When rapid changes in environmental factors occur in tropical rain forests, anurans may behaviorally alter their vertical microhabitat in response. Friajes are extreme weather phenomena that bring cold southern winds into Amazonia. Five friaje events during 1997 and 1998 in southern Peru were studied to examine whether anuran populations differed between visual encounter surveys conducted on friaje nights versus non-friaje nights. Anuran diversity, species richness, and number of hylid individuals were significantly greater during friajes in Peru. Friajes alter anuran vertical distributions by causing arboreal frogs to descend to lower levels in order to avoid the cold temperatures and desiccating winds associated with friajes.