Madame Berthe’s mouse lemur, Microcebus berthae
MADAME BERTHE'S MOUSE LEMUR
Microcebus berthae
Geographic Distribution and Habitat
Madame Berthe’s mouse lemurs (Microcebus berthae), also known as Berthe’s mouse lemurs, are the world’s smallest primate species. They are endemic to the Menabe-Antimena Protected Area in the Menabe region, western Madagascar.
The geographic distribution of this tiny, critically endangered species includes the dry, deciduous forests of Kirindy and Ambadira. It covers an estimated area of 53.7-134 mi² (139.2-348 km²) and has an elevation range of 0-492 feet (0-150 m).
The Menabe region that Madame Berthe’s mouse lemur calls home contains one of Madagascar’s largest remaining swaths of dry deciduous forest. In the dry season, between April and November, the average monthly rainfall is just 3.93 inches (10 cm). During the rainy months from December to March, the region receives an average rainfall of 27.5 inches (70 cm) each month. It reaches its highest annual temperature of 87.2°F (30.7°C) during the wet season, and the lowest annual temperature of 66.2°F (19°C) during the dry season.
This species is very vulnerable to habitat disturbance and appears significantly less in habitats that are degraded. In 2019, one subpopulation of Madame Berthe’s mouse lemurs within the Kirindy forest unfortunately declined to zero individuals.
Madame Berthe’s mouse lemur is sympatric with the gray mouse lemur (Microcebus murinus), meaning they are closely related species that live in the same geographic area. Although the two species have a great deal of overlap in the food they eat and the habitat they prefer, Madame Berthe’s mouse lemur and the gray mouse lemur are not known to compete with each other directly.
The island of Madagascar is home to more than 100 lemur species, though most are classified as endangered or critically endangered due to habitat loss.
Size, Weight, and Lifespan
Madame Berthe’s mouse lemur is as tiny as, well, a mouse! Coming in at an average weight of 1 ounce (31 g) and a body length of 3.5-3.7 inches (9-9.5 cm), this is the tiniest primate species in the world. Their tails are often longer than their bodies, adding 5.1-5.5 inches (13-14 cm) of length.
They are not sexually dimorphic—that is, males and females are rather similar in both size and appearance. They can fluctuate greatly in size, however, with males becoming larger than females during the breeding season. At all other times of the year, the female is larger.
Data on the lifespan of Madame Berthe’s mouse lemur is limited. Under rare, highly managed captive conditions—such as in well-resourced, professionally run institutions—other mouse lemur species have lived to 18 years.
Appearance
Madame Berthe’s mouse lemurs are mostly reddish-brown, a shade known as rufous, similar to rusty iron. A well-defined stripe slightly darker in color runs from just behind the shoulders to the tip of the tail. On their belly and the underside of the limbs, the fur can be cream-white, light yellow-brown, or pale gray. The fur on their hands and feet is a dull beige. All these colorings work together to help these lemurs hide from predators by breaking up their silhouette and blending into their surroundings.
The fur on their head is more brightly colored than the rest of their body. They have very short ears, a dull white patch above the nose, and narrow black bands around their big, round eyes. Yes, those eyes are cute, but they also serve a very important purpose–letting in lots of light to help this nocturnal species see at night!
Like other lemurs, Madame Berthe’s mouse lemur’s six front lower teeth are grouped in a “toothcomb” arrangement that’s handy for running through their fur to help them stay clean and also helps them scoop sap off of tree trunks.
Diet
Madame Berthe’s mouse lemur primarily eats sugary excretions from sap-eating insects and animal matter, including arthropods and small vertebrates. Some supplements to their diet include fruits and tree gums, which overlap with the diet of other mouse lemur species. Unlike these other lemurs, however, Madame Berthe’s mouse lemur mostly eats the same food throughout the year, with little variation from season to season.
Although this species lives in groups, they do most things, including foraging for food, alone.
Behavior and Lifestyle
Madame Berthe’s mouse lemurs are nocturnal, so they are active at night and sleep during the day. As arboreal primates, they spend most of their time up in the trees and prefer to sleep in tangles of thin branches surrounded by leaves. They may also choose to hunker down in tree holes or the old nests of giant mouse lemurs. Whatever the site is made of, they are typically found 16-39 feet (5-12 m) off the ground.
This species sleeps and forages alone, likely because a group would be too visible to predators. The only exception is a mother and her young. Females tend to reuse the same sleeping site, while males distribute their sleeping sites over a larger area.
Mouse lemurs are quadrupeds and use all four limbs to run and leap short distances. Though Madame Berthe’s mouse lemurs mostly spend time on tree branches, they can also occasionally be found on the ground.
Both male and female Madame Berthe’s mouse lemurs have daily periods of torpor: a state when their metabolism, body temperature, and activity levels all drop. This helps them save energy. Some other species of mouse lemurs experience seasonal periods of torpor to help them get through moments of resource scarcity, but this is not the case with Madame Berthe’s mouse lemurs.
When Madame Berthe’s mouse lemur was first discovered in the Kirindy forest in 1992, scientists first thought it was the pygmy mouse lemur (Microcebus myoxinus). The species is named after Berthe Rakotosamimanana, a conservationist and primatologist from Madagascar.
