The more elusive forest elephant has not been studied as extensively as the savanna species but some striking differences in social organisation and behaviour are already apparent. These elephants occur in small groups of around 5 - 8 individuals (8), which sometimes come together to form larger 'bond groups' (9). Congregations also occur in swampy forest clearings known as 'bais' (9), where forest elephants usually go looking for minerals (10). Nevertheless, neither of these are anywhere near the size of herds recorded on the African plains (9). Like savanna elephants, however, sound is an important method of communication and forest elephants use low frequency infrasound rumblings that are below the range of human hearing (11). Elephants feed by plucking at grasses and leaves with their trunks, and the diet of the forest elephant is dependent on season (9). During the dry season, they mainly browse on grasses and leaves but in the wet, fruit is preferentially eaten (9). These elephants have a number of highly specialised relationships with forest plant species and there are a number of hard-shelled fruits such as those of the Makore tree that can only be opened and broken down by elephants (8); some fruits are broken by the dextrous use of tusks to pierce the hard outer coat.