Summary: Many North American bat species are highly mobile and exhibit substantial intraspecific variability in migratory movements. Documenting this variability, and the correlates of different migratory strategies, can deepen our understanding of the evolutionary drivers of migration and the factors shaping individual decisions about whether and how to migrate. Progress in understanding bat migratory ecology has been slowed by the difficulties inherent in observing and tracking these cryptic animals. Consequently, research efforts must address fundamental questions about movement-tracking methodologies and basic migratory patterns, alongside broader questions relating to migratory ecology. I will discuss work by my research group and collaborators that addresses these topics, with particular emphasis on our use of stable hydrogen isotope techniques to elucidate the migratory movements of North American bats. Our work focuses especially on species exhibiting partial and differential migration, as well as on phenotypic differences among individuals with different migratory histories.