Madame Berthe’s mouse lemur has an estimated population density of 30-100 individuals per ~0.4 square mile (1 square km). Males have an average home range of 12 acres (4.9 ha), which is much larger than the 6.2-acre (2.5 ha) home range that females normally keep.
Although this species, like other mouse lemurs, lives in groups with multiple males and females, there is not much interaction between individuals. In fact, scientists observed them come near each other an average of 3.2 times for every 100 hours of observation. Madame Berthe’s mouse lemur prefers to sleep alone and forage alone.
Madame Berthe’s mouse lemur, like many other nocturnal primates, relies heavily on scent to communicate. Other mouse lemur species urinate on their hands and feet, a practice known as urine-washing, so that they can leave a scent to inform other lemurs about their identity and movements. In these other mouse lemur species, this scent-marking frequently occurs as they leave their nests for the night.
Studies of mouse lemurs in captivity found that scent-marking was useful for identifying individuals, finding mates, conveying alarm, and marking their territory.
Mouse lemurs are also very vocal and can emit 7-8 different types of calls. Predator-avoidance whistle calls and reproductive calls vary greatly between species. And although this is true for mouse lemurs as a group, no studies of communication in Madame Berthe’s mouse lemur have been conducted.
Although the mating system of any mouse lemur remains mostly unknown, scientists are reasonably sure that they are promiscuous and competitive, meaning each mouse lemur has multiple partners and the males often fight for access to females. There is certainly evidence that this is the case for Madame Berthe’s mouse lemurs, from the large testes size for males to the presence of sperm plugs in the females’ vaginas.
Breeding seasons vary for mouse lemur species and are unknown for Madame Berthe’s mouse lemurs. For both sexes, the genitals undergo visible changes during this season. Males’ testes may swell 5-10 times their regular size, while the female’s vagina, normally closed, opens only when she is giving birth or in estrus (fertile and willing to mate). The fact that males travel further than females and have larger home ranges during the mating season also suggests that they engage in “scramble competition,” where males compete with each other to find females to mate with.
Studies of other mouse lemur species in captivity found that mothers nurse and carry infants in their mouths until they are 6 weeks old. These young ones open their eyes a few days after birth, begin playing at 10 days, leap at 3 weeks, and become independent by two months of age.
Based on limited observations of Madame Berthe’s mouse lemurs in the wild, it is believed that males leave their home range once they are sexually mature, while females remain in the same area for life.
Madame Berthe’s mouse lemurs are an essential part of the food web in their environment. Because they are specially adapted to digest tree gums, they play the important ecological role of cycling these nutrients back into the ecosystem. By eating plant matter such as fruits, Madame Berthe’s mouse lemurs also contribute to the growth and diversity of plant life in their environment through seed dispersal. Additionally, Madame Berthe’s mouse lemurs are particularly susceptible to predation by fossas, snakes, and raptors.
The International Union for Conservation of Nature lists Madame Berthe’s mouse lemur as Critically Endangered (IUCN, 2022), appearing on the IUCN Red List of Threatened Species. The species is primarily threatened by habitat loss and degradation caused by slash-and-burn agriculture, illegal logging, and the harvesting of trees for charcoal production.
These threats are not under control; ongoing slash-and-burn agriculture for maize and peanuts continues to threaten the forest fragments remaining in the Menabe region. Additionally, the effects of past deforestation may not be reversible. As these habitats degrade, the geographic range of Madame Berthe’s mouse lemur continues to shrink.
Although Madame Berthe’s mouse lemur was historically found in the Analabe Private Reserve, that is no longer the case, as there are no longer any forest habitats there to sustain the species. A sub-population of the species that scientists had been tracking for over a decade in the Kirindy forest declined to zero individuals in 2019. Based on the continuing decline in habitat quality and area occupied by Madame Berthe’s mouse lemur, scientists estimate the species’ limited population will experience more than an 80% decline over the next 10-17 years.
Madame Berthe’s mouse 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. As a species listed in Appendix I, it cannot be traded for commercial purposes. As of 2022, no Madame Berthe’s mouse lemurs are being kept in captivity.
Although over 74,000 acres (30,000 ha) of protected lands, established in 2015, encompass the Kirindy and Ambadira Forests that Madame Berthe’s mouse lemur has traditionally called home, there is no effective law enforcement of these protections. Even as the region is recognized as an important conservation zone, an additional 30% of the remaining forest habitat has been destroyed by slash-and-burn practices.
Advocacy groups have created an education and awareness program for children and youth in the surrounding communities, using Madame Berthe’s mouse lemur as a flagship species. More intensive patrolling beginning in 2018 in the Kirindy Forest seems to have also contributed to a slight decrease in the rate of deforestation.
- https://www.iucnredlist.org/species/41573/215090010
- https://www.alltheworldsprimates.org/
- https://www.gbif.org/species/4266980
- https://primate.wisc.edu/primate-info-net/pin-factsheets/pin-factsheet-mouse-lemur/
- https://link.springer.com/article/10.1007/s10764-008-9312-3
- https://pmc.ncbi.nlm.nih.gov/articles/PMC2515545/
- https://link.springer.com/article/10.1007/s10764-005-2931-z
- https://link.springer.com/article/10.1023/B:IJOP.0000019154.17401.90
- https://news.mongabay.com/2022/09/worlds-smallest-primate-is-fading-into-extinction-scientists-fear/
Written by Jiayu Liang, May 2026