Boubli, J. P.; Eriksson, J.; Wich, S.; Hohmann, G.; Fruth, B.: Mesoscale transect sampling of trees in the Lomako-Yekokora interfluvium Democratic Republic of the Congo. Biodiversity and Conservation 13, pp. 2399 - 2417 (2004)
Scientists studying a rare population of tool-using chimpanzees have found that aging can have a profound impact on their abilities—but not all chimps decline equally.