Lemurs

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Lemurs

Mouse and dwarf lemurs

True lemurs

Sportive lemurs

Indris or leaping lemurs

Aye-Aye, a superfamily of its own

Threats to lemur survival

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Lemurs are primitive primates, or prosimians, found only on the island of Madagascar and nearby small islands off the eastern coast of Africa. Although lemurs, lorises, and tarsiers are all prosimians, or “pre-monkeys,” only the lemurs and lorises have the typical prosimian snout that, like a dog’s, remains moist. This wet snout, called a rhinarium, suggests that scent is a particularly important sense to lemurs. Most lemurs, like other prosimians, also possess two built-in tools for grooming. The so-called “toilet claw” is located on the second toe of the hind foot (all other digits have a nail), and is used for picking through fur and eating. They also have a group of lower teeth (incisors) that combine into a horizontal tool called a dental comb, also used for grooming. All lemurs are nocturnal in habit.

Lemurs are classified in five families: the typical lemurs (Lemuridae); the sportive lemurs (Lepilemuridae); the dwarf and mouse lemurs (Cheirogaleidae); the indrids (Indriidae, including the indri, sifaka, and avahi); and the aye-aye, the lone member of Daubentoniidae.

The common name lemur means “ghost.” It was given to these elusive creatures by the famous eighteenth century Swedish biologist, Carolus Linnaeus.

Attracted by their large, bright eyes and strange calls, he thought they resembled the wandering spirits of the dead, called lemures in Latin (the language of science of the time). Linnaeus gave the name to many prosimians, but today the term lemur is used only for the prosimians of Madagascar and the Comoro Islands.

The lemurs of Madagascar were cut off from the mainstream of primate evolution at least 50 million years ago. In Madagascar, they evolved to occupy many ecological niches that, on the continent of Africa, were occupied by monkeys or apes. About 40 different species of lemurs evolved. Some, about as large as the great apes, are known only by their fossils.

Lemurs have flat nails instead of claws on both hands and feet. Most have 36 teeth, though the indrids have 30 and the ring-tailed lemur has 32. Many lemurs

exhibit profound differences in weight and activity from one season to the next. For example, the male’s scrotum, which holds the testicles, may enlarge as much as eight times as the mating season of summer approaches.

Mouse and dwarf lemurs

The smallest lemurs are called mouse and dwarf lemurs, family Cheirogaleidae. The smallest species is the lesser mouse lemur (Microcebus murinus ), which is about 5 in (12.5 cm) in length with an equally long tail. It weighs less than 2 oz (57 g). The brown lesser mouse lemur (M. rufus ) is slightly larger. Coquerel’s mouse lemur (irza coquereli ), the largest species in this group, is about twice as long. It is one of the rarest lemurs because its deciduous forest is being destroyed by logging and conversion to agriculture.

These little, large-eyed lemurs have long hind legs, useful for leaping. The lesser mouse lemur hops like a frog when on the ground. The females have three pairs of nipples, while true lemurs have only a single pair. They bear two or three tiny young (only about 0.2 oz [5 g] each) after a gestation period of about 60 days in the smaller species and 89 days in the larger.

Mouse lemurs survive the dry season, when food is scarce, by living off nourishment stored in their fat tail. Mouse lemur females share a spherical leaf nest with each other and their young, while males usually curl up by themselves. They all hunt at night as solitary individuals, eating primarily insects and some leaves, usually those bearing ant secretions. As they move about, they communicate with each other by high-pitched calls.

Mouse lemurs are active, busy creatures, while the dwarf lemurs (Cheirogaleus spp.) are rather sluggish all year. Dwarf lemurs are true hibernators, and are active only during the rainy season. The fat-tailed dwarf lemur (C. medius ) stores fat at the base of its

tail for use during its six-month hibernation. Dwarf lemurs are incapable of leaping from branch to branch, and they live in areas where the tree branches are closer together. Only the greater dwarf lemur (C. major ) resides in wet rainforest; the other three species live in drier forest.

The hairy-eared dwarf lemur (Allocebus trichotis ) was long thought to be extinct, but was rediscovered in 1965. Virtually nothing is known about it. The fork-marked dwarf lemur (Phaner furcifer ) has a dark stripe on its back which curves over the head and links up with the dark eye rings that mark all mouse and dwarf lemurs. Unlike Cheirogaleus, it is a great leaper, achieving distances of up to 33 ft (10 m) in a single bound.

