Frohlich, M.; Lee, K.; Setia, T. M.; Schuppli, C.; van Schaik, C. P.: The loud scratch: a newly identified gesture of Sumatran orangutan mothers in the wild. Biology Letters 15 (7), 20190209 (2019)
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.