Trapping surveys of small mammals were made on 15 islands in the Inland Sea and on Shikoku from 11, October 2002 to April 2003. Apodemus speciosus was trapped on Yashirojima, Innoshima, Nakajima, Tajima, Yokosima and Shikoku Islands. Mogera wogura was trapped on Yashirojima Island and some mole tunnels were found on Nakajima I. A. speciosus was found in various habitats, but this species was not found in the orange orchards with bare ground surface.
It was shown that in the Inland Sea A. speciosus was generally found on the islands whose areas are over 13km² and often found on the other smaller islands connected to some of the bigger islands, including Honshu and Shikoku, by artificial bridges. It is suggested that A. speciosus may have dispersed through the bridges.