Large numbers of migratory bats are killed every autumn at wind energy facilities in North America. While this may be troubling from a population perspective, these fatalities provide an opportunity to learn more about bat migration and the origins and summer distributions of migratory bats by using endogenous markers. Such markers include stable isotope values, which have been used to answer questions about ecological systems, such as trophic levels and food webs, and the origins and migratory routes of animals. To estimate the origins of migratory bats, we determined nitrogen (δ15N), carbon (δ13C), and hydrogen (δ2H) stable isotope values of fur (δ15Nf, δ13Cf, δ2Hf, respectively) from hoary bats (Lasiurus cinereus) and silver-haired bats (Lasionycteris noctivagans) killed at a wind energy facility in southern Alberta, Canada. We determined that mean isotope values varied among species, year, sex, and age class. δ13Cf and δ2Hf values indicated that silver-haired bats likely originated in the boreal forest, farther north and/or at higher elevations than the aspen parkland-like habitat suggested by the isotope values of hoary bats. IsoMAP analysis indicated that bat fatalities may have originated from a large catchment area potentially hundreds of kilometers away. Our data provide further evidence for a migration route along the eastern slopes of the Rocky Mountains that is used by bats from across Alberta and beyond, and suggest that fatalities at a single wind energy site have the potential to have far-reaching ecological and population consequences.