Parau, L. G.; Kingma, S. A.; Weigl, S. E.; Dugdale, H. L.; Lessells, C. M.; Schroeder, J.: Dynamics in numbers of group-roosting individuals in relation to pair-sleeping occurrence and onset of egg-laying in European Bee-eaters Merops apiaster. Journal of Ornithology 158 (4), pp. 1119 - 1122 (2017)
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.