EASTERN LESSER BAMBOO LEMUR
Geographic Distribution and Habitat
The eastern lesser bamboo lemur (Hapalemur griseus), also known as the gray bamboo lemur, the gray gentle lemur, and the Mahajanga lemur, is native to the large island country of Madagascar. Regarded by conservationists as a world biodiversity hot spot—home to species found nowhere else in the world—Madagascar is situated about 249 mi (400 km) off of Africa’s southeastern coast in the Indian Ocean.
As its name hints, eastern lesser bamboo lemurs are predominantly found in the eastern region of Madagascar. They dwell south of the Mangoro and Onive rivers within Ranomafana National Park. These primates are also found in western Madagascar between the Mahavavy and Tsiribihina Rivers. Previously, this geographic range had been assigned to the western bamboo lemur (Hapalemur occidentalis).
The largest populations occur near stands of bamboo and bamboo vines within primary and secondary forests. Tropical moist lowland forests, montane forests, and areas of marshland further define the species’s habitat. The lemurs reside at altitudes up to 6,726 ft (2,050 m). Air temperature ranges from 39.2 to 86 F (4–30°C), with an average of 69.8 F (21°C) and high humidity.
Lemurs belong to the oldest and most primitive order of primates, known as prosimians, and to the suborder, known as Strepsirrhine. Others belonging to this order/suborder include galagos (or bush babies), lemurs, lorises, pottos, and tarsiers.
Several subspecies of the eastern lesser bamboo lemur have been identified. Each one exhibits subtle variations in coat color and each occupies its own (sometimes overlapping) geographic range in Madagascar. Over the last two decades, however, scientists have debated the veracity of some of these subspecies, elevating two, the Lac Alaotra bamboo lemur (Hapalemur griseus alaotrensis) and the western lesser bamboo lemur (Hapalemur griseus occidentalis) to full species status in 2001, and elevating Gilbert’s lesser bamboo lemur (Hapalemur griseus ssp. Gilberti) to full species status in 2008. Scientists also transferred H. simus to the genus Prolemur.
The subspecies Ranomafana bamboo lemur, H. g. ranomafanensis, discovered in 2007, has been questioned. Some scientists argue that a subspecies status is impossible to declare because this primate’s genetic variation with the eastern lesser bamboo lemur has not been ascertained.
After all the shuffling between species/subspecies status, the transferring of genus classification, and various debates, two subspecies of the eastern lesser bamboo lemur appear to remain uncontested: Hapalemur griseus griseus and Hapalemur griseus meridionalis.
Size, Weight, and Lifespan
Of the nearly 60 taxa of lemurs (including species and subspecies) who make Madagascar their home, eastern lesser bamboo lemurs are in the small- to medium-sized range and they are the smallest of the bamboo lemur species. They have an average head-to-body length of just over 2 ft (66 cm), an average weight of just over 2 lb (0.935 kg), and a tail that is longer than their bodies. Males are typically slightly larger than females.
Lifespan in the wild is unknown. However, the leading cause of death in the wild is known to be predation (by both natural predators and humans), followed by human-caused habitat loss. In captivity, the average lifespan for females is 17.1 years and for males is 12.8 years. The maximum age documented (sex not given) for a captive eastern lesser bamboo lemur is 23 years.
Refers to mothers leaving their young alone, in a safe location, while they go off to forage.
Having only one sexual partner.
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Eastern lesser bamboo lemurs have small, compact bodies with shorter forearms than hindlimbs. Nature has draped them with a dense gray coat, tinted with cinnamon-colored fur on their back. They also wear a cinnamon-colored fur cap on the crown of their head. Scalloped ears, the outer sides of which are furry gray, sit close to either side of their cinnamon crown. Large brown eyes assess the world. A long snout narrows to two moist, black, demur nostrils. The fur on their face is closely cropped. Hands and feet are black and hairless, and their long tail is nonprehensile.
Befitting their name, eastern lesser bamboo lemurs eat lots of bamboo—75–90% of their diet is comprised of this woody, flowering perennial. Of the more than 40 species of bamboo provided to them by their habitat, eastern lesser bamboo lemurs favor the giant bamboo (Cathariostachys madagascariensis) plant.
They feed through one side of their mouth and chew the bamboo on the other side. New shoots (specifically, the base and inner walls of young bamboo shoots) are preferred. Only during winter months, when new shoots are scarce, will the lemurs eat the bamboo plant’s mature leaves and its hollow stem. The species is known to practice geophagy, the eating of earth to attain necessary mineral nutrients. Grass stems, assorted berries, and young leaves of other plants, particularly the creeping lianas (long-stemmed woody vines) supplement eastern lesser bamboo lemurs’ diet. Females typically eat more than males to cope with the biological stress of gestation and lactation.
