The coexistence of multiple species of short-tailed fruit bats (Phyllostomidae: Carollia) is common throughout the range of the genus. Previous studies of fecal and stomach contents have documented differences in dietary breadth and in habitat use as mechanisms by which these species may partition dietary niches. By comparing values of δ¹⁵N and δ¹³C across species of Carollia from 17 sites in Central and South America, we show that co-occurring Carollia frequently differ in dietary breadth, foraging habitats, and level of insectivory. Values of δ¹⁵N, which tended to be enriched in C. castanea, depleted in C. perspicillata, and intermediate in C. brevicauda and C. sowelli, indicate trophic stratification. Values of δ¹³C followed the opposite trend, tending to be enriched in C. perspicillata and depleted in C. castanea, suggesting interspecific differences in breadth of the foraging area. Isotopic comparisons among Carollia, other bat species, and potential food items at 5 of our sites illustrate that populations of Carollia tend to be trophically intermediate between strictly phytophagous and strictly insectivorous organisms, and, contrary to the paucity of insect remains found in fecal samples, indicate that the consumption of insects by Carollia is more common and potentially more important than previously was thought.