The greater horseshoe bat, Rhinolophus ferrumequinum, is a large cave-dwelling bat and is commonest among cave-dwelling bat species in Japan. Cave-dwelling bats are very sensitive during the maternity season, and disturbance to maternity colonies often results in a serious impact on regional populations. However, a casual observation revealed R. ferrumequinum overcame serious accidental human disturbance by securing a new maternity cave and forming a new colony. The ability of R. ferrumequinum to respond flexibly to unexpected disturbance may be advantageous for the prosperity as the dominant Japanese cave-dwelling bat.