Seasonality in the flight activity of the tropical bat Rhinopoma hardwickei under natural photoperiod

The activity cycle of a colony of about 1500 bats Rhinopoma hardwickei was studied in 1978-1979 in Madurai, India. Variations in the times of emergence of foraging paralleled variations in sunset and return to the roosting paralleled sunrise. The releasing stimulus for departure of the first outflyer on clear evenings is the crossing of a lower threshold value of its relative decrease. Return to the roost usually occurs at a lower light intensity than the departure. In summer the nightly rate of emergence is relatively higher than in winter. The seasonal changes of phase angle differences of onset (Ψ0) and end (Ψe) of activities are roughly mirror images. The time of midpoint of foraging activity however, stays relatively constant.