Stable Isotopes Reveal that Little Brown Bats have a Broader Dietary Niche than Northern Long-Eared Bats

Stable isotope analysis (SIA) was used to quantify intra- and inter-specific variation in the delta C-13 and delta N-15 values in plagiopatagium tissue of little brown (Myotis lucifugus) and northern long-eared (M. septentrionalis) bats in several regions of the Canadian Maritimes where they occur in sympatry. There was large intraspecific variation in the delta C-13 of M. lucifugus, with the range exceeding 30 parts per thousand, whereas the range of delta C-13 values observed in M. septentrionalis was less than 7 parts per thousand. Similarly, the standard ellipse area of M. lucifugus was larger than that of M. septentrionalis at all sites and together, these data support the contention that M. lucifugus has broader dietary niche breadth than M. septentrionalis. Some M. lucifugus from Fundy National Park, New Brunswick exhibited very low delta C-13 values, suggesting an energy input from an unknown source, possibly with carbon assimilated from biogenic methane. High delta C-13 values for M. lucifugus from Brier Island, Nova Scotia are consistent with a diet that is at least partially derived from marine sources. Finally, delta N-15 values for both species from Prince Edward Island were high relative to New Brunswick or Nova Scotia, suggesting inputs of anthropogenically-derived nitrogen from a more agriculturally-intensive landscape.