GRAY MOUSE LEMUR

Microcebus murinus

Geographic Distribution and Habitat
The gray mouse lemur, also known as the lesser mouse lemur, is endemic to Madagascar. They mainly occupy dry deciduous forests from Mahajanga in the northwest to Tulear in the southwest, along most of the west coast. A distinct population has also been found in the southeast near Fort Dulphin.

The gray mouse lemur is one of the most adaptable lemur species; they are able to live in a variety habitats. Not only can they survive in dry habitats, but they also thrive in lowland tropical forests, scrub forests, gallery forests, secondary forests, plantations, and degraded habitats. Gray mouse lemurs are arboreal and stay high on tree branches. However, they will occasionally descent to the ground level to forage.

Gray mouse lemur range, IUCN 2020

Size, Weight, and Lifespan
The gray mouse lemur is one of the smallest living primates. In fact, they were once thought to be the smallest living primate, but this was disproved when the pygmy mouse lemur (Microcebus myoxinus), previously thought to be extinct, was rediscovered. Although gray mouse lemurs are very small, they are the largest of the mouse lemur species. Their head and body length ranges from 4.72 to 5.5 in (12-14 cm). Their tail length measures from 5.1 to 5.9 in (13-15 cm). Mouse lemurs are very light primates, weighing from 1.4 oz to 2.5 oz (40-70 g). They can live between 10-15 years. In captivity, however, they tend to live up to 14 or 15 years.

Appearance
As the name suggests, the gray mouse lemur has a somewhat mouse-like appearance. They have grayish-brown bodies with reddish tones, and a round brownish head with two large projecting ears. The underparts of these lemurs are beige colored and between their two large eyes lies a small white patch of fur. Sometimes individuals have dark markings around their eyes.

Gray mouse lemurs have long tails, which can sometimes be longer than their bodies. They have short limbs. This species shows no signs of sexual dimorphism, which means that males and females are difficult to distinguish from one another. Behind the retina of their large eyes is a layer called the “tapetum” that reflects light. This makes it easier for them to see in darkness. It also makes it easy to spot them in the middle of the night, if one were to shine a light in their direction.

Gray mouse lemurs (as well as other lemur species, tarsiers, and lorises) are prosimians, meaning that they are the “most primitive” of the living primates. Prosimians are primarily tree-dwellers. Their facial features differ from monkeys and apes; they have a longer snout and their noses are usually moist, indicating a great sense of smell. Mouse lemurs’ eyes are large and well-adapted for night vision. Their hands and feet are capable of grasping tree branches. A unique feature of prosimians is that they usually have one long claw on their hindfoot, which is used for grooming purposes. Their other digits (on both hands and feet) have flattened nails instead of curved claws. Gray mouse lemurs have unique teeth, similar to other prosimians. Their long and thin lower incisors and canines are ideal for grooming and scraping gum off trees. Their lower front teeth lie horizontally and protrude, somewhat resembling a brushing comb. These teeth are often called a dental comb because of this.

What Does It Mean?

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

Torpor:
A sleep-like state in which the body decreases physiological activity. 

Visit the Glossary for more definitions

Diet
Gray mouse lemurs are nocturnal primates, who forage for food at night. They are solitary foragers who primarily eat fruit. Flower nectar and pollen, green vegetal matter, beetles, and chameleon are also on their menu. Other insects eaten include moths, crickets and cockroaches, praying mantids, large spiders, Flugorid bugs, and the larvae of Phromnia. During the dry season, gums are an important resource for some populations.

Mouse lemurs concentrate on the base of flowers, ignoring petals. They feed on sap by chewing on fine branches or by scraping using the tooth comb. In the latter case, small insects may be consumed simultaneous with sap. 

Behavior and Lifestyle
The gray mouse lemur has several modes of locomotion. They often travel quadrupedally through the forest. They move along horizontal, vertical, and inclined supports, such as branches and tree trunks. Mouse lemurs can leap up to 10 feet (3 meters) in order catch insects or move to another tree in pursuit of finding food. The individual launches him or herself rapidly outward and grasps tree branches with all four of their limbs (occasionally they grasp the branch firmly with just their hind limbs). Sometimes they will come close to the ground for feeding. In this case, they use a different type of locomotion that looks similar to hopping in a frog-like fashion.

