Chimpanzees of the Budongo Forest : Ecology, Behaviour, and Conservation

away from the body and putting them into the mouth. Stokes and Byrne show in great
detail how the process of feeding on leaves can be broken down hierarchically into
several dozen component parts. The fact that all chimpanzees feed in the same two basic
ways indicates a high degree of learned technique. With this degree of detail to explore,
they were able to show that injured chimpanzees, while showing the same techniques
as able-bodied individuals, modified them according to the details of their specific
impairments.
For example, to pull Broussonetialeaves into range, different injured individuals used
novel techniques such as knuckle hook, wrist wrap, back of wrist reach, lateral wrist
reach, and wrist grasp reach. Because of loss of hand function, having reached and
pulled in a branch for feeding, they supported the branch using the back of the wrist,
hooked wrist, lateral wrist, wrist-wrap, knuckle hook, wrist grasp and a variety of

176 The problem of snares

High

Intermediate

Low

• 0.8
  N = 15
  Uninjured

10

Injured

–0.6

• 0.4

–0.2

0.0

Mean relative height

0.2

0.4

0.6

(b) 0.8

(a)

Fig. 9.6: (a) Schematic Ficus surtree showing classification of feeding positions. (b) Boxplot
showing difference in relative feeding height of injured and uninjured chimpanzees on F. surtrees.
They-axis shows the mean feeding position of uninjured (left) and injured (right) individuals relative
to zero. Zero represents the mean for all individuals (from Smith 1995).