“…When chimpanzees face fruit scarcity, they tend to eat lower-quality foods (or fallback foods, which are more difficult to digest) consisting of leaves, seeds, blossoms, stems, bark and resin [e.g., Conklin-Brittain et al, 1998;Wrangham et al, 1998;Constantino et al, 2009;Wood and Schroer, 2012]. In particular, the diet of eastern chimpanzees ( Pan troglodytes schweinfurthii ), the sample analyzed in this study, is characterized by strong seasonal changes, with a shift to more fibrous foods, such as leaves, pith and bark, during periods of low fruit availability [Nishida et al, 1983;Wrangham et al, 1998;Emery-Thompson and Wrangham, 2008;Chancellor et al, 2012;Watts et al, 2012]. Comparatively, orangutans are also identified as primarily frugivorous but rely heavily on tough and highly fibrous fallback foods [Mackinnon, 1974[Mackinnon, , 1979Taylor, 1998Taylor, , 2002Taylor, , 2006Delgado and Van Schaik, 2000;Wich et al, 2009;Kanomori et al, 2010;Terhune, 2013].…”