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Chapter 3
Locomotion
© 1981 Markus Kappeler
Extensive descriptions of locomotion exist for the
white-handed gibbon (N.l.lar/carpenteri/entelloides; s. CARPENTER
[1940,1976], ELLEFSON [1967], BALDWIN & TELEKI [1976]; aspects
of the functional anatomy and evolution of gibbon locomotion
have been treated by ANDREWS & GROVES [1976], LORENZ [1971]
and TUTTLE [1969,1972]).
The statements of these authors are also valid for
H.l.moloch, and will therefore not be repeated here. Rather,
the conditions determining the occurrence of the various locomotion
in the silvery gibbon will be examined.
Locomotion patterns constitute «tool behaviour»
(«Werkzeug-Verhalten», LORENZ [1965]) and are applied
in most functional situations in an ancillary role. While they
are rich in variation, certain main types or techniques can be
recognized. The type or technique actually used depends upon
(1) the functional context, resp. the immediate behavioural goal,
and (2) the substrate comprising the chosen route resp. the temporary
site of the animal.
In the following, the correlations between locomotion
pattern on the one hand, and functional context and substrate
on the other hand will be examined. It is convenient to divide
this discussion into two sections (A) fast locomotion, and (B)
slow.
3.1. Fast locomotion
Characteristic of fast locomotion in the silvery gibbon
are sequences of «flying phases» from branch to branch
and, possibly, from tree to tree. Contact with the substrate
serves to break the fall of the body, and to submit to it the
impulse for a new flying phase towards a new arboreal support.
Basically this is brought about by leaping and brachiation.
When leaping, the actual take-off - from a transitory bipedal
position or reinforced through bipedal running - supplies the
energy for a flying phase; when brachiating, the energy of the
flying body is transferred into a pendulum-like swing - below
the substrate - with the help of one arm at the time, and this
swing leads over into the next flying phase.
Undoubtedly, brachiation with flying phases is the
swiftest form of locomotion in the gibbon. However, it requires
a relatively wide-meshed branching pattern and more or less horizontally
growing branches of medium diameter, as well as a direction of
motion which is approximately transverse to the main growing
direction of the branches.
These substrate conditions are usually fulfilled only
at the middle forest level, which explains why the gibbon as
a rule moves to this level for fast locomotion. Should the conditions
there also impede the continuity of brachiation, phases of bipedal
leaping resp. running and leaping are interposed.
This dependence on the substrate for efficient locomotion
corresponds to the fact that gibbon groups, in every part of
their home range, use a fixed escape route when disturbed and
therefore flee in single file. This permits rapid progress with
well coordinated technical performance and excludes the risk
of erring into a «pathless» situation.
Fast locomotion occurs in various functional contexts,
e.g. predator avoidance (chapter 5), female song bouts (chapter
6), territorial disputes (chapter 7), play behaviour of juveniles.
Corresponding to the percentage of time of the total
activity time spent by the silvery gibbon on these functions,
fast locomotion accounts for a rather small share of the total
locomotion.
3.2. Slow locomotion
In by far most cases, movement from one place to another
is made by slow locomotion. In this way, usually only very short
stretches are travelled at a time; occasionally, however, more
or less constant slow locomotion over 50-100 meters occurs.
In slow locomotion, the sequences of flying phases
are absent. 1-4 limbs are constantly in contact with the substrate.
By temporarily supporting and/or anchoring the body, the limbs
prevent it from falling. One hand or one foot alternately relinguishes
and establishes contact in the direction of motion.
According to how the limbs are used, the following
patterns of slow locomotion may be differenciated:
1. brachiation without flying phases,
2. bipedal walking,
3. brachiation resp. walking with additional temporary use of
the legs resp. the arms,
4. quadrupedal climbing.
The scope of slow locomotion, however, occasionally
also includes
5. flying phases; they serve to traverse gaps between branches
or tree crowns. The impulse is generated by bipedal take-off
or a brachiatory, pendulum-like swing; at the next support, the
falling body can be caught up by the legs or arms, or both legs
and arms together.
Such flying phases are regularly preceded
by a check-up of the situation. In this way, not only is the
locomotory effort planned; but probably also the motivational
component (e.g. the access to resources), which urges the jump,
is computed with the expenditure of energy needed for the jump.
Moreover, a decision may also be made - within the framework
of predator avoidance - between the tendency to move in a conspicuous
manner and the tendency to behave cryptically.
The range of slow locomotion patterns gives the gibbon
the possibility to use all structures of the tree - from tree
trunks of considerable diameter (>1 meter) down to the finest
branches (terminal twigs) - and, consequently, all niches of
the forest, from the ground up to the top of the canopy. Slow
locomotion is therefore not confined to a certain forest level.
In undisturbed situations the members of a gibbon
group move in a swarm and rarely follow fixed routes; travelling
in single file along a familiar and repeatedly used path only
occurs when defiles are present in the home range (e.g. gaps
in the substrate which have to be jumped over, or trunks of free-standing
trees which have to be climbed).
Slow locomotion occurs mainly in undisturbed situations
and serves, summarily, within the framework of survival, to enable
the individual to visit resources and functional places associated
with self-preservation.
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