Siberian Flying Squirrel

The Siberian flying squirrel is a small nocturnal flying squirrel ranging from northern Europe across Russia to Japan. It glides between trees using a furred membrane stretched between its limbs, and feeds on seeds, buds, leaves, and catkins, especially from birch and alder.

The Siberian flying squirrel (Pteromys volans) is strictly nocturnal, emerging shortly after sunset to begin a night of foraging, gliding, and nest-visiting activity before retreating to a tree cavity or dense nest well before dawn. This nocturnal rhythm reduces competition and predation risk from diurnal birds of prey while aligning with the activity patterns of the moths and other insects that occasionally supplement its diet. During the coldest winter months in Siberia and Fennoscandia, individuals may enter short bouts of torpor, remaining inactive in insulated nests for several days during extreme cold snaps rather than undertaking true hibernation.

Socially, this species is largely solitary outside of the breeding season and brief periods of communal winter nesting, where several individuals—often related females—may huddle together in tree cavities to conserve body heat. Home ranges vary considerably by habitat quality and food availability, typically spanning 1–10 hectares for females and larger overlapping ranges for males, who roam more widely in search of receptive mates. Scent marking via glandular secretions on branches and tactile communication during rare social encounters play key roles in mate location and individual recognition, while soft vocalizations, including chirps and squeaks, are used at close range, particularly between mothers and offspring.

The species’ most striking adaptive behavior is gliding, enabled by the patagium—a furred membrane stretching between the wrists and ankles—which allows controlled aerial descents of over 50 meters between trees, with the flattened tail acting as a rudder and brake. This adaptation minimizes time spent on the vulnerable forest floor and enables efficient movement through the multi-layered canopy of boreal and mixed forests, an essential trait for a species reliant on old-growth trees with abundant cavities for nesting.

As an herbivore, the Siberian flying squirrel forages primarily on tree buds, catkins, seeds, and young leaves, with birch (Betula) and alder (Alnus) catkins forming a dietary cornerstone throughout much of its range across Fennoscandia and Siberia. It also consumes conifer seeds, particularly from spruce (Picea) and pine (Pinus), along with occasional fungi, lichens, and, opportunistically, bird eggs or insects when plant material is scarce. Foraging occurs almost exclusively in the canopy, with individuals gliding between feeding trees rather than descending to the ground, a strategy that reduces predation exposure and energy expenditure compared to terrestrial locomotion.

Seasonal dietary shifts are pronounced: spring and summer diets emphasize fresh leaves, buds, and developing seeds, while autumn brings a shift toward energy-dense seeds and nuts that are often cached in tree hollows to sustain the squirrel through winter scarcity. In winter, cached food and available conifer seeds and dormant buds become critical, and metabolic slowdowns combined with periods of torpor help conserve energy when high-quality forage is limited. The species obtains most of its water needs from succulent plant material and morning dew, showing minimal dependency on standing water sources given its arboreal, canopy-restricted lifestyle.

Breeding in the Siberian flying squirrel typically occurs twice a year, with peaks in early spring (March–April) and sometimes a second cycle in mid-summer, depending on latitude and food availability. The mating system is promiscuous, with males competing for access to receptive females through scent-tracking and range overlap rather than forming pair bonds. Following a gestation period of approximately 30–35 days, females give birth to litters of two to four altricial young in a well-insulated tree cavity nest, often lined with lichen, moss, and shredded bark for thermal protection.

Maternal care is intensive and exclusive to females, who nurse, groom, and defend the young for roughly two months, with weaning occurring around 5–6 weeks of age as juveniles begin to explore short glides near the nest. Sexual maturity is reached at approximately one year of age, and while first-year survival is variable due to predation and winter mortality, females that survive to breeding age can reproduce annually for several years, contributing to relatively stable local population dynamics in undisturbed old-growth habitat.

The primary threat to the Siberian flying squirrel is habitat loss and fragmentation driven by commercial logging of old-growth and mature mixed forests, which eliminates the large-diameter trees with cavities essential for nesting and reduces the continuous canopy needed for gliding between feeding sites. In parts of its European range, particularly Finland and the Baltic states, intensive forestry practices have led to localized population declines and range contraction, prompting the species’ listing under the EU Habitats Directive despite its global “Least Concern” status. Climate change poses an emerging concern, as shifting precipitation and temperature patterns may alter the timing and availability of key food resources like catkins and seeds, potentially desynchronizing breeding cycles from optimal forage windows.

Natural predators include owls (particularly Ural and tawny owls), pine martens, and occasionally goshawks, with nest predation by martens representing a significant source of juvenile mortality. Human-wildlife conflict is minimal given the species’ nocturnal, arboreal habits and lack of agricultural impact, though incidental habitat disturbance from infrastructure development remains a low-level pressure. Conservation initiatives, including retention of old-growth forest patches, nest box programs in managed Fennoscandian forests, and protected area designations across its Russian and Chinese range, have helped maintain stable populations, and the species continues to be monitored under national forestry biodiversity assessments in several European countries.

• Living Gliders, Not Fliers: Despite the name, Siberian flying squirrels don’t truly fly—they glide using a furred membrane called the patagium, achieving controlled descents of over 50 meters between trees.
• Nocturnal Navigators: Their large, light-sensitive eyes are a key adaptation for nighttime foraging and precise depth perception during high-speed glides through dense forest canopy.
• Rudder Tail: The flattened, furry tail acts as both a stabilizer and brake during flight, allowing sharp mid-air turns to avoid branches and predators.
• Ancient Lineage: Pteromys volans belongs to one of the oldest surviving flying squirrel genera, with fossil relatives dating back millions of years in Eurasian forests.
• Legally Protected in the EU: Although globally classified as Least Concern, this species is strictly protected under the EU Habitats Directive due to regional population sensitivity in Finland and the Baltics.
• Winter Torpor Strategy: Rather than true hibernation, individuals enter short torpor bouts during extreme cold, huddling communally in tree cavities to conserve energy.
• Silent Seed Caching: Like many squirrels, they cache seeds and nuts in autumn, inadvertently aiding forest regeneration by dispersing uneaten seeds across their home range.