THOSE VAIN AERIAL WAYS: DETERMINING THE RELATIVE IMPORTANCE OF AQUATIC INSECTS IN THE DIETS OF BATS USING STABLE ISOTOPES, SCAT ANALYSIS, AND RADIO-TELEMETRY.

R.R. Doucett¹, H.G. Broders², G. Quinn², and G.J. Forbes². ¹Colorado Plateau Stable Isotope Laboratory, Department of Biological Sciences, Northern Arizona University, PO Box 5640, Flagstaff, AZ, 86011, ²New Brunswick Cooperative Fish and Wildlife Research Unit, Department of Biology, University of New Brunswick, PO Box 45111, Fredericton, NB, E3B 6E1

Stable-isotope ratios (δ¹³C and δ¹⁵N), scat analysis, and radio-telemetry were used to determine the importance of terrestrial and aquatic insects to the diets of two sympatric bat species (Myotis septentrionalis and M. lucifugus) in Fundy National Park, New Brunswick, Canada, during the summer of 2000-01. Although scat analysis could not identify differences in diet between the two species, telemetry data indicated that M. lucifugus foraged near water, while M. septentrionalis spent more time in the forest. Overall, δ¹⁵N values of both species were similar (2 to 8 per mil), however δ¹³C values of M. lucifugus (-55 to -20 per mil) were more variable than those of M. septentrionalis (-30 to -26 per mil). Large variation in δ¹³C values for M. lucifugus was not consistent with a terrestrial diet, suggesting that this species foraged almost entirely on aquatic insects. Extremely negative δ¹³C values values (-55 per mil) in M. lucifugus may have resulted from methane-incorporation into aquatic food webs (peat bogs), and through insect emergence, were passed on to aerial predators. Results suggest that stable isotopes are not only useful for delineating between terrestrial and aquatic insects in animal diets, but also for distinguishing between individuals foraging over different aquatic habitats.