GRAY-BROWN MOUSE LEMUR

Microcebus griseorufus

Geographic Distribution and Habitat
The gray-brown mouse lemur is a prosimian that is found throughout the Toliara province, which spans much of south and southwestern coastline of Madagascar. Prosimians are the most primitive of the primates, and they all live in the Old World—that is, Africa or Asia. Gray-brown mouse lemurs, like all lemurs, are endemic to the island of Madagascar, off of Africa’s southeast coast. The mouse lemur genus, Microcebus, includes at least 24 species, all of which are closely related. They have very few physical differences, which is why most are named after their color. However, they are genetically diverse.

Gray-brown mouse lemurs live in a variety of forest habitats, including spiny desert, dry arid regions with sporadic rainfall, dry thorn scrub, and gallery forests, the latter of which are stretches of forest that form along the banks of rivers and wetlands. Gray-brown mouse lemurs occupy habitats from low shrub-like vegetation to mid-level canopies. They are found at elevations ranging from sea level to 820 ft (250 m).

Gray-brown mouse lemurs are sympatric with several other species of mouse lemur, meaning they share the same regions of forest. Despite sharing ranging patterns, researchers have not observed any crossbreeding or daily interaction between other species of mouse lemurs and gray-brown mouse lemurs.

Gray-brown mouse lemur range, IUCN 2020

Size, Weight, and Lifespan
As you might suspect from their name, mouse lemurs are very small primates. From head to tail, they measure around just 12.3 cm (4.8 in). They typically weigh between 43.7 and 62.6 g (1.5-2.2 oz). Their weight fluctuates with the seasons and depends upon available food sources. Their small stature makes these weight discrepancies minute. Gendered weight differences are not yet clearly known. 

Appearance
Since mouse lemurs share many physical qualities, they are characterized by their coloring. The gray-brown mouse lemur has alternating light neutral gray, pale neutral gray, and light to medium brownish fur. They typically have a lighter cream color running along their underside, from the belly up to the neck. Their eyes and mouth are surrounded by a lighter variation of the body color and they have a tannish-cream to cinnamon-colored dorsal stripe that starts between the eyes and runs up to the crown of the head. Their large ears are usually lighter than their body coloring. Their hands and feet are colored grayish-white to a light tan, and their whiskers are darker in color.

They have proportionally sized extremities and hands and feet, similar to humans; like other lemur species, they have opposable thumbs. The tail usually measures equal to the length of the body.

Diet
Most species of mouse lemurs are omnivorous. Gray-brown mouse lemurs mostly eat tree gums and saps, but they also consume fruits, nectar, flowers, leaves, insects, and small invertebrates. Their diet is seasonally dependent, meaning it changes seasonally based on changing food sources. Given their wide distribution, their diet can be very regional. For example, gray-brown mouse lemurs who occupy more arid habitats will eat more insects and flowers.

Behavior and Lifestyle
Gray-brown mouse lemurs are nocturnal, meaning they are active during the night and they rest during the day. Their large night-vision eyes and excellent hearing guide them through the dark forest floor and canopy. Their nocturnal schedule gives them an advantage: they are able to rest out of sight when their predators hunt for food during the daytime. Their nocturnal schedule is also vital to their foraging capabilities. Being as small as they are, they could not compete with other small mammals for food during the daylight.

Gray-brown mouse lemurs are a rare example of primates that undergo seasonal torpor when there are fewer resources available. When in this state, both their body temperature and metabolic rate decrease. This allows them to survive periods of reduced food availability. 

During plentiful times, at around dusk, they stir and start out to forage. They spend the rest of the night traveling in search of food. It is believed that—like other species of mouse lemurs—gray-brown mouse lemurs are solitary foragers. While they do sleep with the group at the nesting site, they set out alone to find food.

Fun Facts

Until 1992, there were only two recognized species of mouse lemurs. However, today there are 24 recognized species!

The gray-brown mouse lemur is also known as the reddish-brown mouse lemur.

Mouse lemurs are considered one of the smallest species of primate on the planet. 

