Tree Shrews

The tree shrews (order Scandentia, family Tupaiidae) comprise a small number of species that are only found in South and Southeast Asia. Five genera (19 species) are recognized. All occur in forested areas, ranging from India and Southwest China eastward through Malaysia, Indonesia (west of Wallace's Line), and the Philippines. Three genera and 10 species occur on the island of Borneo alone.

In appearance, tree shrews resemble long-snouted squirrels (the Malay word tupai means squirrel). All tree shrews are of a slender build; adults generally weigh 2.5-3.5 oz (70-100 g.) The length of the head and body ranges from 3.9-8.6 in (100-220 mm), while tail length varies from 3.5-8.8 in (90-225 mm). Generally a russet-brown color, they have a long, pointed muzzle with 38 sharp teeth. One unusual species, the pen-tailed tree shrew (Ptilocercus lowi), can be identified by its tail, which is naked except for a whitish feather-shaped arrangement of the hairs near the end. In all species, the fur consists of long, straight guard hairs and shorter, softer underfur. Some forms have pale shoulder stripes and others have facial markings. The ears are squirrel-like; that is, they are comparatively small and cartilaginous, except in the pentailed tree shrew in which they are larger and more membranous. The feet of tree shrews are naked beneath; the soles are adorned with tubercle-like pads which assist with climbing. The long and supple digits bear sharp, moderately curved claws. Tree shrews have well developed senses of vision, hearing, and smell.

In addition to their external resemblance to squirrels, tree shrews, like squirrels, are mostly diurnal, and some of their actions and movements are similar. Ptilocercus differs in being mainly nocturnal and, when on the ground, progresses in a series of hops. Other tree shrews are swift runners. All tupaiids are capable climbers, seeking their food in trees as well as on the ground. Their diet consists mainly of insects and fruit but occasionally includes other animal food and various types of plant matter. They are generally fond of water for both drinking and bathing. Most species nest in holes in tree trunks or branches 65.7-98.4 ft (20-30 m) high, the nest consisting of a simple structure of dried leaves, twigs, and fibers of soft wood.

Few other mammalian families have proved as difficult to classify as the tree shrews. Historically, the Tupaiidae have been grouped with the Macroscelididae (elephant shrews), Insectivora (insectivores), and even the primates. More recent studies of their behavior and reproduction, however, has led to them being placed in a distinct order, Scandentia.

Tree shrews display a wide range of social behaviors. The common tree shrew Tupaia glis, for example, lives in permanent pairs, with males occupying an average home range of 12,168 sq yd (10,174 sq m) and females a smaller area of about 1,052 sq yd (880 sq m). Although they basically share the same range, they remain largely solitary and defend the area from possible intruders. In contrast, the pen-tailed tree shrew generally moves about in pairs, but as many as four animals have been found together in a single nest. Field observations also suggest that many species exist at relatively low densities: data for T. glis show a varied pattern of one to two per acre (two to five per hectare) in Malaysia or two to five per acre (five to 13 per hectare) in Thailand, while T. palawanensis occurs at a local density of 0.5-1 per acre (1.5-2.5 per hectare).

Scent marking plays an important role in communications among tree shrews, all of which have specialized glands that secrete a wide array of chemical compounds, many of which are unique to the individual animal. The different compounds in these secretions covey a range of messages about the animal, particularly information on its sex, age, and breeding status. Such information is thought to play an important role in defending individual territories. Tree shrews seem to be creatures of habit and regularly use the same paths along the ground or on branches to reach their favorite feeding or resting areas. As they move around their ranges, their scent is liberally deposited, usually at strategic places where other animals have a chance of finding it. In this way, an intruding animal will be able to determine that the area is already occupied and defended by a resident tree shrew and should be able to withdraw without further conflict. If the intruder is a male, hoping to mate or take over the territory of a neighboring animal, it may move further into the territory, but on doing so risks attack and possible injury from the resident animals.

The reproductive behavior of most species is still poorly known. Most species apparently breed throughout the year. Following a gestation period of about 45-50 days, females give birth to one to four young. Some species, such as Urogale everetti, are receptive to breeding again shortly after giving birth.

Surprisingly, in view of their large size and diurnal habits, tree shrews have attracted relatively little biological attention. As a result there has been little study of their ecology or behavior in the wild. All tree shrews are forest-dwelling species, occupying a wide range of niches within different forest habitats. Many species seem capable of adapting to living in secondary forest and some even occur in rural gardens and well-established plantations.

Tropical forests are, however, their preferred domain, and because of their dependence on forest habitat, many of these species are susceptible to excessive levels of clearance and disturbance. Some species, particularly Tupaia nicobarica and T. longipes, are thought to be endangered, but other species with restricted ranges, particularly those on islands or where agricultural encroachment and/or logging is a major activity, are also seriously threatened. The most urgent among these are the golden-bellied (Tupaia chrysogaster), Palawan (T. palawensis), Philippine (Urogale everetti), and Madras (Anathana elliotti) tree shrews. Although loss of habitat is the main threat to these species, additional pressures such as hunting for food and sport can add to the pressure on these and other native endemic species. Habitat conservation is therefore vital to preserving tree shrews.

The forests that are important to tree shrews are also known to be of great importance to a wide range of plants, mammals, birds, and invertebrates, many of which are endemic. By developing and implementing conservation strategies which include tree shrew conservation requirements in these forests, the overall biological diversity of these unique ecosystems could be far better protected. These same forests also fulfill many other essential roles that benefit humans, particularly through watershed protection and as an important source of fruit, medicinal and herbal plants, and a wide range of timber products of economic importance.

In view of the many uncertainties surrounding the ecological status, distribution, and ability of these species to adapt to secondary habitats, there is an urgent need to promote further action for a large number of these species. Particular aspects which need attention include details of the basic ecology, home range size, feeding priorities, habitat preferences, breeding behavior, and population density of most species.