Fresh bamboo, scientists know, is toxic due to high levels of cyanide found throughout the plant; the shoots are especially toxic. Yet, somehow, bamboo lemurs do not experience cyanide poisoning. Scientists do not know how this detoxification phenomenon occurs.
Madagascar’s golden bamboo lemurs (Hapalemur aureus), who are Critically Endangered, are even more adept at detoxifying cyanide within their bodies, ingesting about 18 oz (500 g) of cyanide-laden bamboo each day—or about 12 times the lethal dose per their body mass. And the island country’s Critically Endangered greater bamboo lemurs (Prolemur simus, formerly known as Hapalemur simus), the largest of the bamboo lemurs, also processes cyanide with no ill effect. All three species (eastern lesser bamboo lemur, golden bamboo lemur, and greater bamboo lemur) occupy territories within Ranomafana National Park. Scientists speculate that because each species favors a different part of the bamboo plant—and because eastern lesser bamboo lemurs prudently avoid bamboo plants with the highest levels of cyanide, easily tolerated by golden bamboo lemurs—territorial disputes among the three species are avoided.
An unrelated species that has mastered cyanide detoxification is China’s giant panda. These oversized bamboo-eating “teddy bears” are able to convert 80% of absorbed cyanide into a less toxic chemical, called “thiocyanate,” which the bears excrete through their urine.
Behavior and Lifestyle
Diurnal primates (active during daylight hours), eastern lesser bamboo lemurs while away a huge chunk of their day eating bamboo. Those full bellies lead to long naps. Travel accounts for the least amount of their time, or expended daily energy. Unlike other lemurs, who employ a “search and sniff” foraging strategy in determining a tasty food morsel, eastern lesser bamboo lemurs remain stationary and scan the nearby foliage for tender bamboo shoots. When foraging, they rely on their impressive manual dexterity and superior hand-to-eye coordination to leap from bamboo stalk to bamboo stalk or from tree trunk to tree trunk. Although they are mostly arboreal (spending most their time in trees) and may hang out on a particular tree by vertically clinging to it, eastern lesser bamboo lemurs descend to the ground occasionally, to drink water, for example. On the ground, they travel quadrupedally, using all four limbs. The species’s manner of traveling on the ground has been likened to that of a small cat, galloping along. At dusk, eastern bamboo lemurs retire to their arboreal sleeping sites for the night.
Scientists speculate that lemurs floated from mainland Africa to the island of Madagascar eons ago on rafts of vegetation.
“Lemur,” the genus name, means “ghost” or “spirit of the night” in Latin. Legend holds that 16th century Portuguese explorers to Madagascar were awakened, deep into the night, by the lemurs’ howls. The animals’ flickering eyes further convinced the unhinged explorers that these beings were the ghosts of their dead companions. Thus, they dubbed these ethereal creatures “lemurs.”
Eastern lesser bamboo lemurs live in social family groups (or troops). Troop size ranges from three to six individuals and may include more than one breeding female. Unlike males, who leave their natal (birth) group upon reaching adulthood, females sometimes remain with their natal group. Females exert dominance over the males of their troop (true for most lemur species), and are known to chase males away from a preferred feeding site. Males, however, are responsible for protecting their troop and defend their group’s territory from rival interlopers. Disputes with outside lemur groups typically occur when territories overlap. But these confrontations are rarely violent. Instead, a lot of posturing occurs. Scent marking, chasing, machismo displays, vocalizations, and “staring contests” are employed.
Home range size—from 19.8 to 37 acres (8–15 ha) depending on habitat quality—is relatively small for eastern lesser bamboo lemurs when compared to home range size for other bamboo lemurs.
Nevertheless, eastern lesser bamboo lemurs only venture out of their home range when food sources are scarce.
Bathroom etiquette is a thing in the jungle, at least with these lemurs. Known as “latrine behavior,” eastern lesser bamboo lemurs stand in queue and take turns defecating in a single, centralized location.
Vocalizations are a key part of communication in the daily lives of eastern lesser bamboo lemurs. Their rich vocal repertoire includes grunts, clicks, low growls, high-pitched screams, screeches, howls, and purrs. Each vocalization conveys a specific message.
Low-intensity alarm calls signify possible danger, whereas high-intensity alarm calls signify imminent danger. Specific alarm calls are used depending on whether the threat is from an aerial or ground predator. Intimidation calls (shrill screams) are intended to scare away outsiders, while contact calls, over short and long distances, identify the location of troop members. Females use mating calls as they enter estrus. When separated from her mother, an infant may emit a high-pitched distress call; when a mother returns to her infant and offers comfort by licking her young one, the infant purrs while the mother emits soft grunts.
Body trembles and teeth grinding may accompany certain vocalizations.
