We studied variations in diet and abundance of the bat Sturnira lilium (Chiroptera: Phyllostomidae) in a montane Atlantic Forest, in order to investigate if patterns in this habitat differ from those in the better-studied lowlands. The diet of S. lilium was assessed based on fecal samples, whereas possible variations in abundance were documented based on capture success. We also monitored and linked variability in air temperature to fruit production of Solanaceae, the main food of S. lilium. Bats fed exclusively on fruits, mostly on Solanaceae and occasionally on Piperaceae and Cecropiaceae. S. lilium was mostly absent in the area during the colder months, suggesting that they might migrate to lower and hence warmer elevations. Absence of the bats was not related to a distinct decline in availability of fruit of Solanaceae because fruit production was not related to temperature. We conclude that in tropical montane systems, abundance of some frugivorous bats might be affected more by air temperature than by food availability. Furthermore, we reinforce the idea that preserving elevational gradients is a crucial aspect for the conservation of migratory species.