56 Diet and culture at Sonso
of their daily observations.^18 From the start of the BFP in 1990, we have collected samples
of food species and many of these were photographed fresh for our Plant Identification
Album, and subsequently dried and mounted by Andy Plumptre. In cases where the
identification was uncertain they were identified at Makerere University’s Herbarium,
by Perpetua Ipulet, Tony Katende and others, after which they were placed in the BFP’s
Herbarium at Sonso.^19
In 1997, Rhiannon Meredith and Susie Whiten made a list of 76 species of plants that
provided food for the chimpanzees, based on records collected by our field assistants
and researchers. An updated version of this list is included in Appendix B and shows the
months they had been seen eating these species as well as the types of plants and parts
eaten. It can be seen that whereas some species are rarely eaten, others are eaten in every
month of the year. These records are based on observational data and do not imply any-
thing about seasonality of the plant species or that chimpanzees do not eat certain
species in months with blanks on the table; they were simply not observed eating them
in those months.
Chimpanzees were seen to eat parts of the following kinds of plants: trees, shrubs and
herbs, climbers and epiphytes. They fed on the following plant parts: fruits, leaves, flow-
ers, bark, seeds, stem/pith, gum and wood. Of these, ripe fruits and young leaves make
up the bulk of the diet. For very many species, including figs (e.g. Tweheyo and Obua
2001; Tweheyo and Lye 2003) chimpanzees eat the young leaves which are sugar- and
protein-rich. Bark and gum are eaten from Khaya anthotheca, the so-called ‘Budongo
mahogany’; bark is also taken from other species including Ficus exasperata and
Cynometra alexandri. In both the latter cases the inner, sap-covered surface of the newly
stripped bark is licked, while in the case of Khaya, flakes of bark are removed and the
inner surface is scraped off with the incisor teeth. This happens at irregular intervals,
and when it happens many chimpanzees do it. The bark contains high levels of con-
densed tannins (Reynolds et al. 1998); why the chimpanzees occasionally binge on it
remains unknown. There can be long periods when chimpanzees do not eat it at all; from
the late 1990s until the time of writing this book for example, a period of 5 years, no
Khayabark-eating has been seen.
Insects and honey
Infrequently, in addition to the plant foods mentioned above, the diet is supplemented by
animal foods. The Sonso chimpanzees, like the chimpanzees of Kibale, Mahale, Taï and
Gombe, occasionally kill monkeys and eat them. Meat-eating will be dealt with later
in this chapter. They also eat fig wasps in the course of eating figs, and occasionally,
caterpillars. This happened for example in April 1997 when there was an explosion of
caterpillars in the forest and the Sonso chimpanzees fed on them avidly. While I was
(^18) For a list of food species of the Sonso chimpanzees see Appendix B.
(^19) In 2001 the Herbarium, which had been in constant use by students, was checked and where necessary
reorganized by Wilma van Riel. It is currently in good condition but requires the attentions of a botanist to
progress further. Details of the Herbarium are available on the BFP’s website, http://www.budongo.org.