Gray mouse lemurs sleep in tree holes, nests of dead leaves, or dense vegetation during the day, often with up to 15 other individuals. Each mouse lemur may use between 3 and 9 different tree holes or nests, occupying the same nest for several consecutive days. Males usually sleep alone, but during breeding season they sometimes share a nest with a female.

In order to save energy during times of inactivity, the gray mouse lemur enters into a period of “torpor.” This takes place mainly in the cooler dry seasons. When in this state, both their body temperature and metabolic rate decrease. This allows them to survive periods of reduced food availability. During the wet season, gray mouse lemurs are more active due to higher temperatures and an increase in food supply. They will also breed during this time.

Activity levels may differ between populations. Some populations do not enter seasonal torpor; other females may be completely inactive and stay dormant in their nests for up to five months. Males on the other hand rarely stay inactive for more than a few days, and will become fully active again before the females.

Fun Facts

Mouse lemurs store fat in their tails and hind limbs when food is scarce and may store up to 35 percent of their body weight. 

Sometimes gray mouse lemurs are spotted in roadside brush and gardens.

Daily Life and Group Dynamics 
The social organization of gray mouse lemurs is quite complex, consisting of a multi-male/multi-female system. Females are considered to be dominant over males, giving them preferential access to resources and the choice of whom they mate with. This is a unique characteristic since female dominance is rare in prosimians. Each individual gray mouse lemur occupies a small home range. Ranges of all group members tend to overlap in a medial area. Males have larger home ranges than females, and this increases during mating season. Males roam widely, almost quadrupling their habitual home range. 

During the day, related females form sleeping groups. If there are no available female kin, females then sleep alone. Males only occasionally share sleeping sites. Since these primates are nocturnal, they sleep and stay in their nests during most of the day. Mouse lemurs are often found living sympatrically with other primates. In a given habitat, more than one species of mouse lemur can be found. The gray mouse lemur has been found to coincide with the golden-brown mouse lemur in the northwest and south, and with Madame Berthe’s mouse lemur and the pygmy mouse lemur in the west.

Communication
Communication is important for group coordination and group spacing in gray mouse lemurs, and gray mouse lemurs have a number of different vocal calls. In times of anguish, a distress call is often used by infants when the mother is in contact or away from the nest. This call is a high pitched, piercing sound. When more relaxed, infants emit a purring sound, almost like a cat. Adults also use this call while allogrooming.

A series of alarm calls are emitted by adults in response to disturbances. This is a series of rapid and short whistles, often cryptic in nature so as not to reveal the location of the caller. Other whistle calls include a clear whistle sound used by subordinate adults, especially when inhibiting aggression. A long whistle sound is emitted when there are high levels of disturbance. An intermediate whistle (also known as the “distance communication call”) call is given by adults at dusk, which may function as a spacing call.

Similar to the alarm call, a threat call is also used when there are disturbances or nearby danger. However, threat calls incorporate more growling sounds and sharp barking. While using this call, individuals’ ears will change position into a more horned-ear appearance.

During breeding season, a powerful trill call is emitted by the male. This trill call is used prior to mating when a female in estrus is nearby, as well as during mating. It is also known as the mating call. Another form of the trill call is used by subordinate males and mothers. This trill call is much softer than the mating call and is used as the adult contact call. The softer version of the trill call was found to differ between two different sub-populations of gray mouse lemur by Hafen et al (1998). This suggests a strong possibility that gray mouse lemurs may develop their own dialects in their vocal communication.

Gray mouse lemurs also use gathering calls. These are harmonic calls given by adults around dawn. In addition, tactile communication is used with kin. Often, gray mouse lemurs huddle and groom each other at the beginning and the end of each night.

Reproduction and Family
Between September and March, gray mouse lemurs have the opportunity to mate. They are polgynous, meaning one male often mates with multiple females. When an individual turns one year old they are considered to be fully mature, and thus reproduce during the first year of their lives. Females often give birth to twins. Before the birth of the infants, the mother becomes restless and engages in short periods of self grooming and nesting behavior. After about 45-60 minutes the mother gives birth. She then bites the umbilical cords and cleans the infants. The infants begin to suckle after about 12 minutes. For the first three weeks of their lives, they remain in the nest. The mother only leaves her nest to feed, drink, urinate, or defecate. The mother takes care of the infants by feeding them milk and grooming them.

