Poot, H.; Ter Maat, A.; Trost, L.; Schwabl, I.; Jansen, R. F.; Gahr, M.: Behavioural and physiological effects of population density on domesticated Zebra Finches (Taeniopygia guttata) held in aviaries. Physiology & Behavior 105 (3), pp. 821 - 828 (2012)
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.