Mouse Lemurs: Tiny and Endangered Primates of Madagascar
What Are Mouse Lemurs?
Mouse lemurs are tiny and intriguing primates that are native to Madagascar. They have a maximum head and body length of 5.5 inches and a total length (including the tail) of less than 11 inches. They are nocturnal animals and spend the day sleeping in tree hollows or in nests made of leaves. Like many animals that are active at night, they have huge eyes, which face forward.
Mouse lemurs are primates, like other lemurs, monkeys, gibbons, apes, and humans. Although lemurs are considered to be the most primitive primates, they are fascinating animals. Their name comes from the Latin word "lemures", which means "ghost". The name was probably chosen because many lemurs are active in the dark and their large, reflective eyes often look eerie in the faint nighttime illumination.
Mouse lemurs belong to the genus Microcebus. The number of species is uncertain and is increasing as more animals are discovered and studied. Unfortunately, many of the species are endangered because of habitat destruction in their native forests. In addition, they are captured illegally to become exotic pets, since many people find their tiny size and big eyes very appealing.
Mouse lemurs are mammals and belong to the class Mammalia, like us. In addition, they belong to the order known as Primates, as we do. We belong to the family Hominidae while mouse lemurs belong to the family Cheirogaleidae, however. Dwarf lemurs also belong to this family. The bigger lemurs belong to different families.
In addition to having a small body, mouse lemurs have short limbs, bare fingers and toes that aren’t covered by fur, and a relatively long tail. Their enlarged eyes help them to see as they search for food in dim light.
The eyes of a mouse lemur have a light-reflecting layer called the tapetum lucidum (or simply the tapetum) immediately behind the retina. The retina is the light-sensitive layer at the back of the eyeball. When light hits the animal's retina, some of the light passes through it, hits the tapetum behind the retina, and then bounces back through the retina again. This means that light-sensitive cells are stimulated twice, giving the animal better night vision.
When we shine light on a mouse lemur at night, the light reflecting off the tapetum makes the animal's eyes glow. The phenomenon is known as eyeshine. Many other nocturnal animals exhibit eyeshine.
Daily Life and Communication
Mouse lemurs are arboreal and spend most of their lives in the trees. They are generally omnivorous, eating both plant parts and other animals, such as insects. Although they often forage alone, they spend some time in groups and may sleep together in their nests. A group is led by a female.
The animals make a variety of vocalizations, including whistles, trills, chirps, and squeaks. Researchers have discovered that the grey mouse lemur also makes high frequency ultrasonic sounds that are beyond the range of human hearing.
Mouse lemurs emit sounds to coordinate the behavior of their group, to advertise their reproductive state or the presence of a predator, and to attract mates. The animals also release fluids that contain scents in order to mark areas and communicate with other animals. These fluids include urine, feces, saliva, and fluid from the reproductive tract.
The smallest species of mouse lemur is the Madame Berthe’s mouse lemur (Microcebus berthae), which is also believed to be the smallest primate in the world. The minute animal has an average body length of 3.6 inches (not including the tail) and an average weight of only 1.1 ounces.
Madame Berthe's Mouse Lemur
The Madame Berthe’s mouse lemur is named after Madame Berthe Rakotosamimanana, who was a Madagascan conservationist. She lived from 1938 to 2005 and was a highly respected primatologist, teacher, and researcher as well as a conservationist. The little creature named in her honour has reddish-brown fur. Like all mouse lemurs, it has a vertical white stripe between its eyes.
The Berthe's mouse lemur lives in lowland deciduous forests and spends most of its time in the tree canopy. It generally forages alone. Like its relatives, it's an omnivorous feeder and eats fruits, insects, geckoes, and chameleons. It's main food source is the honeydew produced by insects called planthoppers, however. The insects feed on plant sap and then release a sweet liquid—the honeydew—from their anus. The drops of liquid fall onto leaves and stems. The mouse lemurs lick up the honeydew. Planthoppers live in large colonies and produce a lot of honeydew.
In the cooler and drier winter season (which lasts from April or May to September or October), the Berthe's mouse lemur spends part of each day resting in a safe place with a lowered temperature and a decreased metabolic rate. This condition is known as torpor. During periods of torpor, the animal uses less water than normal and conserves energy.
The Madame Berthe's mouse lemur is restricted to an area in the southwestern part of Madagascar and is endangered due to habitat loss. The population is fragmented and is decreasing in size.
The Pygmy Mouse Lemur
The pygmy mouse lemur (Microcebus myoxinus) is considered by most researchers to be the second smallest type of mouse lemur. It's sometimes called the smallest one, however. It's also known as the Peters' mouse lemur.
