Diet and Food Choice in Peruvian Red Uakaris (Cacajao calvus ucayalii): Selective or Opportunistic Seed Predation?
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Even primates considered dietary specialists tend to eat a combination of fruit pulp, seeds, other plant parts, or animals. Specialist seed predators could either feed on seeds preferentially, or to avoid competition when ripe pulps are scarce. Pitheciin monkeys have specialized dentition that allows them to feed on seeds protected by hard shells, and the upper limit on the hardness of these is likely to be a function of jaw size. We recorded the diet of Peruvian red uakaris (Cacajao calvus ucayalii) on the Yavari River, Peru, to test the prediction that this seed predator would feed on the seeds of hard-shelled fruits preferentially over softer ones in relation to their availability in the forest. We also tested predictions that adult male, adult female, and juvenile diets would differ, with larger individuals eating more hard fruits. Uakaris ate 55.4% seeds, 38.9% pulps and arils, and 5.6% other items, but proportions varied through the year. More pulps, especially from the palm Mauritia flexuosa, were eaten when fruit availability was low, and more hard fruits were positively selected for than softer ones. Juveniles did not open the hardest fruit species opened by adults, and adult males ate harder fruits than females. These results provide evidence that seed eating in some primates has evolved beyond a means of avoiding competition for the ripe pulps typically preferred by many primates. Specialist seeding-eating primates therefore occupy divergent niches that require separate consideration from those of similar-sized primates.
KeywordsCacajao Diet Pitheciin Pitheciini Uacari Uakari
Data collection was funded by Rufford Small Grants, LA Zoo, Conservation International, Primate Conservation Inc. and was supported logistically by the Wildlife Conservation Society and the Earthwatch Institute. We collected data with a permit from INRENA (Instituto Nacional de Recursos Naturales) of the Peruvian government, and the methodology complied with their regulations. Botanists Corine Vriesendorp, Marco Rios, Ricardo Zarate, and Robin Foster identified trees and fruits in the field and from samples and photographs, and Alfonso Mendez and Olivia Curno were indispensable in their help with the fruit transects. We thank WCS and DICE, Pablo Puertas, Miguel Antunez, Pedro Perez, Maribel Recharte, Paddy Brock, the boat crews of Amazoneco, field assistants of WCS, and the people of Carolina and Nuevo Esperanza. We especially thank Gurdun Sperrer and the Pilpintuwasi Amazon Animal Orphanage, Iquitos for their participation in our research. We thank Blake Morton for his comments on a draft of this article, and Jessica Rothman and 2 anonymous referees whose comments greatly improved the manuscript.
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