106 Iomys horsfi eldiiIomys horsfi eldii (Waterhouse, 1838)
Javanese Flying Squirrel
description: This fl ying squirrel is brown on the back,
and the tail is reddish. It has a black eye ring with a short
black stripe extending to the base of the whiskers. The ven-
tral surface is orange buff. (The description is based on a
specimen from the island of Borneo.)
size: Female—HB 189.6 mm; T 179.6 mm; Mass 209.8 g.
Sex not stated—HB 191.8 mm; T 176.5 mm; Mass 165.3 g.
distribution: The range of the Javanese fl ying squirrel ex-
tends across peninsular Malaysia to Sumatra and Java (Indo-
nesia) and the island of Borneo (divided among Malaysia,
Brunei Darussalam, and Indonesia). It is also found in Tio-
man and Penang islands (Malaysia), but it may now be ex-
tinct in Singapore.
geographic variation: Four subspecies are recognized.I. h. horsfi eldii—Java and Sumatra (Indonesia). The upper-
parts are rufous brown, and the underparts are yellow or
yellowish white. The underside of the tail is bright rust.
The margin of the fl ank skin is reddish yellow, as are the
sides of the face below the eyes.
I. h. davisoni—peninsular Malaysia and Singapore. The color
on the back is dark slaty gray with rufous orange hair
tips, and the edges of the sides are lined with rich orange.
The tail is rich brown above and rich rufous orange
below.
I. h. penangensis—Penang Island (Malaysia). Similar to I. h.
davisoni, but I. h. penangensis is lighter and brighter on the
dorsal surface, hands, feet, and tail.
I. h. thomsoni—island of Borneo (divided among Malaysia,
Brunei Darussalam, and Indonesia). The upperparts and
head are a dark smoky brown grizzled with dull buff y
white. The undersides are whitish or pale fulvous.conservation: IUCN status—least concern. Population
trend—stable.habitat: This species uses a broad range of habitats, in-
cluding forest stands of all ages, disturbed and scrub vegeta-
tion, forest edges, and a variety of plantations, where it is
sometimes considered a pest. It appears to be less common
in dense forests, and it generally occurs at elevations below
1000 m.Iomys Thomas, 1908
This genus contains two species. Based on both morpho-
logical and sequence data, fl ying squirrels are considered to
have diverged into two main clades. Iomys is a member of
the Glaucomys clade, which includes Eoglaucomys, Glaucomys,
Hylopetes, Iomys, Petaurillus, and Petinomys.Iomys horsfieldii. Photo courtesy Norman Lim.