These lemurs also rely on olfactory cues to send and receive important information among troop members and with outsiders. Fortunately, Nature has fitted eastern bamboo lemurs with sweat glands on their forearms and near their armpits that facilitate olfactory communication. Scent marking is performed on a substrate, with papyrus plants being a favorite of the species. Before depositing their pungent secretions, individuals scratch the leaves of the papyrus plant with their teeth. They then either rub the leaves against their scent glands or urinate on the plant. Like adult male ring-tailed lemurs, male eastern lesser bamboo lemurs engage in “stink fights.” During a “stare down” with a rival, an adult male draws his long tail along his forearm to capture the secretions of the scent glands, then waves his stinky, saturated tail over his head to intimidate his rival.
While on the ground, the lemurs may run in circles around a patch of vegetation (“tamping down” the area) to identify their location and claim it as territory. They might chase outsiders away from the area.
Social grooming is the only documented tactile communication for the species. The lemurs engage in this practice to establish bonds with one another.
Females are considered reproductively mature at 2 years of age and come into estrus once a year thereafter; males are considered reproductively mature at 3 years of age. The species is mostly monogamous. Breeding in Ranomafana National Park occurs during the dry season (June and July) with births occurring during the rainy season (October and November) when bamboo, the species’s primary food source, is plentiful. (Overall, the birth season for this species is October through January.) After a 140-day gestation period, a female gives birth to a single infant; twin births are rare. Typical interbirth interval is one year.
A newborn weighs a mere 1.6 oz (45.2 g) and is completely dependent on her mother, who carries the tiny one in her mouth for the first two weeks of her infant’s life. After two weeks of age, the infant is able to cling to her mother as mom goes about her day. Mothers will carry their young in this way for about three months. If he feels like helping, an infant’s father might carry his child during this period. Male bamboo lemurs are reported to offer a bit more support than other lemur species. Parental care, however, largely remains the mother’s responsibility.
At three weeks of age, an infant is able to jump, hop, and walk. She begins eating bamboo by six weeks of age; however, she remains dependent on her mother to forage for her. A mother “parks” her infant on a branch in the middle of a bamboo grove while she goes off to forage. The dense thicket provides camouflage protection from predators. Mothers may return periodically to groom or nurse her infant. By 20 weeks of age, her infant is completely weaned.
Aside from being the unwitting prey of their predators, the specific ecological role of eastern lesser bamboo lemurs has not been widely deliberated. Wildlife biologists know, however, that these primates represent an exclusive population.
Along with all other lemur species, eastern lesser bamboo lemurs are found nowhere in the world outside of Madagascar. Yet they are important global citizens in Nature’s web of life. Scientists recognize Madagascar as host to 21% (14 of 65) of all primate genera and 36% (5 of 14) of all primate families. Of the 113 documented lemur species on the island, 90% are threatened with extinction. Therefore, scientists have identified primate conservation as Madagascar’s “single highest priority.” Eastern lesser bamboo lemurs are intrinsic ambassadors of this urgent conservation effort.
The eastern lesser bamboo lemur is listed as Vulnerable by the International Union for Conservation of Nature (IUCN, 2018), appearing on the IUCN Red List of Threatened Species. Though its conservation status is not as dire as other lemur species, the population is decreasing. Eastern lesser bamboo lemurs are one of the most hunted of all lemurs, and they are frequently kidnapped and kept as pets. Major human disturbances, such as slash and burn agriculture, also negatively impact the species. However, in somewhat of a paradox, certain species of bamboo plants thrive as secondary growth. In these secondary growth forests, eastern lesser bamboo lemurs also appear to thrive, or have the potential to thrive.
Natural predators include boas (Boidae), particularly the Malagasy tree boa (Sanzinia madagascariensis), ring-tailed mongooses (Galidia elegans), fossas (Cryptoprocta ferox), owls (Strigiformes), and Madagascar serpent eagles (Eutriorchis astur). Raptors, dogs, and cats also pose a threat.
The eastern lesser bamboo lemur is listed in Appendix I of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
Ranomafana National Park, home to eastern lesser bamboo lemurs (and to more than 20 other species of lemurs), affords them with a measure of protection through Madagascar’s conservation laws.
SOS Lemurs (or Save Our Species – Lemurs) is a conservation group founded to protect lemur populations and preserve their habitat. The group is currently working on a lemur conservation strategy with the IUCN’s Species Survival Commission. This five-year initiative (2017–2021) is funded by a Geneva-based private foundation.
Initiatives include facilitating community education programs that foster appreciation for Madagascar’s lemurs; establishing livelihood alternatives to help local citizens coexist with the lemurs—instead of hunting them; and supporting local conservation groups and nongovernment organizations (NGOs) to develop and achieve long-term goals for saving lemur species from extinction.
Wildlife biologists have declared lemurs the most threatened mammal group on earth, due to the combined pressures of hunting and habitat loss. They further assert that only a coordinated conservation initiative can save the world’s lemurs from forever vanishing.
Written by Kathleen Downey, March 2020