Ecological and dietary correlates of stable hydrogen isotope ratios in fur and body water of syntopic tropical bats

Hydrogen stable isotope ratios of keratin (delta2H(K)) are increasingly used as endogenous markers to study animal movements, yet it is unclear what factors might influence delta2H(K) in free-ranging animals. We studied hydrogen stable isotope ratios of body water (delta2H(BW)) and fur keratin in 36 bat species (> 400 individuals) from a tropical forest assemblage to evaluate if delta2H(BW) and delta2H(K) are related to body size, trophic position, and movement ecology. We found a relatively large range of delta2H(BW) values (approximately 65 per thousand) across bat species. Our phylogenetically controlled analysis showed that delta2H(BW) was not related to body size, trophic position, or movement ecology of species. The analysis also indicated that delta2H(BW) of primary consumers (i.e., fruit-eating bats) was similar to that of fruit juice, and delta2H(BW) of secondary consumers (i.e., animalivorous bats) was similar to that of surface water. Across bat species, delta2H(K) tended to decrease with increasing delta2H(BW), suggesting that delta2H(K) is not directly linked to delta2H(BW). We further tested whether delta2H(K) varied with a species' trophic position (measured as delta15N) and movement ecology (local or regional species). In syntopic bats, delta2H(K) ranged over 73 per thousand, yet delta2H(K) was related neither to delta15N nor to the movement ecology of species. Fur keratin of secondary consumers was more enriched in 2H by 44 per thousand and in 15N by 3.7 per thousand compared with fur keratin of primary consumers. In an intraspecific analysis, we found that delta2H(K) of an insectivorous bat varied by 20 per thousand between colonies at 4 km distance. Within this species, deltaH(K) was not related to individual delta15N and body mass. Our data suggest that variation in delta2H(K) can be large in bats of tropical assemblages, both across species (range approximately 70 per thousand) and even within sedentary species (range approximately 20 per thousand), and that delta2H(K) is largely affected by the dietary habits of species.