Using stable isotope analysis to study altitudinal and latitudinal bat migration

The general lack of knowledge on basic aspects of the biology of temperate and tropical bats, their low reproductive rates, and threats such as white-nose syndrome, wind farms, and habitat loss, make them very susceptible to population declines. My research uses an innovative technique, the analysis of stable isotopes, to study the ecology of bat migration with the main goals of contributing significantly to the understanding of bat biology and assessing the conservation status and susceptibility of bats. In the first chapter, I measured the content of hydrogen isotopes in fur samples of migratory bat species killed at a wind farm in northern Indiana to determine their geographic origin. North American tree bats (Lasiurus borealis, L. cinereus, and Lasionycteris noctivagans) are considered long distance migrants. In North America, peaks in bat mortality at wind farms occur between mid-July and mid-September. This period is associated with fall migration of bats from their summer (breeding) grounds to their wintering grounds. Thus, wind turbines may have serious negative effects on a strategic event in the life of bats by interrupting migratory connectivity and thereby imperiling the long-term persistence of migratory bat species at large scales. The analysis accurately predicted the known origin of control samples and estimated that non-control bats killed at the wind farm originated from several populations in the United States as well as in Canada. My results highlighted the threat of wind farms to local bat populations as well as to bats originating far from those farms, and emphasized the need for conservation policies across borders. High variation in stable hydrogen isotopes in migrant individuals of all 3 species was observed, suggesting that individuals or populations from a variety of regions pass through the wind farm. In the second chapter, I evaluated the triple-isotopic (hydrogen, carbon, and nitrogen) composition of the tissues of 7 bat species collected at 3 altitudes in the Central Andes of Peru, and the variation of these isotopes across an altitudinal gradient, the application of isotope analysis to migration studies, and trophic effect. Previous studies had demonstrated that hydrogen isotopes were a reliable tool to track altitudinal movements of birds, and there was evidence from soil and plant studies that nitrogen and carbon isotopes could serve the same purpose. However, studies focused on bats were lacking. Hydrogen and nitrogen isotopes in the sanguinivorous control were found to be enriched relative to those of the syntopic frugivores. Carbon isotopes in the sanguinivorous bat were depleted when compared to frugivores. Differences in hydrogen found between trophic groups are the first reported for the species studied and support results found elsewhere in the Neotropics. My results demonstrated that, in spite of the wide array of physiological and environmental factors producing temporal and spatial variation, the analysis of hydrogen isotopes is a promising tool to study altitudinal movements of bats when used over long distances. Neither stable isotopes of nitrogen or carbon appear to be reliable to track movements along short gradients such as those along mountains. The contrast of these findings with the results of previous studies suggests that isotopic gradients may be specific to given taxon and localities. My results contributed to the understanding of bat movement patterns and therefore to assessing their sensitivity to potential threats such as habitat loss and connectivity.