MADAME BERTHE'S MOUSE LEMUR

Microcebus berthae

Geographic Distribution and Habitat
Sometimes known as the pygmy mouse lemur or Berthe’s mouse lemur, the Madame Berthe’s mouse lemur is named after the conservationist and primatologist Berthe Rakotosamimanana of Madagascar.

This species of lemur is restricted to a small area within the Menabe region in western Madagascar. They live in highly seasonal dry, deciduous forests, in particular the Kirindy Forest. Populations have formerly been found in the nearby Réserve Spéciale d’Andranomena and in the Analabe region, but conservationists fear that the populations in both of these areas may have been wiped out. In the Kirindy Forest, this species is sympatric with the gray mouse lemur (Microcebus murinus).

Madame Berthe's mouse lemur geographic range. Map: IUCN, 2020

Size, Weight, and Lifespan
The Madame Berthe’s mouse lemur is the smallest primate in the world. The average head and body length of adult males is just 4.6 in (11.8 cm), and is 5 in (12.7 cm) for females. Their tails are longer than their bodies and measure approximately 5.1 in (13.0 cm). Their ears measure around 0.7 in (1.7 cm). On average these tiny primates weigh just 1.2 oz (33 g). For perspective, that’s about a third of the weight of a regular-sized apple. Females are sometimes heavier, on average, than males, but males fluctuate in weight and become similar to females in weight when the mating season approaches.

The mouse lemurs have some of the shortest primate lifespans and this species probably only lives around 6–8 years in the wild, although they may live longer in captivity.

Appearance
With their diminutive size, long tails, and large, round eyes perfectly adapted to their nocturnal lifestyles, it is easy to see why these primates are known as “mouse” lemurs. Madame Berthe’s mouse lemurs have short and dense reddish-brown fur that is tinged with orange in places. Their belly and chest are cream-colored and they have a darker-brown stripe running along their backs to their tails. They also have a white stripe extending from their forehead to the tip of their muzzle. They can be distinguished from the closely related gray mouse lemur by their relatively shorter tails and ears.

Photo credit: Allan Hopkins/Flickr/Creative Commons

What Does It Mean?

Deciduous Forest: 
Forests that change seasonally. The word deciduous means to fall off at maturity. The opposite of deciduous is evergreen.

Estrus:
A recurring period of sexual receptivity and fertility in many female mammals.

Slash-and-burn agriculture:
A method of unsustainable farming where farmers clear land by cutting and burning flora in order to create an empty field—a “swidden”—for cultivation. Such practices are detrimental to local ecosystems.

Sympatric: 
Occurring or living in the same area; overlapping in distribution. 

Visit the Glossary for more definitions

Diet
The Madame Berthe’s mouse lemur’s diet is highly specialized; they are omnivorous, but the large majority of their diet is made of sugary secretions produced by the homopteran larvae of the flower bug (Flatida coccinea). They also supplement their diet with arthropods and small vertebrates like geckos and chameleons. Only a very small portion of the diet (around 2%) consists of plant matter, such as fruit and flowers. 

Behavior and Lifestyle
These lemurs are nocturnal, so they are active at night and sleep for most of the day. They tend to sleep in relatively open sites, in naturally occurring tree nests, rather than in tree hollows. During the day they forage alone throughout their home range. Individual’s home ranges tend to overlap with others, but more so for males than females. Females’ home ranges are around 0.01 sq miles (2.5 hectares) and usually overlap with one or two other females, although only about a quarter of the range is shared. Males have larger home ranges, of around 0.02 sq miles (5 hectares), but share their home with, on average, around seven other males. When they forage, these lemurs travel extensively within their home range and usually travel more than 10 times the perimeter of the home range each night.

Fun Facts

The Madame Berthe’s mouse lemur is the smallest primate in the world, weighing just 1.2 oz or 33 g.

They forage alone at night, but often sleep in small groups during the day.

There are usually a higher proportion of females than males in any given area, suggesting that male mating competition is high.

Daily Life and Group Dynamics 
While described as solitary foragers, Madame Berthe’s mouse lemurs often sleep in close proximity to other individuals of both the same and the opposite sex. However, there is a high level of individual variation in how often they sleep alone versus with others, showing individual differences in their level of sociality. Some sleeping groups remain the same over multiple consecutive days and in different sleeping sites. It is currently unclear whether these lemurs choose to sleep in groups to provide protection from predators, to stay warm, or simply because there is a shortage of good sleeping sites in the forest.

