Deadwood as a source of sodium for gorillas
In Uganda's Bwindi National Park, the resident mountain gorillas (Gorilla beringei beringei) eat dead and decaying wood from certain plant species to meet their need for the vital nutrient sodium.
This is the first time there is an explanation for this unusual food intake, because dead wood contains hardly any usable nutrients such as sugar or proteins, but instead high amounts of lignin, which primates cannot digest. Nevertheless, the zoologists around Jessica Rothman from Cornell University observed the gorillas - and other monkey species - regularly eating the wood.
A comparative chemical analysis of the preferred wood food with despised wood and other food plants then showed the high content of easily soluble sodium compounds in the selected tree remains. Based on their data, the researchers estimate that the animals could cover up to 95 percent of their sodium requirement in this way, although it does not even make up four percent of their total food intake.
The feeding behavior of the gorillas also speaks in favor of the dietary supplement thesis, because the monkeys chew on the pieces of wood for minutes at times, but ultimately spit them out again and do not swallow them. In this way, the minerals are released from the material with the saliva. Rothman and her colleagues also observed that the gorillas licked tree stumps or rotting trunks to meet their sodium needs.
Since many tropical soils are depleted of minerals due to their old age and the high rainfall, the animal species that are essentially dependent on them - sodium deficiency, for example, is associated with weak bones and growth deficits, among other things - sometimes have to undertake longer hikes to get the to be able to absorb adequate amounts for them. In the African Congo Basin, for example, there are always large gatherings of elephants, antelopes and various monkeys at so-called clay licks to feed on saline soil.