The Hawaiian hoary bat, Aeorestes semotus, is a light reddish gray and averages less than 4.5 in (11 cm) in length. When it moves, the bat's colouration appears to ripple as the darker underfur is exposed. This subspecies is smaller and more reddish than related mainland forms. It and the endangered Hawaiian monk seal (Monachus schauinslandi) were the first mammals to establish populations on the Hawaiian Islands.