Seed dispersal by chimpanzees 67chimpanzees at times have to resort to feeding on terrestrial herbaceous vegetation
(THV) as a fall-back food in the absence of ripe fruits. Additionally (and to us at Sonso
strangely) chimpanzees at Kibale feed on figs as a fall-back food, not as a primary food
(Wranghamet al. 1993; Conklin and Wrangham 1994). This is perhaps because fig trees
at Kibale are less common than at Budongo, possibly because they have not had the
benefit of so much selective logging (Reynolds 1992). As we have seen, in the area of
Budongo where we have been working,F. suris one of the two favourite food species.
If all figs are considered together, then figs become the most preferred food type of all.
Newton-Fisher (1999a) writes, ‘It may be better to regard figs as a staple, rather than
fallback, food.’
Food availability and potential food availability for the Sonso chimpanzees have actu-
ally been measured in three separate studies using three different methods. The work of
Plumptreet al. (1997) has already been referred to. It was based on transect walks and
phenology records over a two-year period. Newton-Fisher’s measures of availability
were based on a 15-month study, during which he recorded the time spent feeding and
foods eaten by the chimpanzees in his study sample (Newton-Fisher 1999a). Reynolds
(unpublished data) studied the number of chimpanzee food trees in a large number of
blocks in the trail system to the north, east and west of Sonso camp, regardless of their
phenological state, and obtained a measure of potential food availability by multiplying
the number of stems of each species by their DBH. All three methods make certain
simplifying assumptions, but all three indicated that this area is rich in food for
chimpanzees (see Chapter 1 for why this might be so).
An interesting area of study on which a start has now been made is the question of
how, in practical terms, chimpanzees find their way from one food source to another.
Subjectively, it has always seemed to observers that they do in fact know where to go
when they finish at one feeding site and head off to another. Sometimes the distance they
travel is great, as much as several kilometers across the forest. How do they know where
to go, and how do they find their way? This topic forms the subject of a current study at
Budongo (Bates, 2005).
Seed dispersal by chimpanzees
From 1991 to 1994 Chris Bakuneeta, studying for his Ph.D. at Makerere University,
washed dung samples collected from the Sonso chimpanzees to determine what seeds
were excreted. These were collected, and where possible identified, and are housed in
the collection in the Herbarium at Sonso camp. Many of these seeds have never been
identified. Chimpanzees tend to swallow a lot of seeds; they are good dispersal agents
because they move quite large distances (often several kilometers a day) thus taking
seeds far from their parent trees. And they deposit a large lump of manure with the seeds
when they defecate, so that the seeds are able to benefit and have an advantage over
those that simply fall to the forest floor beneath the parent tree.
A large number of the seeds dispersed by chimpanzees are from trees that have uses
for the timber industry. Kityo and Plumptre (1997) list the tree species in Uganda that