Pennycuick, C. J.; Fast, P. L. F.; Ballerstaedt, N.; Rattenborg, N. C.: The effect of an external transmitter on the drag coefficient of a bird's body, and hence on migration range, and energy reserves after migration. Journal of Ornithology 153 (3), pp. 633 - 644 (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.