Although frogs are predominately opportunistic carnivores, numerous studies report large amounts of plant material in anuran stomachs, citing accidental ingestion as the likely cause. Herein, we present evidence suggesting deliberate plant uptake in the Sabre-toothed Frog (Odontobatrachus ziama) and propose that this trait is specific to the entire family Odontobatrachidae. We performed stomach-flushing on 814 frogs, resulting in 665 dietary samples comprising all 5 Odontobatrachus species and two similar-sized, syntopic frogs, Astylosternus occidentalis and Conraua alleni. We collected dietary samples across the entire range of Odontobatrachus, in both wet and dry season. Additionally, we collected stomach contents of an O. ziama population during a 12-d capture–mark–recapture study in three different river habitats and compared the consumed and available plant material. We found that all Odontobatrachus spp. ingested the pinnate leaf of the riparian tree Parkia bicolor. These leaves were the most abundant food items in the stomachs of three out of the five Odontobatrachus species. Although mean proportional uptake of the leaflets did not differ seasonally, the maximum amount of leaflets was greater during the dry season, coinciding with peak leaflet availability. We found up to 100 single leaflets in stomachs of Odontobatrachus arndti, but syntopic Astylosternus and Conraua had ingested considerably smaller quantities of Parkia leaflets. Lastly, we found a greater prevalence of Parkia leaflets in females, with significant variation in leaflet uptake between stream microhabitats that could not be explained by the availability of the plant material. Consequently, we analyzed the dietary items for co-occurrences of plant material and preyed-upon animals that would support the hypothesis of an accidental uptake. However, we could not find biologically meaningful co-occurrences. Based on the combined results of stomach-flushing, availability of food items, absence of meaningful co-occurrences of plant with animal matter and feeding experiment, we concluded that leaflets were likely swallowed deliberately, but not eaten for energy demands. The reason for the deliberate ingestion of plant material across the genus Odontobatrachus so far remains unresolved.
Key words: Astylosternus occidentalis; Conraua alleni; Frog diet; Guinea; Herbivory; Parkia bicolor; Stomach-flushing