Primates along with many other animal taxa are forced to cope with large shifts in basic ecological conditions because of rapid anthropogenically induced changes of their habitats. One of the coping strategies for primates is to adjust their diet to these changes, and several studies have demonstrated the importance of fallback resources for this. Bonobos, like chimpanzees, might be particularly vulnerable to habitat fragmentation because of their high dependence on fruit availability. Little is known, however, about bonobo feeding ecology in fragmented habitats and their use of fallback resources. In this study, we investigate diet seasonal variation and the exploitation of preferred and fallback foods in a bonobo population living in forest-savannah mosaics. Results show that bonobos have adapted to this fragmented habitat by feeding on only a few fruit species, including an important number of non-tree species (liana, herb and savannah shrub), in comparison to populations living in dense forests. These non-tree plants have been defined as fallback and non-preferred foods, which are most probably consumed to maintain high frugivory. Interestingly, we identified that preferred foods are all typical of mature forests while fallback resources are mainly found in forest edges or disturbed areas. This finding indicates that bonobos prefer to use mature forests when feeding, as they do for nesting, but extend their range use to forest areas in close proximity to humans when the availability of preferred fruits is low. Finally, we show that bonobo diet relies heavily on two abundant fallback fruits: Musanga cecropioides and Marantochloa leucantha. Other studies have demonstrated that the selection of abundant fallback resources enables primates to subsist at high densities and to maintain cohesive groups, as observed at this study site. Our findings suggest that bonobos living in forest-savannah mosaics can be considered as staple fallback food consumers. Am. J. Primatol. 77:948-962, 2015. © 2015 Wiley Periodicals, Inc.