish neighboring females in the field, and it has been suggested that
female individuality is particularly high in H. moloch in order to compensate
for the lack of a family-labeling male song. The present study aims to test this
hypothesis by quantifying individuality in H. moloch and comparing it with
data on song individuality in two other gibbon species, H. agilis and H.
klossii, available from earlier studies (Haimoff & Gittins, 1985; Haimoff
& Tilson, 1985). Those studies had been focusing on the great call (i.e. the
most stereotypical song phrase produced by gibbon females) and had determined individual
variation of several variables (such as duration and frequency range of selected
great call notes). We exactly replicated each of those studies with great calls of
H. moloch which were tape-recorded in Ujung Kulon and Gunung Pangrango. According
to the working hypotheses, individuality should be highest in H. moloch lower
in H. klossii (male singing is common) and lowest in H. agilis (male
singing and duets are common). Results: We found a statistically significant degree
of inter-individual variability in most great call variables of H. moloch,
which is higher than that of H. klossii, but lower than that of H. agilis.
Our results do not support the hypothesis that H. moloch females compensate
the rarity of male song contributions with an elevated degree of individuality in
their singing. Instead, we suggest that the amount of great call individuality may
be compromised by the amount of a trill component exhibited by various species of
the lar group of gibbons.
Site by Thomas Geissmann.
For comments & suggestions, please email to
webmaster@gibbons.de
Gibbon Research Lab. Home: |
![]() |