Pteromys volans orii . A preliminary survey on nest cavity use by Siberian flying squirrels, Pteromys volans orii , in forests of Hokkaido Island, Japan . ... Pteromys volans orii , which is an endemic subspecies to Hokkaido Island, Japan, is arboreal and usually nests in cavities in trunks. To broadly understand what nest cavity is selected by P. volans orii in mountainous areas, we preliminary surveyed cavity resources in natural forests of Hokkaido. All nest cavities were on live-trees. ...