Yuri Shibnev / Siberian flying squirrel (Pteromys volans) on tree trunk, Ussuriland, South Primorskiy, Far East Russia

Benjam Pontinen / Siberian flying squirrel in nest {Pteromys volans} Finland.

Benjam Pontinen / Siberian flying squirrels in nest {Pteromys volans} , Finland.

Yuri Shibnev / Siberian flying squirrel food hoard (Pteromys volans) Russia Ussuriland, South Primorskiy

Benjam Pontinen / Siberian flying squirrel looking out of nest hole in tree {Pteromys volans} Finland, Europe

Benjam Pontinen / Siberian flying squirrel feeds in alder tree. Nurmo, Finland.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) emerging from nest hole in tree at dusk. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) eating buds in tree. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) feeding on Sakhalin fir tree. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) sitting in tree at dusk. Hokkaido, Japan. March.

Tony Wu / Siberian flying squirrel (Pteromys volans orii) emerging from nest hole in tree trunk. Hokkaido, Japan. March.

Nick Upton / Felled conifer trees stacked beside forestry track through mixed forest. Near Muraka Forest Reserve, a rare surviving home for Siberian flying squirrel (Pteromys volans). Near Lisaku, Estonia. April 2...