Decaying Raphia farinifera Palm Trees Provide a Source of Sodium for Wild Chimpanzees in the Budongo Forest, Uganda

Vernon Reynolds,Christopher J English,Andrew W Lloyd,Fred Babweteera,Virginia J Vitzthum

doi:10.1371/journal.pone.0006194

Vernon Reynolds, Christopher J English + Show 3 more

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https://doi.org/10.1371/journal.pone.0006194

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Abstract

For some years, chimpanzees have been observed eating the pith of decaying palm trees of Raphia farinifera in the Budongo Forest, Uganda. The reasons for doing this have until now been unknown. An analysis of the pith for mineral content showed high levels of sodium to be present in the samples. By contrast, lower levels were found in bark of other tree species, and also in leaf and fruit samples eaten by chimpanzees. The differences between the Raphia samples and the non-Raphia samples were highly significant (p<0.001). It is concluded that Raphia provides a rich and possibly essential source of sodium for the Budongo chimpanzees. Comparison of a chewed sample (wadge) of Raphia pith with a sample from the tree showed a clear reduction in sodium content in the chewed sample. Black and white colobus monkeys in Budongo Forest also feed on the pith of Raphia. At present, the survival of Raphia palms in Budongo Forest is threatened by the use of this tree by local tobacco farmers.

Highlights

The chimpanzees (Pan troglodytes schweinfurthii) of the BudongoForest Reserve, Masindi District, Western Uganda, were initially studied by one of us (VR) in 1962 [1], and have been studied continuously since 1990 [2]
The study community of chimpanzees is named the Sonso community after the River Sonso which runs through its range
1990, individuals and small parties of the animals have been seen occasionally eating the pith of dead Raphia trees, but until now the reason for doing so has not been known

Summary

Introduction

At various places along the river, Swamp Forest prevails. Swamp Forest contains several Raphia farinifera palm trees. The bole rots down until it consists of a hard outer bark with a soft, moist, fibrous woody pith. Chimpanzees make a small hole in bark at the base of the dead tree with their teeth, widen it with their fingers and later their hands. Through the hole, they extract dead pith, chew it thoroughly, swallow the juice and some particles of woody matter, and spit out a fibrous wadge of chewed pith. The reason for consumption of the dead Raphia pith has not been known

Discussion

Results

Materials and Methods