There is widespread evidence that feeding ecology can lead to differences in mammalian social systems. To understand how diet and ecology affect the social behavior of ring-tailed coatis (Nasua nasua), detailed measures of feeding behavior were recorded from 2 well-studied groups over a 2-year period. The proportion of fruit and invertebrates in the diet of ring-tailed coatis in Iguazu, Argentina, was very similar to that in diets of white-nosed coatis (N. narica) and ring-tailed coatis studied at field sites in Brazil. Consumption of vertebrates in Iguazu was exceptionally rare. The proportion of time spent foraging for invertebrates and fruit generally matched seasonal changes in the abundance these foods in the environment. During the winter, when invertebrate and fruit availability was low, coatis spent a large amount of time feeding on 2 exotic fruit species. The presence of exotic fruits provided coatis with food during the lean winter season and may have influenced the high reproduction and survivorship found in this population. Coatis spent about 44% of their fruit-foraging time exploiting pindo palm (Syagrus romanzoffianum) fruits and it appeared that this fruit species played a major role in shaping the ranging and feeding behavior of coati groups. The time spent foraging at fruit trees and the total number of fruits eaten varied depending on the species of tree. Coati groups spent an average of 2.5–12.5 min feeding on different species of fruit trees, and coati groups ate an average of 2.6–269.8 fruits per tree species. The quick depletion of fruit trees and high density of foraging individuals, especially when feeding on pindo, plays an important role in shaping the social system of coatis.