Seasonal activity is a fundamental driver of ecological interactions. In dam regulated rivers, flow regimes and water temperatures are often asynchronous with natural seasonal patterns. In this study, we tested whether year-round aquatic insect subsidies in a dam-regulated river system mediate seasonal constraints on bat activity, particularly during the winter months. We quantified seasonal bat activity along the Colorado River corridor in Grand Canyon National Park using two years of passive acoustic monitoring across winter and active seasons. We paired species-level activity collected from April 2023 to November 2024 with functional trait data describing bat flight morphology and foraging ecology, as well as temperature and aquatic insect availability. Bat species clustered into three activity classes: species active year-round, species that were consistently rare throughout the sampling period, and species that were strongly seasonally filtered. Seasonal bat activity and prey availability were both highest at warm temperatures. Prey availability was an important predictor of bat activity year-round (p = 0.00171), but was a better predictor in winter (p = 2e-16) than the rest of the year (p = 2.17e-06). Our findings highlight the importance of aquatic insect availability for structuring consumer activity at higher trophic levels, underscoring desert river corridors as essential subsidies for cross-ecosystem energy transfers. Given ongoing pressures facing bat populations, including the impacts of white-nose syndrome, these findings could inform management applications for Glen Canyon Dam operations aimed at supporting bat diversity through winter insect availability.