Common brown lemurs have short, dense fur that is primarily brown or grey-brown in color. The face, muzzle and crown are dark grey or black with paler eyebrow patches, and the eyes are orange-red. Their tails are long and furry. Common brown lemurs have binocular vision. They have a scent gland that is located at their wrist. The animals use it to leave scent marks in order to communicate with each other.
Common brown lemurs live in western Madagascar north of the Betsiboka River and eastern Madagascar between the Mangoro River and Tsaratanana, as well as in inland Madagascar connecting the eastern and western ranges. They also live on the island of Mayotte. Common brown lemurs inhabit lowland rainforests, montane rainforests, moist evergreen forests, and dry deciduous forests.
Common brown lemurs spend most of their time in upper layers of the forest and only some of their time is spent on the ground. They live in groups of 5-12, but group size can be larger, especially on Mayotte. Groups include members of both sexes, including juveniles, and there are no discernible dominance hierarchies. Common brown lemurs are primarily active during the day, but can be cathemeral (active both day and night throughout the year) and continue into the night, especially during full moons and during the dry season. In the western part of their range, Common brown lemurs overlap that of the Mongoose lemur, and the two species sometimes travel together. In the areas of overlap, the two species also adapt their activity patterns to avoid conflict. To maintain social bonds Common brown lemurs often groom each other. These animals communicate using scent glands and sounds. The sound 'ohn' is used to maintain group cohesion. A 'cree' or high pitched sound individuals use as a territorial call, and the 'Crou' sound is usually the alarm call.
Common brown lemurs are herbivorous (frugivorous, folivorous) creatures. Their diet consists primarily of fruits, young leaves, and flowers. In some locations they may eat invertebrates, such as cicadas, spiders and millipedes. They also eats bark, sap, soil and red clay.
Little is known about the mating system in Common brown lemurs. The breeding season for these animals lasts in May and June. Infants are born in September and October after a gestation period that lasts around 120 days. Females usually give birth to a single baby, but twins have also been reported. During the first three weeks after birth, infants hang onto the mother's bellies. After that, they ride on their mother's backs and later they begin to make their first steps. Infants are usually weaned after 4 or 5 months. Males in this species reach reproductive maturity at around 18 months, and females are ready to breed at 2 years of age.
Main threats to Common brown lemurs include habitat destruction, charcoal production, and illegal logging. Hunting is becoming another serious threat to these animals. They suffer from blowpipes, firearms, bow-and-arrows, and traps. Sometimes even whole groups can be captured.
The IUCN Red List and other sources don’t provide the number of the Common brown lemur total population size. Currently, this species is classified as Near Threatened (NT) on the IUCN Red List and its numbers today are decreasing.
Common brown lemurs act as important seed dispersers of the plant species they consume. This way they benefit the ecosystem of the dry deciduous forests and rainforests, where they live. They also feed on insects and bird nests and thus, may control populations of these animals.