Seasonality over lunar phases drives flight activity of co-roosting bats, Rhinolophus rouxii and Rousettus...

Nocturnal activity in bats is defined by the timing of flight initiation at dusk and flight termination at dawn. In addition to the endogenous 24-hour circadian rhythm, these flight activities are influenced by environmental cues operating over longer timescales, particularly lunar phases and seasonal variation. Although the influence of lunar phases on the flight activity of Rousettus leschenaultii has been reported, little is known about their effects on Rhinolophus rouxii or about how seasonal variation influences the emergence and return times of these two co-roosting bat species over an annual cycle. The abandoned temple-like structure, Gaddige Maṭha, located between forests and village settlements in Western Ghats, provides a unique opportunity to compare the flight activities of two species with contrasting foraging guilds in a shared roosting environment. We investigated the effects of 12 consecutive lunar cycles (comprising four lunar phases) and three seasons (winter, summer, and monsoon) on bat emergence and return flight timings. Emergence and return surveys were conducted from October 2024-September 2025, and the data analyzed using Generalized Linear Models. Contrary to previous reports indicating a lunar influence on the flight activity of R. leschenaultii, our findings revealed that lunar phases had no significant effect on the flight activity of either R. leschenaultii or R. rouxii. In contrast, seasonal variation, particularly during the monsoon, was the primary driver of flight activity in both species. These findings highlight the importance of considering both species-specific responses and region-specific environmental conditions when developing conservation strategies for bats.