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The family Cheirogaleidae has five genera and 30 species: Microcebus, the mouse lemurs (18 species); Allocebus, the hairy-eared dwarf lemur (one species); Mirza, giant mouse lemurs (two species); Cheirogaleus, the dwarf lemurs (five species); and Phaner, the fork-marked lemurs (four species). No subspecies are recognized at the present time. Cheirogaleid lemurs range in size from the world’s smallest primate at about 30 g to almost 600 g. All move quadrupedally and most have elongated bodies with short legs. At least one species of cheirogaleid can be found in any natural forest of reasonable size in Madagascar.

All members of this family are nocturnal, sleeping during the day in small nests of dead leaves, in tree holes, or in holes in the ground. Some cheirogaleids undergo prolonged periods of seasonal torpor. 

Microcebus É. Geoffroy, 1828 Mouse Lemurs

The genus Microcebus includes the smallest of the lemurs and indeed the smallest of all living primates. These tiny animals range in weight from 30 to 87 g and in length from about 23 to 29 cm (including tail), and all are nocturnal in habit. Until recently, very few species were recognized in this genus. Schwarz (1931), for example, recognized only one with two subspecies. Field work by Martin (1972a) indicated that the two subspecies were in fact distinct species, Microcebus rufus and M. murinus. Petter et al. (1977) continued to recognize two subspecies, but noted that there was geographical variation in both the eastern and western areas of their distribution. Subsequent field studies in western and northern Madagascar in the 1990s led to the resurrection of the name myoxinus (see Schmid and Kappeler, 1994) and the discovery of a new species, M. ravelobensis Zimmermann et al., 1997. Later still, more field work in western Madagascar, coupled with genetic analyses, resulted in the addition of three new species, M. berthae, M. sambiranensis and M. tavaratra, a clarification of the status of M. myoxinus, and the elevation of a previously described subspecies to a full species, M. griseorufus (see Rasoloarison et al., 2000; Yoder et al., 2000b; Hapke et al., 2003a). These researchers also indicated that eastern M. rufus might also include more than a single species, and Groves (2001) drew attention to differences between northeastern and southern specimens within the form recognized as M. rufus. This has now been confirmed by recent field and laboratory studies that have resulted in the description of an additional ten species as we go to press in 2010, all in what was formerly considered the range of M. rufus. These include M. lehilahytsara described in Kappeler et al. (2005), M. danfossi and M. bongolavensis described by Olivieri et al. (2007a), M. mamiratra described by Andriantompohavana et al. (2006), M. jollyae, M. mittermeieri and M. simmonsi described by Louis et al. (2006a), M. macarthurii described by Radespiel et al. (2008), and M. arnholdi and M. margotmarshae described by Louis et al. (2008). In this field guide we provide full accounts for all 18 presently-recognized species while at the same time recognizing that the taxonomy of this genus will continue to undergo further revision. Anticipated are formal descriptions of two more species mentioned in Louis et al. (2006a) (from Manombo and Vevembe, respectively) and one species mentioned in Radespiel et al. (2008). 

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. 

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