These mouse lemurs forage alone during the night and only a small percentage of their active hours are spent interacting with other individuals. Interactions between males and females are most common, although it is fairly common for two or three males to interact with one another at the same time. In general, males tend to interact more than females, and more with females than males, suggesting that they preferentially seek out interactions with females.

Affiliative interactions include huddling and grooming are especially common between nest-mates at both the beginning and end of the nighttime activity, while agonistic interactions can include grabbing, biting, and chasing. These interactions occur both within and between sexes and it seems this species, like other solitary foragers, likely have an elaborate social network that we don’t yet fully understand.

Communication
Like many other nocturnal primates, it is likely that olfaction, through scent-marking, is an important mode of communication. Closely related species of mouse lemurs are known to use both urine washing, where urine is rubbed on the hands and feet and then deposited on the branch, and mouth wiping, where the mouse lemur wipes the corner of the mouth, the face, and the head along a branch to leave a scent to provide information to other lemurs. Other species of mouse lemurs are most often known to engage in scent-marking as they leave their nests for the night.

Mouse lemurs also use vocalizations to communicate. Three main categories of vocalizations have been identified: trills, wide-band zips, and whistle/tsaks. They likely use these vocalizations to signal their location to other mouse lemurs, among other information, although more research is needed to better understand the contexts in which these vocalizations are used.

Reproduction and Family
The high proportion of males to females in a given location means that there is a probably a high level of mating competition in Madame Berthe’s mouse lemurs. Males also travel further than females and expand their home ranges during mating season, suggesting that their mating system is probably characterized by “scramble competition,” where males compete to locate females who are in estrous. Additionally, species that live in social systems where male mating competition is high generally have larger testicular volume compared to body size, and Madame Berthe’s mouse lemurs have the largest testicle-to-body-size ratio of all primates.

It is unlikely that males play a role in offspring care and offspring likely stay with their mother until they are sexually mature, at approximately 10 months of age. Both sexes will then leave their mother to form their own home range. More research is needed to understand whether or not females stay in home ranges close to their mothers’.

Photo credit: FC Casuario/Creative Commons

Ecological Role
Given that Madame Berthe’s mouse lemurs eat very little plant material, their role in seed dispersal is likely to be much less than in other primates. Their primary ecological impact is probably linked to the insects whose secretions they depend on.

Conservation Status and Threats
​​The International Union for Conservation of Nature lists the Madame Berthe’s mouse lemur as Critically Endangered (IUCN, 2019), appearing on the IUCN’s Red List of Threatened Species. Given that they are restricted to such a small area, any habitat degradation can have severe consequences for their remaining population. Unfortunately, their habitat is currently under threat from slash-and-burn agriculture, the harvesting of trees for charcoal production, and illegal logging.

Conservation Efforts
Madame Berthe’s mouse lemurs are listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), meaning that their trade is banned. The Kirindy Forest has recently been included in a protected area that provides official protection to this species. However, this protection is not sufficiently enforced and deforestation is ongoing in this area.

An education and awareness program with the Madame Berthe’s mouse lemur as its flagship species was recently initiated and is conducted with children and youth of surrounding communities at the Kirindy Forest. In the past few years, more forest patrols have also been started in the remaining forest fragments.

However, more actions are needed, along with more research into distribution and abundance, in order to prevent this species from going extinct.

​References:

  • Atsalis S, Schmid J, Kappeler PM (1996). Metrical comparisons of three species of mouse lemur. Journal of Human Evolution, 31(1), 61-68.
  • Dammhahn, M., & Kappeler, P. M. (2008). Comparative feeding ecology of sympatric Microcebus berthae and M. murinus. International Journal of Primatology29(6), 1567.
  • Dammhahn, M., & Kappeler, P. M. (2005). Social system of Microcebus berthae, the world’s smallest primate. International Journal of Primatology, 26(2), 407-435.
  • Dammhahn, M., & Kappeler, P. M. (2008). Small-scale coexistence of two mouse lemur species (Microcebus berthae and M. murinus) within a homogeneous competitive environment. Oecologia, 157(3), 473-483.
  • Jolly, C. J., & Phillips-Conroy, J. E. (2003). Testicular size, mating system, and maturation schedules in wild anubis and hamadryas baboons. International Journal of Primatology, 24(1), 125-142.
  • Alltheworldsprimates.org
  • https://www.iucnredlist.org/species/41573/115579496

Written by Jennifer Botting, PhD, January 2021