monogamy and gibbon duets

[M Chuk]

If your student has been studying gibbons for several years she may
already be well aware of anything I might suggest. For possible
recent resources see below. But first ...


The act of singing is common to many species who do not have speech
but who do have communication and, as some may argue, have language
as well. In its broader takes, language, as a system of
signification, need not entail either speech or even reciprocity.
Certainly signing languages serve as examples par excellence and
Barthes' well known descriptions of road signs (Elements de la
semiologie) and clothing (Systeme de la mode) may be considered. But
if one wishes to use 'language' here to describe _human primary
communication that expresses human symbolism_, I have no trouble with
that - provided this does not endorse anthrocentric or biocentric
conclusions that may obscure [further] aniamal research and
recognition and the subsequent development of a more precise
terminology of Other possible symbolic systems.

Birdsong and duet comes to mind, of course. But more pertinent to
this discussion, there are four old world primate groups that not
only produce song, but produce duets that are elaborate and complex.
(This also occurs in similar new world primate groups although I'm
not current on the research.) The evolutionary convergence of these
four very different groups is seen in specific behavioural traits.
They are all monogame and stable (this rare combination occurs only
in these groups; monogame unstable primate groups do not duet); they
all sing in the morning, mostly at or near dawn at similar levels of
the canopy; they are all extremely territorial. One of these groups
is made up of our fourth cousins the hylobates or gibbons. All but
two of the eleven gibbon species sing duets; Siamangs (h.syndactylus)
produce the most complex duets known in mammals .

E.g., among the gray gibbons (h.muelleri), adult males sing long
songs before sunrise; females sing with males after sunrise and
before 10:00am. Their duets average 15 minutes and occur on a daily
basis. Lone males sing longer songs than paired males, possibly to
attract mates. Unpaired females rarely sing. Different gibbon species
duet for varied lengths of time up to +/- 40 minues.


Does the idea of discourse and gender enter here?

The term 'song' describes the sounds produced by animals which are
for the most part pure in tone and musical in nature, produced
without any overt external stimulus. This contrasts with 'call' which
describes sounds that are short in duration and directly elicited by
specific external stimulus. The 'duet song' is made up of those
sounds categorised as song in which both sexes produce their loud
sounds in an *interactive* manner; turn taking in a mutually
cooperative and coordinated display with *recognisable syntax* [see
Thorpe 1961, Tenaza & Tilson 1977, Whitten 1980, Haimoff 1983, 1984,
1985, &c].

Geissmann's recent studies (1999-2000) apparently confirms Wickler
(1980), i.e. the pair-bonding hypothesis appears to be one of the few
biological functions suggested so far which could explain a high
degree of duet-complexity as adaptive. Territoriality, as well, plays
an integral role. Duets are thought to defend and describe mates
and/or self, and/or space.


Monogamy is found in only 3 per cent of mammals and so is a topic of
debate concerning gibbons. One idea has it that rather than monogamy
being a product of the female needing defense by the male, monogamy
results from other ecological factors, such as food availability and
range size. Another idea on the maintenance of monogamy concerns
females and their range defense songs. It's been suggested that
female response to other songs forces males into monogamy. Another
hypothesis has it that monogamy is a result of the males' inability
to monopolise more than one breeding female - perhaps due to the low
density and even dispersion of females as well as rigorous
requirements for male parental care. Except for [varying degrees of]
direct
maternal care, there is little behavioral variation between the sexes.

The advantage, here, of monogamy is clear: the learning, development
and elaboration of interactive communication requires longterm
reciprocal association. The males of numerous gibbon species share in
the care and raising of their young. Both male and females are known
to teach, that is, to pass on the songs and duets to their offspring
who live in the 'family' unit for +/- nine years and leave in
adolescence to find their own mates.


In 'Current Topics in Primate Vocal Communication' (1996), Lieberman ("What
primate calls can tell us about human evolution") writes: "given the many
similarities that exist between human speech and primate vocalisations [one
can see] human speech evolving in stages; adaptations that at first yielded
neural mechanisms that extended or modulated the relationships that hold
between particular primate vocalisations and particluar emotional states."


All eleven of the gibbons species are considered seriously
endangered. Of course, being strictly territorial, their behaviour is
radically modified in captivity. It may soon be too late to learn
from them.
--


If she doesn't already have it, Geissmann's site will be of use to
your student:

Gibbon Research Lab & portal to gibbon network & other primatology links;
abstracts, articles, contacts, &c. Knowledge of german (as well as
Southeast Asian languages) is helpful.
http://www.tiho-hannover.de/gibbons/main/begruessung.html

Listed at this site under 'News' are the abstracts/contacts from the
recent 'Gibbon Diversity and Conservation' symposium at the 19th
Congress of the International Primatological Society held in Beijing
this past August. There are several abstracts & addresses that might
interest your student, e.g. Susan Lappan, Michael Tomasello, &c.

I hope this is helpful.
Marsha Chuk