Mouse lemurs are present throughout Madagascar wherever suitable natural habitat remains, including primary and secondary forest and even disturbed habitats. They are often among the most abundant mammals in areas where they occur. Typically, mouse lemurs are sympatric with at least one other nocturnal lemur, and very often three, four, or even five. Two Microcebus species may be sympatric in some areas as well.
In the field, Microcebus can be distinguished from Cheirogaleus by its much smaller size and more active movements, and from Mirza by its smaller size. Phaner is larger, much more vocal, and easily distinguished by its fork-mark and its bobbing movements. Lepilemur, Avahi, and Daubentonia are all much larger and cannot be confused with Microcebus. The one genus which presents problems is Allocebus, since both Microcebus and Allocebus are small, and the latter’s hairy ears are only distinguishable if a very clear, close view is obtained. Mouse lemurs tend to use the lower forest layers and to prefer habitat edges, moving quadrupedally and jumping in rapid bursts. During daylight hours, they seek shelter in tree holes, dense tangles of vegetation, or nests, where they congregate in small groups. During the austral winter, certain species may enter periods of daily and seasonal torpor during which they lose a significant percentage of their body mass, previously stored as fat. Their diet consists mainly of fruit, but also includes small invertebrates, gums and insect excretions. Mouse lemurs are preyed upon by several mammals, and by owls, vangas (Vangidae), and snakes.
Home ranges vary from one to two hectares, those of multiple males and females overlapping. Mouse lemurs can begin to reproduce during their first year of life, typically giving birth once or twice (rarely three times) each year, and often producing twins. Much of what is currently known about mouse lemurs is well summarized in Kappeler and Rasoloarison (2003).
There are many opportunities for visitors to Madagascar to see mouse lemurs in the wild, but only if they are willing to don a headlamp or flashlight and embark on a night walk. Be prepared to listen for high-pitched, squeaking vocalizations and to look for the tiny eyes shining back in the beam of your flashlight from the shrub layer up to the middle levels of the forest. However, do not expect the mouse lemur to sit in your beam for too long, as would be the case with the less active Cheirogaleus or Lepilemur. Mouse lemurs are active and will move away from the light, although you can usually follow them for short distances. Occasionally, with a little luck, one will freeze in the beam of your light, allowing you to approach to within a meter or so and perhaps even take a photo.