Although big brown bats (Eptesicus fuscus) occur throughout North America and are considered to be well adapted to urban environments, this species has been declining for over two decades in Southern California. Various studies indicate that big brown bats are scarce in areas more than a few kilometers from large contiguous undeveloped areas and suggest that this species is highly intolerant of habitat fragmentation. While the protection of roosts is often the focus of bat conservation efforts, protection of foraging habitat and prey base are often overlooked despite their importance. We hypothesized that big brown bats may have limited dietary flexibility in this region relative to other parts of their range, and that those roosting at the urban-wildland interface in Southern California consume insect prey that are associated with native vegetation and that are not abundant in urban environments. We collected guano samples from maternity roosts at the urban-wildland interface in Southern California and used DNA metabarcoding to analyze insect prey consumed by these colonies. We will present the first known description of diet for this species in a Mediterranean ecosystem, and also discuss the landscape associations of their prey in context with conservation recommendations for this declining species.