Night Explorers of Kemuning Forest: Javan Flying Squirrel

Flying may not be something extraordinary for winged animals like birds. However, for a squirrel, soaring through the air is a different matter. The ability to glide is only possessed by a small number of squirrel species that belong to the group known as gliding mammals.

Gliding is not the same as flying. Essentially, gliding only prolongs the effect of gravity without enabling upward vertical movement while in the air.

One species of gliding mammal found in Indonesia is the Javan flying squirrel (Iomys horsfieldii). This species, also known locally as walangkopo, can be encountered particularly at night in Kemuning Forest, Temanggung, Central Java.

Javan Flying Squirrel

Like other flying squirrels, the Javan flying squirrel has a thin membrane of skin called a patagium, which connects its forelimbs and hindlimbs, allowing it to glide through the air. This patagium is slightly darker than the rest of its body.

The Javan flying squirrel also has relatively large eyes and ears, along with long claws that help it grip tree trunks and branches.

Its body is generally orange-brown to grayish-brown, with a tail that is slightly lighter on the ventral surface and sides. The average body length is about 182 mm, and the tail is equal to or slightly longer than the body length.

The patagium, resembling the wing of an aircraft, enables the squirrel to glide through the air

There is limited information regarding sexual dimorphism in the Javan flying squirrel. However, in related genera such as Hylopetes and Petinomys, males and females show little difference in appearance, suggesting that Javan flying squirrels likely exhibit similar characteristics between sexes.

Several subspecies of the Javan flying squirrel have been identified, although only a limited number of specimens have been studied to confirm these distinctions.

Iomys horsfieldii davisoni has dark grayish-brown fur and a dark brown tail with reddish-brown speckles and shorter tooth rows. Iomys horsfieldii penangensis has lighter coloration and longer tooth rows. Iomys horsfieldii thomsoni is very similar to I. h. davisoni, but its tail is uniformly reddish-brown without speckles. Recent information suggests that Iomys horsfieldii horsfieldii is distinct from these subspecies, bringing the total to at least four recognized subspecies.

Behavior

The Javan flying squirrel is nocturnal, meaning it is active at night, and arboreal, spending most of its time in the forest canopy. Like other flying squirrels, it can glide long distances between trees and uses its long claws to land and cling to surfaces.

Very little is known about its social behavior. However, related species in the genus Petaurista have been observed living either alone or in small groups, suggesting that the Javan flying squirrel may exhibit similar behavior.

Geographic Distribution

The geographic range of the Javan flying squirrel is limited to Southeast Asia. Its natural distribution extends from the Malay Peninsula to Sumatra, Java, and Borneo, with additional records in Singapore, Tioman, and Penang.

Habitat

The Javan flying squirrel is relatively adaptable and can be found in a variety of habitats. It inhabits different forest types, including degraded forests. It can also be found in shrublands and even in agricultural areas such as durian plantations. It typically shelters in tree hollows.

There is limited information about its diet. However, related species in the genus Petaurista feed on fruits, nuts, and shoots. Therefore, it is likely that the Javan flying squirrel has a similar diet, being both herbivorous and frugivorous.

Ecological Role

Little is known about the ecological role of the Javan flying squirrel. However, as a likely herbivore and frugivore, it may contribute to seed dispersal within its ecosystem. On the other hand, it may also act as a pest in nurseries or agricultural plantations.