Japan's Flying Squirrels: Two Species, Night Gliders of the Forest

Japan hosts two native species of flying squirrels, both nocturnal, arboreal, and equipped with a patagium (gliding membrane) stretching from wrists to ankles. They are not true fliers but expert gliders—covering up to 50–100 meters between trees.

1. Siberian Flying Squirrel (Pteromys volans)

• Japanese Name: Ezo-momonga (エゾモモンガ)
• Range: Hokkaido, northern Honshu (north of Chubu), Sakhalin, Kurils, Siberia, N. Europe.
• Size: Body 15–18 cm; tail 11–13 cm; weight 100–150 g.
• Appearance: Gray-brown back, white belly; large black eyes; flattened, bushy tail (rudder).
• Habitat: Sub-boreal coniferous/mixed forests; tree cavities, old woodpecker holes.
• Diet: Seeds, buds, leaves, bark, fungi, insects; caches food.
• Status: Least Concern (IUCN); locally declining due to logging.

2. Japanese Dwarf Flying Squirrel (Pteromys momonga)

• Japanese Name: Nihon-momonga (ニホンモモンガ)
• Range: Honshu (central/south), Shikoku, Kyushu. Endemic to Japan.
• Size: Body 12–14 cm; tail 9–11 cm; weight 70–100 g. Smaller, rounder.
• Appearance: Brown-gray back, white belly; smaller eyes; shorter, fluffy tail.
• Habitat: Temperate broadleaf/conifer forests; similar nesting.
• Diet: Similar; more fruit/insects.
• Status: Least Concern; habitat fragmentation a concern.

Ecology & Behavior

• Nocturnal: Active 30 min after sunset – before dawn.
• Gliding: Launch from high branch; spread patagium; control with tail/limbs; land vertically on trunk.
• Social: Often share nests (family groups); communicate with ultrasonic calls.
• Predators: Owls (Ural, Blakiston's fish owl), martens, snakes, cats.

Cultural Presence

Momonga are beloved in Japan—mascots, anime (e.g., Chiikawa), regional tourism (Hokkaido night tours). They symbolize forest health.

Seeing one requires a guided night hike in Hokkaido (Ezo-momonga) or Honshu/Shikoku/Kyushu forests (Nihon-momonga).