Photo credit: Charlesjsharp/Creative Commons

Ecological Role
Mouse lemurs have an important relationship with the baobab tree (Adansonia). Baobab tree species are located in arid areas of Africa, Madagascar, and Australia. Some of these trees are known to be at least 2,000 years old and can have a trunk diameter up to 40 feet wide. These massive and magnificent trees are known as the “tree of life.”

Baobab trees provide many resources, such as food, water, and shelter. Two of the main species found living on Madagascar baobab trees are hawk moths and mouse lemurs, which both pollinate the trees. Mouse lemurs emerge after hibernation to feast on the nectar from the baobab tree’s flowers. Hawk moths also feed on the nectar and scatter the tree’s pollen. Mouse lemurs, however, will catch and eat the feeding moths. By catching and eating the moths on the flowers and eating the flowers too, the baobab tree is able to be pollinated forming a mutually beneficial relationship between the tree and the mouse lemur. This allows the baobab tree to thrive!

The low-eared owl, barn owl, several species of snakes, ring-tailed mongoose, and the fossa are the top predators of the gray mouse lemur. In some areas, many domestic dogs prey on these lemurs.

Rural african road among baobab trees. Madagascar.

Conservation Status and Threats
The gray mouse lemur is considered Least Concern (IUCN, 2020) by the International Union for Conservation of Nature Red List of Threatened Species. However, it is likely that this species is in decline due to habitat loss and live capture by humans. In the west of the gray mouse lemur range, there is much habitat loss due to slash and burn agriculture and cattle grazing. Other parts of their habitat are completely destroyed. They often inhabit secondary forests and degraded habitats, but it has been reported that the decrease in habitat quality has unfavorable effects on population dynamics. There is also evidence for increased stress in this species due to poor habitat quality. Gray mouse lemurs in these habitats are less able to participate in periods of torpor in order to save energy, which may lead to higher levels of mortality. In addition, the northern and southern parts of their range have high incidences of live capture for local pet trades. There are also incidences of capture for medical purposes, since medical research still uses a small number of this species.

The geographical range of the gray mouse lemur is extensive and, despite habitat loss, they are still widespread and adaptable. Even though this species is highly adaptable to different types of habitats, they are still very much negatively effected by habitat loss and live capture. 

​Conservation Efforts
This species is listed on the Convention on International Trade in Endangered Species (CITES) Appendix I. The gray mouse lemur is present in eight national parks across Madagascar such as: Andohahela, Ankarafantsika, Baie de Baly, Isalo, Tsingy de Namoroka, Vohibasia, Kirindy Mitea, and Zombitse. They are also present in five reserves: Andranomena, Bemarivo, Beza-Mahafaly, Kasijy, and Maningoza. Gray mouse lemurs occupy several other protected forests in Madagascar and Kirindy Classified Forest. They are maintained in several captive groups in Europe and the United States, including the international studbook by Duke University Primate Center. 

References:

  • http://www.theprimata.com/murinus_reproduction/
  • http://pin.primate.wisc.edu/factsheets/entry/mouse_lemur/behav
  • http://www.theprimata.com/murinus_locomotion/
  • http://www.theprimata.com/murinus_voc_comm/
  • https://www.arkive.org/grey-mouse-lemur/microcebus-murinus/
  • https://animaldiversity.org/accounts/Microcebus_murinus/
  • https://homeguides.sfgate.com/description-flowers-baobab-tree-pollinated-104711/
  • http://science.jrank.org/pages/5517/Prosimians/
  • https://www.nationalgeographic.com/animals/mammals/group/mouse-lemurs/
  • ​https://lemur.duke.edu/discover/meet-the-lemurs/grey-mouse-lemur/
  • http://www.iucnredlist.org/details/13323/0
  • Hafen T, Neveu H, Rumpler Y, Wilden I, Zimmermann E (1998). Acoustically dimorphic advertisement calls separate morphologically and genetically homogenous populations of the grey mouse lemur (Microcebus murinus). 

Written by Tara Covert, August 2018