130 Pteromys volanscolor, especially on the tail, is much darker than in the
northern populations.
P. v. orii—island of Hokkaido (Japan). This form is similar to
P. v. volans. The underparts are pure white. The cheeks
are almost pure white. The tail is buff y on the margin
and blackish on the median.
conservation: IUCN status—least concern. Population
trend—declining.
habitat: This species is found in mature boreal closed-
canopy forests and is reported to be dependent on primary-
g row t h t rees. Thus it is sensit ive to log g i ng a nd severe forest
fragmentation. Various studies suggest, however, that the
maintenance of well-connected habitat patches that meet
this species’ requirements may allow it to persist in a land-
scape managed for timber harvests. The Siberian fl ying
squirrel shows a preference for mixed continuous forests
with old conifers (e.g., Norway spruce [Picea abies]) and nu-
merous deciduous trees, such as European aspen (Populus
tremula); the deciduous trees provide critical nest cavities. A
preference for spruce (Picea) over pine (Pinus) is also re-
ported. In Finland it has been shown that this species is
dependent on mixed forests that are dominated by spruce.
As the spruce component of the habitat declines, the prob-
ability of local extinction of P. volans increases. Increased
forest fragmentation has also contributed to its decline;
however, P. volans can reside in fragmented systems and
move reasonably well between forest fragments if adequate
corridors of vegetation exist and suitable habitat compo-
nents (e.g., spruce) are available in the matrix.
natural history: This species feeds heavily on buds,
leaves, fruit, catkins, twigs, lichen, and the mesophyll of co-
nifer needles; it is less partial to seeds. In particular, large
quantities of needles and leaves are reported to be con-
sumed daily, and it appears that individual squirrels have
preferred feeding trees. Occasional consumption of animal
material (e.g., eggs, juvenile birds, and small mammals) is
also reported. P. volans is reported to glide slowly (5–7 m/
second), but to exhibit considerable maneuverability be-
cause of its low wing loading. This species is generally noc-
turnal, but activity peaks vary with the light/dark cycle.
The animal may be active periodically, for up to 9 hours; it
can also be active during the day when day length is long,
despite lacking the color vision found in diurnal sciurids.
Male home ranges vary with landscape structure (between
20 and 135 ha), and it appears that P. volans can move reason-
ably well between forest fragments, provided adequate cor-
ridors of vegetation exist and suitable habitat components
(e.g., spruce) are available in the matrix. This species’ use of
habitat edges varies with the type of edges, overall land-
scape structure, and spatial scale.
Two peaks of reproduction are reported: one in March
and another in April–May. It is estimated that a third of the
animals in Finland breed twice annually, whereas those in
other parts of the range (e.g., Russia) may only breed once
annually, unless a female loses a litter. Gestation is 40–42
days; litter size is typically two to three, but can range from
one to four. Details of their development are described in
the literature. The young follow their mother during forag-
ing bouts. This species is unique in that it shows female-
biased juvenile dispersa l, which is best expla ined by compe-
tition between mothers and daughters for limited resources.
Mortality in juveniles appears to be highest prior to disper-
sal, rather than afterward. Relatively few predators, other
Pteromys volans. Photo courtesy Yushin Asari. than owls, are reported. At least two species of fl eas are
Pteromys volans. Photo courtesy Marko Schrader.