Adaptation by Budongo Forest chimpanzees (Pan troglodytes schweinfurthii) to loss of a primary source of dietary sodium

Chimpanzees of the Sonso community living in the Budongo Forest Reserve in western Uganda have in the past obtained sodium from the pith of decaying Raphia farinifera (RF) palm trees, which occur in areas of Swamp Forest. In recent years there has been a decline in numbers of trees of this species, mainly owing to the demand for leaf stems for the production of Raphia string, used by local tobacco farmers to tie tobacco leaves during drying and curing. Faced with a declining number of dead Raphia trees, the chimpanzees of the Sonso community have increased their feeding on a different tree species, Cleistopholis patens (CP), which also occurs in Swamp Forest. We analysed samples of dead wood from CP and found it to contain higher concentrations of sodium than other plant species tested, but lower concentrations than found in RF. CP has now become the main vegetative provider of sodium for the Sonso chimpanzees. Discussions are currently taking place with British American Tobacco (BAT) and local tobacco farmers in an effort to get them to switch from Raphia string to cotton string.