Hydrogen stable isotope ratios of keratin (δ2HK) are increasingly used as endogenous markers to study animal movements, yet it is unclear what factors might influence δ2HK in free-ranging animals. We studied hydrogen stable isotope ratios of body water (δ2HBW) and fur keratin in 36 bat species (>400 individuals) from a tropical forest assemblage to evaluate if δ2HBW and δ2HK are related to body size, trophic position, and movement ecology. We found a relatively large range of δ2HBW values (∼65‰) across bat species. Our phylogenetically controlled analysis showed that δ2HBW was not related to body size, trophic position, or movement ecology of species. The analysis also indicated that δ2HBW of primary consumers (i.e., fruit-eating bats) was similar to that of fruit juice, and δ2HBW of secondary consumers (i.e., animalivorous bats) was similar to that of surface water. Across bat species, δ2HK tended to decrease with increasing δ2HBW, suggesting that δ2HK is not directly linked to δ2HBW. We further tested whether δ2HK varied with a species' trophic position (measured as δ15N) and movement ecology (local or regional species). In syntopic bats, δ2HK ranged over 73‰, yet δ2HK was related neither to δ15N nor to the movement ecology of species. Fur keratin of secondary consumers was more enriched in 2H by 44‰ and in 15N by 3.7‰ compared with fur keratin of primary consumers. In an intraspecific analysis, we found that δ2HK of an insectivorous bat varied by 20‰ between colonies at 4 km distance. Within this species, δ2HK was not related to individual δ15N and body mass. Our data suggest that variation in δ2HK can be large in bats of tropical assemblages, both across species (range ∼70‰) and even within sedentary species (range ∼20‰), and that δ2HK is largely affected by the dietary habits of species.