Partitioning of foraging niches of insectivorous bats likely is shaped by ecological factors such as availability of prey and competition; however, these factors are difficult to measure and there is little empirical evidence for either. We examined diet of the North American big brown bats (Eptesicus fuscus) and little brown bats (Myotis lucifugus) using published works and our own data from New England to better understand intraspecific dietary variation, and to test whether diet corresponded with climate (an indicator of availability of prey) and species richness of bat communities (a measure of potential interspecific competition). Diet of both species of bat varied with climate in a manner that generally corresponded with longitude. E. fuscus increased use of moths in regions with cool arid summers (western North America), whereas both species of bat consumed more beetles in moister summer climates associated with eastern North America. Additionally, E. fuscus consumed fewer beetles and more moths and true flies in more diverse bat communities. However, correlation between richness of bat communities and mean monthly precipitation limits interpretation of whether richness of bat communities influenced foraging beyond effects of climate alone. Results suggest diet is influenced indirectly by environmental factors that limit availability of prey. Further examination of these and other factors related to intraspecific dietary variation in insectivorous bats is warranted and likely to yield valuable ecological insight.