True lemurs

The true, or typical lemurs (Lemuridae ) are diurnal primates and thus have relatively smaller eyes than

the mouse and dwarf lemurs. Their eyes are golden yellow. Their body is about the size of a domestic cat, but their tail is considerably longer. These lemurs eat fruit, leaves, and some insects. Their social groups vary in size from two to more than 20, and the females tend to dominate the males. The females also are responsible for defense of the group. The females usually bear a single offspring after a gestation period of about 18 weeks. The young lemur rides on its mother’s back for several months.

The fluffy, black-and-white striped tail of the ring-tailed lemur (Lemur catta ) is present in both males and females, though most lemurs exhibit sexual dimorphism, or different coloring in males and females. When moving, the ring-tailed lemur holds its dramatic tail up in a gentle curve. It also waves it to disperse the chemical released by its scent glands, which are located on its forearms. These glands have tiny spurs that can slash the bark of trees, leaving the slash scented with their territory-marking odor. The ring-tailed male also uses this scent in a strange kind of combat. When two aggressive males confront each other, each rubs its long tail on its forearm scent gland, turns, and waves its smelly tail. Apparently, one of the antagonists finds itself overwhelmed and gives in.

The ring-tailed lemur is about 15 in (38 cm) long, with an 18-20-in (46-51 cm) tail, and weighs about 6-7 lb (2.7-3.2 kg). Although ring-tailed lemurs spend most of their time on the ground (they are the only lemur that does this), they climb trees in their open forest in the early morning to reach the sunlight, which warms them after a chilly night. Because they spend much of their time walking on the ground, they have smooth, leathery palms and soles.

Only the male black lemur (L. macaco ) is completely black. Females have a white ruff around their black face and a white chest. The rest of the female’s body is reddish brown. The mongoose lemur (L. mongoz ) exhibits similar sexual dimorphism. Although males and females are both gray-brown in color, the females have white cheeks and neck, while the males have red cheeks. The widely occurring brown lemur (L. fulvus ) is a stay-at-home, rarely moving more than 300 ft (90 m) from its territory, which consists of only a few trees. Within this territory it tends to remain near the tops of the trees. It may be active day or night.

The largest of the true lemurs is the ruffed lemur (Varecia variegata ) of eastern Madagascar. It may be 4 ft (1.2 m) long from head to tail and weigh up to 6.5 lb (3 kg). Mostly a black animal, the long, shaggy fur of its ruff may be white or reddish. Its back and part of its legs are also white. Strangely, unlike the other true lemurs, the ruffed lemur has a fairly short gestation period (about 100 days compared to 120-135 days for the other species), and its offspring (often twins) are born too weak to hang onto their mother. She places them in a small fur-lined nest for at least three weeks.

The genus of so-called gentle lemurs (which are no more gentle than other lemurs), Hapalemur, prefers a watery habitat as well as forest. These lemurs live among the reeds located by lakes, and are sometimes good swimmers. They eat the soft heart, or pith, of the reeds, and they also like sugarcane. The gentle lemurs are more thickset than most lemurs. The broad-nosed gentle lemur (H. simus ) occurs in only three tiny populations and is critically endangered. The gray gentle lemur (H. griseus ) is more widespread but also threatened.

Sportive lemurs

Traditionally considered to be members of the Lemuridae, sportive lemurs were recently separated by some taxonomists into their own family, the Lepilemuridae, which includes seven closely related species. Sportive lemurs (Lepilemur spp.) received this name because, when threatened, they turn and raise their arms as if preparing to box. In their dry habitat, these lemurs eat primarily prickly succulent plants that provide so little nourishment that they eat their own feces to further digest the food (this is known as coprophagy). Unlike most lemurs, sportive lemurs live semi-solitary lives, with one male in a territory encompassing the smaller territories of several separated females. Sportive lemurs have 32 teeth as an adult instead of the 36 that true lemurs have.

Indris or leaping lemurs

The family Indriidae includes the two species of woolly lemurs or avahis, the indri, and three (or more) species of sifakas. These prosimians have only 30 teeth instead of the 36 found in most other lemurs. When on the ground, they primates tend to walk or leap upright.

The indri (Indri indri ) is the largest prosimian. Its name comes from a misunderstanding. Early explorers thought the natives were naming the animal when they said, “indri, indri.” Instead, they were exclaiming, “There it is” or “Look at that.” The indri is quite heavy, weighing more than 13 lb (6 kg) with a head plus body 27 in (69 cm) long. Unlike most prosimians, its tail is insignificant. It is black and cream in color, with an alert, humorous face. The cream color on its rump continues on down the back of its legs. However, some individuals do not have clear color differentiation. Indris live in groups that continually sing (actually closer to a “howl”) together, a sound that echoes through their tropical rainforest. They are a protected species, which is fortunate because they do not breed frequently. A female gives birth only once in two or three years.

