Diurnal activity in an insectivorous bat during migration period.

The article investigates diurnal flight activity in the Common Noctule bat (Nyctalus noctula) in Central Europe, proposing that such daytime flights are primarily linked to the species’ migratory behavior rather than disturbance, food shortage, or predator absence. Using over 500 community-science records documenting more than 15,000 bats, the study found that diurnal activity peaks during spring and autumn migration periods, with autumn flights showing significant southward directional movement and higher flight altitudes. Seasonal body mass data indicated that increased diurnal activity in autumn coincides with higher body mass, challenging hypotheses that link early roost emergence to poor condition or predation risk. The findings suggest that partial diurnal activity during migration may help Common Noctules meet elevated energetic demands by foraging on abundant daytime prey while conserving nighttime for long-distance flights, and that mapping diurnal flight occurrences could aid in identifying bat migration corridors.