AbstractHere we assessed the efficacy of performing field surveys during both dry and rainy seasons to estimate species richness and composition of phyllostomid bats in 12 sites of the Brazilian Atlantic Forest. Our goal was to elucidate two opposite scenarios. If bat species compositions differ between the dry and rainy seasons, then field surveys in both seasons will be considered complementary for estimating local bat assemblages. In contrast, if bat species compositions in the dry season are a nested subset of the species present in the rainy season, then field surveys in both seasons will be considered redundant. Our results showed that field surveys performed only during the rainy season exhibited the same efficacy in recording bat species as field surveys considering both dry and rainy seasons combined. Consequently, the rare species sampled in the rainy season contributed to the uniqueness of communities in terms of species composition. Considering that time, funding, and the number of field personnel available for work are important factors when determining the sampling effort in highly biodiverse regions like the tropics, our results can be useful in establishing protocols for research projects with limited resources aiming to create a comprehensive list of species.