Kalbitzer, U.; Heistermann, M.: Long-term storage effects in steroid metabolite extracts from baboon (Papio sp.) faeces a comparison of three commonly applied storage methods. Methods in Ecology and Evolution 4 (5), pp. 493 - 500 (2013)
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.