Potential and limits in detecting altitudinal movements of bats using stable hydrogen isotope ratios of fur keratin

Despite their small size, bats are exceptionally mobile. But where and when bats move seasonally often remains enigmatic, particularly for altitudinal movements. Recently, stable hydrogen isotope ratios (δD) of metabolically inert material like hair keratin have been utilized to track altitudinal movements of animals. Here, we measured δD in hair keratin of seven bat species captured in the Merendon Mountain Range in Honduras: three species were captured only at the low elevation site (≈ 1,100 m above sea level), one species only at the high elevation site (≈ 1,500 m a.s.l.) and three species at both sites. Based on information from the literature, we categorized two out of the seven species as sedentary (obligate fruit-eating Artibeus toltecus and insect-feeding Micronycteris microtis). All others were categorized as potentially migratory species (obligate fruit-eating Artibeus jamaicensis, Sturnira ludovici and Sturnira lilium and insect-feeding Myotis keaysi and Molossus ater). Hair keratin of insectivorous species was enriched in deuterium by about 40‰ relative to that of co-existing fruit-eating species, irrespective of whether they were sedentary or potentially migratory, suggesting that δD of consumer tissue increases markedly with increasing trophic level. Hair keratin of sedentary A. toltecus and potentially migratory S. ludovici did not differ between populations of the two elevations indicating that the altitudinal gradient in δD may be too small and/or that variation in hair keratin δD too large to unravel altitudinal movements of less than 400 m in bats based on keratin δD alone.