Lorises

Lorises move in very deliberate fashion, with none of the free-wheeling abandon of many other primates. Moving among the branches of trees at night is serious business. They make sure that one hand is well anchored before moving the next one. They also make the movements with incredible smoothness, disturbing nothing around them. This keeps them from being seen by predators as they move through the dense tree tops. They can remain absolutely motionless for many hours at a time, a technique that is very effective in staying alive. They also have to remain silent, otherwise their high-pitched twitter can reveal their presence.

A loris's opposable thumb is even more specialized than the thumbs of most primates. It has moved almost exactly opposite the last three fingers, and the first finger has almost disappeared. This arrangement is handy for a tight grip on the high branches in the forest canopies in which they live. Lorises are generally solitary creatures, though they may hunt in pairs or family groups.

The slender loris (Loris tardigradus) of southern India and Sri Lanka has round eyes that look larger than they are because they are set in pear-shaped patches of dark fur on their lighter-colored triangular faces. This primate is called the slender loris because its body is much thinner than the well-rounded slow loris. It has comparatively long arms and legs.

A slender loris (Loris tardigradus) in Asia. Photograph by Ron Austing. The National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission.

The two species called slow lorises are indeed slow, moving very carefully and deliberately among the trees. They are plumper than the slender loris. The somewhat larger slow loris (Nycticebus coucang) of Southeast Asian islands Java and Borneo has a dark strip up its back and a white patch on its head and upper back. The slow loris is rapidly disappearing wherever its forest habitat is being disturbed, although it is legally protected throughout most of the countries where it lives. The pygmy slow loris (Nycticebus pygmaeus) of Vietnam and Laos is only about 7.5 in (19 cm) long. It is round and woolly with large, close-set eyes. It is sometimes regarded as a subspecies of slow loris.

The larger potto (Perodicticus potto) lives in Guinea, Zaire, and Kenya. It may weigh more than 2 lb (1 kg). Its tail is visible beyond its silky fur, unlike the slow loris's, which is not long enough to show. Also, the potto has three or four unusual skin-covered bony spines behind its neck. When threatened, the potto clings tightly to its branch, tucks in its head, and turns these spines to the attacker, which can be taken by surprise because the spines are hidden in the pott's dense fur. If not left alone because of its spines, a potto can curl its head under its body and give a ferocious bite. In their homelands, pottos are famed for the strength of their grip.

Pottos generally live solitary lives, but the male in an area inhabited by several females keeps track of their readiness to mate by following their urine trails. After a period of getting acquainted, they may mate while hanging upside down from a branch. They have a longer gestation period than most prosimians, 193 days. This produces a baby mature enough to cling to the moving mother almost immediately after birth.

Closely related to the potto, but inhabiting the shrubs of the forests of Gabon, Congo, and Zaire instead of the high canopy, is the angwantibo, also called the golden potto (Arctocebus calabarensis). The angwantibo is much smaller than the potto, about 10 in (25 cm), as opposed to about 14 in (36 cm), and it lacks the tail and the neck spines. Even from birth the golden potto exhibits its skill in clinging upside down. The mother "parks" her infant upside down on a branch while she goes about her nocturnal eating. When she returns, she anchors herself around the baby, also upside down. The baby releases itself from the branch and clings right side up to her stomach. A mother angwantibo continues to nurse one infant until just before the next one is born.