The animal's fur is red-brown, like that of the Madame Berthe's species. Different species of mouse lemurs look very similar to each other, but careful observations and genetic tests have shown that there are important differences between the species. Not much is known about the biology of Microcebus myoxinus. It seems to prefer sleeping alone in leaf nests and among tangled vines instead of in tree holes.
The animal's population is classified in the "Vulnerable" category of the IUCN's Red List. The IUCN or International Union for Conservation of Nature uses its Red List to classify animals according to their nearness to extinction.
Grey (or Gray) Mouse Lemur
The grey mouse lemur (Microcebus murinus) is the largest member of its group, although it’s still a very small primate. Unlike the Madame Berthe’s species, it’s not endangered. In fact, its population is classified in the “Least Concern” category by the IUCN. It has grey or brownish-grey fur. At one time, all mouse lemurs were thought to be different forms of this animal.
Like its relatives, Microcebus murinus is fast and agile while it's exploring the tree canopy. It searches for food on its own but shares a hole in a tree with other mouse lemurs during the day. It eats mainly insects, fruits, flowers, leaves, and nectar. It also eats small reptiles, gum from injured trees, and honeydew.
Before the dry winter season begins, fat collects in the animal’s tail and hind legs to help keep it alive during its winter torpor. The torpor may last for just a few hours each day. In some colder locations, however, the species has been found to stay in a state of torpor for several days or even throughout the winter.
The animal lives mainly in the western and southern parts of Madagascar and has a much wider distribution than the Madame Berthe’s species. It’s estimated that a quarter of the population is killed by predators every year, but the grey mouse lemur is able to replace its lost population. It's an adaptable animal and seems to have a resilience that many of its relatives lack. Some people worry that since its habitat is being destroyed in certain areas, its numbers may eventually start to decline.
The evidence obtained so far indicates that mouse lemurs have multiple reproductive partners and that a female is only receptive to males for a few hours on a particular day in her cycle. She mates with several males during this short time period. The female often rebuffs the first advances of a male before she will let him mate with her.
The gestation period is around two to two-and-a-half months. The grey mouse lemur typically has twins. At around three weeks of age, the babies leave the nest for the first time. If they need to be moved away from the nest area, the mother carries the youngsters around with her mouth instead of letting them ride on her back. The babies are weaned at about six weeks of age and are ready to live independently when they are about two months old.
In captivity, mouse lemurs live for about twelve years. Their lifespan is probably much shorter in the wild. The animals are eaten by many other creatures, including owls, snakes, mongooses, and civets.
Mouse Lemurs and Alzheimer's Disease
In old age, mouse lemurs sometimes develop a condition that closely resembles Alzheimer's disease in humans. Duke University scientists are studying the animals in the hope of helping people. They say that the research is non-invasive and that the animals aren't harmed in the research.
Mice are often used in experiments related to humans. As a scientist says in the video below, mouse lemurs are a much closer match for humans because they are primates like us. The scientists are looking at brain scans of healthy and diseased animals and are studying their genes. They believe that there is something special about the primate body that makes it susceptible to Alzheimer's disease and perhaps certain other neurological disorders.
It's hoped that new drugs will be created to help Alzheimer's. Once the safety of these drugs is demonstrated, the scientists hope to test them on mouse lemurs with neurological problems. Since the animals grow old much faster than humans, studying them could significantly speed up the process of finding a cure for Alzheimer's in people.
Population and Conservation
Madagascar is a small island nation that is dwarfed by the neighbouring continent of Africa. Despite its relatively small size—about twice the area of Arizona—Madagascar has a huge variety of wildlife. Many animals that live there, including mouse lemurs, are found nowhere else on Earth. A difficult but very important task is to balance the needs of the Madagascan people with the needs of the local wildlife so that the amazing biodiversity of the island is maintained.
Many mouse lemur species are threatened by logging, slash and burn agriculture, farming, and mining. The habitat in the areas where the animals live is sometimes destroyed or damaged. Populations may become isolated in fragmented sections of their habitat, inhibiting efficient mating and mixing of genes. Wild predators are a natural part of any ecosystem, but in Madagascar domestic dogs and cats are additional predators.
Conservation organizations are trying to protect mouse lemurs and other wildlife in Madagascar. The animals are protected in the island's national parks. Hopefully the efforts of conservationists will succeed before Earth loses the fascinating creatures that exist on the island today.
Questions & Answers
© 2011 Linda Crampton