Daily Life and Group Dynamics 
The family and group life of gray-brown mouse lemurs has not been extensively studied. However, we do know that they sleep in groups of no larger than 15 individuals, which are comprised of females and their dependent offspring.

Once males reach sexual maturity, they leave the group and begin their search for mates. They continue this cycle throughout their lives, as gray-brown mouse lemurs are not monogamous. Males disperse so that their home range overlaps with several different females. This could suggest that, similar to other species of mouse lemur, such as the gray mouse lemur, females are more dominant than males and have first choice over food preference and mates.

Communication
Being a nocturnal animal often means you rely upon your hearing and auditory senses. It is believed that communication is one way mouse lemur species differentiate themselves. Many species of mouse lemur may look similar and occupy the same range, but their vocal calls and communications are very distinct. These vocal calls are most likely used to determine where young are, find other members of the group, or alert potential danger.

Verbal communication is only one way to communicate. There is also gesture, physical, and nonverbal communication, all of which primates utilize. Small gestures of attention or physical touch are ways that the young communicate with mothers. Vise versa, physical touch or gesture communication, such as staring, are a very important aspect of this small prosimian’s communication methods.

Reproduction and Family
Gray-brown mouse lemurs typically only reproduce during the rainy season, from September through January. There may be exceptions to this, but researchers have only observed mating behavior during those months. Mating behavior is not widely known, but it is believed they display vocal mating calls similar to other mouse lemur species. After successful breeding, a 60-day gestation period follows, which produces one to two offspring.

Little is known about the parenting techniques of this species; however, researchers believe they display similar parenting behaviors to other mouse lemurs. Some of these behaviors may include the practice of allomothering, which is when multiple mothers in a group take care of each others infants. Infants are able to grasp the mother’s belly, but do not ride on her back when moving. Instead, they are carried in the mother’s mouth—their small size and fragile state makes this a much safer and easier way to carry infants.

Ecological Role
Gray-brown mouse lemurs contribute to the high biodiversity of the region. Due to their consumption of flowers and seeds, they are important seed dispersers. Their small size also make them a food source for birds of prey and snakes.

Conservation Status and Threats
Mouse lemurs as a whole are considered to be Endangered. However, some subspecies are more or less endangered than others. The gray-brown mouse lemur has a steady widespread population throughout its range. Because of this, its population size and demographics have not been well researched over the last two decades. The International Union for the Conservation of Nature annual Red List of Threatened Species lists them as Least Concern (IUCN, 2018). It is believed that the population is probably in a slow decline, and faces uncertainty as the landscape of Madagascar continues to be exploited.

Current and future concerns to this species are entirely man-made. All of Madagascar faces deforestation, due in part to charcoal and commercial maize production. Nearly 80% of the country’s original forest has been lost in recent decades. Primary forest only covers 12% of the country’s land. This poses a large threat to nearly all species that live on Madagascar, as 90% of the islands species live in or heavily rely on the forest that remains. In addition to deforestation, a changing climate has the potential to affect these mouse lemurs, and all species living on the island.

Conservation Efforts
While no specific conservation or protective efforts exist solely for the gray-brown mouse lemur, there are many efforts that aim to protect all species of primate that reside on Madagascar. Large organizations such as World Wildlife Fund (WWF) aim to work with local members of communities as well as lawmakers to educate people about the importance of their remaining wildlife and to try and mitigate the damages done by deforestation.

The Lemur Conservation Foundation has a large sanctuary center for many species of lemur and aims to educate the community about all species of lemur. This center combines education, research, and a sanctuary setting to benefit all species of lemur that face danger on the island.

References:

  • http://pin.primate.wisc.edu/factsheets/entry/mouse_lemur/taxon
  • http://neu.rrz.uni-hamburg.de/onTEAM/preview/presse/pressemitteilungen/2015/pm26_e/
  • Don E. Wilson & DeeAnn M. Reeder (editors). 2005. Mammal Species of the World. A Taxonomic and Geographic Reference (3rd ed), Johns Hopkins University Press, 2,142 pp 
  • http://www.iucnredlist.org/details/136637/0
  • https://dukespace.lib.duke.edu/dspace/handle/10161/7291

Written by John DeVreese, August 2018