The sifakas (Propithecus spp.) are soft, fluffy, and fairly large, at least 40 in (102 cm) in length including their long tail. Their whitish color is highlighted by a dark face and crown. Their name is an interpretation of the sound they commonly make. Sifakas often cling to vertical tree trunks and have legs and feet specially adapted for that position. Their legs are longer than their arms, and the big toe is especially long and strong for grasping. The diademed sifaka (P. diadema )of eastern Madagascar is quite rare and has not been studied to any extent; attempts to keep it in captivity have failed. The more common Verreaux’s sifaka (P. verreauxi ) is a territorial animal that marks its territory using glands located on the throat. The single offspring is carried on the mother’s stomach for several months before moving onto her back. The golden crowned sifaka (P. tattersalli ) of northeastern Madagascar was only described in 1988. It is one of the most endangered lemurs with fewer than 10,000 individuals surviving in the wild in small, fragmented populations.

The woolly lemurs, or avahis (Avahi spp.), are the smallest members of this family, being only about 12 in (30 cm) long, plus an equally long tail, and weighing about 2 lb (0.9 kg). Basically colored gray-brown, they have lighter rings around the eyes. Their major food comes from leaves, but they also eat flowers, and occasionally fruits and bark. Unlike the other indrids, the avahi is nocturnal, and its social groups include only three to five individuals.

Aye-Aye, a superfamily of its own

The aye-aye (Daubentonia madagascariensis ) is placed in a family, Daubentoniidae, by itself. It was given its friendly name by the first European to see it, Pierre Sonnerat, from the sound it makes. Looking rather like a squirrel with large eyes, it is about 3 ft (91 cm) long including its bushy tail. It has short, white fur beneath dark brown and white-tipped coarser fur. One of the prime reasons it is placed in a family by itself is that it has only 18 teeth. Instead of a dental comb, it has front incisors that, like a rodent’s, grow continuously.

Seen head-on, the aye-aye’s face looks triangular, made so by its large pointed ears and sharply pointed nose and chin. The aye-aye’s long grasping hands and feet have an extra-long middle finger with a hooked claw. This flexible digit is used clean insects from its

KEY TERMS

Dental comb —A group of lower incisor teeth on most prosimians that have moved together into a horizontal position to form a grooming tool.

Diurnal —Refers to animals that are mainly active in the daylight hours.

Grooming claw —A claw located on the second hind toe of many prosimians, used for grooming the fur.

Nocturnal —Active in or related to nighttime.

Rhinarium —The rough-skinned end of the snout, usually wet in prosimians, indicating that smell is important to them.

Sexual dimorphism —The occurrence of marked differences in coloration, size, or shape between males and females of the same species.

fur and as a probe to to scrape insect larvae, especially beetle grubs, from holes in wood. It also uses the claw on its long middle finger as a cup for drinking and for scooping coconut meat out of the shell. Aye-ayes lacks the toilet claw of other lemurs. Aye-aye females apparently breed only every other year or so. They are the only primates that have nipples located on the abdomen instead of on the chest.

A larger aye-aye (D. robusta ) became extinct probably less than 1,000 years ago. Daubentonia madagascariensis was thought to be extinct after 1930, but was rediscovered in 1957 in the eastern rainforest. The aye-aye was once considered one of the most endangered mammals in Madagascar, but scientists now believe that it is elusive rather than very rare. The species is found in several protected areas in Madagascar. An uninhabited island, Nosy Mangabe, is a protected reserve for this species. In the 1960s, nine aye-ayes were captured and taken to this island, where they have established a small population.

Threats to lemur survival

At least 14 species of Madagascar lemurs have become extinct since humans colonized the island about 2,000 years ago. The remaining species are all in danger of extinction as the human population continues to expand, requiring space, food, and firewood. Lemur species that eat a relatively wide variety of food will be more likely to survive as their habitat diminishes.

Lemurs are protected by Malagasy law, but they are still often hunted as a delicacy. Some lemurs are killed for superstitious reasons, but others are protected for the same reasons. For example, some tribes believe the indri takes on the souls of their ancestors, therefore they are opposed to killing these lemurs. On the other hand, some tribes regard the presence of an aye-aye near a village as a signal of coming death, and they quickly kill these animals when they find them.

All lemurs need protection, as does their remaining habitat. Some species can be bred in captivity. Successful captive-breeding programs have been established for the black lemur and the ruffed lemur, with the hope of returning the offspring to Madagascar. Indris and aye-ayes, on the other hand, have proved very difficult to maintain, let alone breed, in captivity.