Covert Carnivory? A Seed-Predating Primate, the Golden-Backed Uacari, Shows Preferences for Insect-Infested Fruits

Insect ingestion is generally recorded when consumption of free-living mobile prey is observed. However, an infrequently-investigated alternative exists: ingestion of insects living within fruits and/or their seeds. Potentially this offers frugivorous vertebrates a substantial source of animal protein, vitamins and micronutrients. Here we report on selection by the golden-backed uacari, Cacajao ouakary, of fruits for their insect content. A Neotropical primate specialized for eating unripeseeds of hard-husked fruits, C. ouakary ate seeds/fruit pulp of 101 plant species, of which 26 showed insect infestation. Comparison of frequencies of infestation in fruits/seeds in diet-fruit remnants with those for on-tree same-aged con specific fruits, showed uacaris were: selecting infested fruits (11 species), eating at uniform frequency (9 species), or actively avoiding (6 species). Infested fruit/seed selection was not based on mechanical advantage from fruit weakened by insect burrows, since C. ouakary preferentially bite pericarp sutures, into which larvae do not burrow. By number of feeding records, the 11 actively-selected plant species contributed >25% of uacaris diet, and the 26 larvae-infested species 41.3%; at least 10.7% of individual fruit uacaris ateare estimated to have been insect-infested. Larval content varied from 0.4-5.5g per fruit, so this form of insectivory may make a significant contribution to C. ouakary diet. As larvae are commonly 60-80% protein, infested-fruit selection may be an important means for primates to access protein not otherwise easily available from fruits/seeds. We consider this topic important for understanding primate foraging decisions, and suggest diet-sampling methodologies should consider this foraging mode. Methods for detecting seed predation could be employed, both within and outside primatology, to recalibrate the contribution of fruit-inhabiting insectsto diets of species considered predominantly frugivorous.

Keywords: Cacajao, insectivory, preferential infestation selection, primate, seed-predation.