PYGMY MOUSE LEMUR
Geographic Distribution and Habitat
Originally described in 1858, the pygmy mouse lemur (Microcebus myoxinus), also known as Peters’ mouse lemur, dormouse lemur, or western rufous mouse lemur, was thought to be extinct until its rediscovery in the Kirindy Forest of Madagascar in 1993. Like all lemurs, they are endemic to the island of Madagascar. They make their homes in the dry deciduous forests along the northwest portion of the island, and they may also live in mangrove forests. Their range is believed to be between the north bank of Tsiribihina River and continuing north to Baie de Baly National Park. They live at elevations from sea level to 2,900 feet (900 m).
The taxonomy of the Microcebus genus is fluid, with species frequently getting reclassified or separated as more research is conducted. As of right now, there are believed to be about 24 species comprising Microcebus. They diverged from one another relatively recently in their evolutionary timeline as a result of habitat fragmentation and natural barriers. Because of this, mouse lemurs share many of the same characteristics.
Size, Weight, and Lifespan
As their name implies, pygmy mouse lemurs are extremely small. They come in at a diminutive 2.4 inches (6.1 cm) in head and body length, with their tail adding just 5.4 inches (13.6 cm) on average—about the size of a gerbil. They weigh just 1.1 ounces (30.6 g) on average, roughly the weight of a AA battery. Females are heavier than males most of the year, except during the mating season when males gain weight through enlargement of their testes. Pygmy mouse lemurs typically live between six and eight years in the wild.
A mating system in which both males and females have multiple mating partners during a breeding season.
A sleep-like state in which the body decreases physiological activity
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Their minute size, contrasting with their large eyes and ears, gives the pygmy mouse lemur an extremely charming appearance. They have reddish-brown fur over their bodies, with a cream-colored underbelly. They have a white stripe running vertically between their eyes to their nose. Their snout is short and pointed, and their ears are tall and very mobile. Their limbs are relatively short compared to the size of the body, and the forelegs are slightly shorter than the hindlegs. Their petite hands have an almost frog-like appearance, with the tips of their fingers ending in wide pads. The only form of sexual dimorphism expressed in pygmy mouse lemurs is ear length: males’ ears are longer than females’.
Pygmy mouse lemurs are mostly frugivorous, supplementing their fruit-based diet with flowers, gums, and small insects. They avoid leaves, because in their dry climate, many plants produce toxins to defend from leaf-eating animals. Because of the pygmy mouse lemur’s small size, these toxins could quickly become lethal if consumed.
Behavior and Lifestyle
Like all mouse lemurs, pygmy mouse lemurs are arboreal (tree-dwelling) and nocturnal (active at night) animals. They move about quadrupedally, running and jumping through the trees. They sometimes sleep in tree holes, but may also spend the day sleeping out in the open. Most of their time is spent in cool, dry places such as tangles of tree branches and abandoned lemur nests.
Pygmy mouse lemurs engage in daily torpor lasting about nine hours per day during the dry season. In this hibernation-like state, their metabolic rate and body temperature drop drastically. Their metabolism may reduce by as much as 90%, and their body temperature can drop almost as low as their surroundings. This state helps them to survive periods of food scarcity by reducing their calorie needs. Interestingly, there is no clear pattern as to which individual lemurs will engage in torpor. Some populations of mouse lemurs enter torpor when other populations don’t. Even within the same population, some individuals simply do not enter torpor while others do.
The pygmy mouse lemur is considered by some sources to be the world’s smallest primate, and by others as second only to Madame Berthe’s mouse lemur (M. berthae).
Pygmy mouse lemurs are solitary primates, typically spending their nights foraging alone and their days sleeping alone. Their daily activity levels, metabolism, body temperature, and body mass all tend to vary greatly throughout the year, as they adapt to seasonal variations in their environment.
Male pygmy mouse lemurs don’t defend a territory, instead they roam around their home range to find receptive females to breed with. Male home ranges are about 4.4 times larger than females’ on average, and they sometimes intersect with other males’ ranges during the breeding season. Occasionally, male pygmy mouse lemurs travel together. Their largely solitary social system is likely an evolutionary response to predation—being in a group would draw more attention from predators—and to reduce competition for safe sleeping sites, which are limited and crucial for raising offspring.
Communication methods of nocturnal primates tend to be under-studied, and the pygmy mouse lemur is no exception. A related species, the Sambirano mouse lemur (M. sambiranensis) is known to use whistles, purrs, and chitters to communicate. Most likely, pygmy mouse lemurs use similar vocalizations.
Pygmy mouse lemurs have two breeding periods during the year—once in the spring, between May and June, and once in the fall. Some sources pinpoint the fall breeding season as between September and October, while other sources say November and December. During the breeding season, male testes enlarge significantly. In fact, male pygmy mouse lemurs have the largest testes relative to their body mass of any primate species. After copulation, the male leaves a mating plug in the female’s vagina to prevent her from mating with any other males. The use of the mating plug is a reflection of the species’ polygynandrous mating style, in which both males and females take multiple mates. By preventing the female from mating again, the male can increase his odds of fathering offspring. Female pygmy mouse lemurs give birth to one or two offspring after a 50 to 62 day gestation period, and young are weaned after about 60 days. The generation time for pygmy mouse lemurs is about five years.
Pygmy mouse lemurs are known to live sympatrically with gray mouse lemurs (M. murinus). Being so small, pygmy mouse lemurs are predated upon by many types of animals, including raptors, civets, mongooses, snakes, and even domestic dogs. Owls are a particularly effective predator of mouse lemurs. One study found that a gray mouse lemur population suffered a 25% population loss each year exclusively due to owl predation. As frugivores (fruit-eaters), they serve an important function to forest health as seed dispersers.
Pygmy mouse lemurs are considered Vulnerable to extinction by the International Union for Conservation of Nature (IUCN, 2012). This classification is because the species is believed to have had a population decline of more than 30% over the past 15 years (composing three generations). This decline is due to habitat loss and degradation due to unsustainable agriculture practices, and because this problem will likely continue, they are expected to decline further. The degradation of the habitat has led to the population being extremely fragmented.
Sadly, pygmy mouse lemurs are far from the only species impacted from habitat loss in Madagascar. It is believed that only about 10% of the island’s original forests remain intact, with a staggering 1–2% of the remaining forests being lost each year. The island is an extremely high priority for conservation, because it is home to more than 250,000 species that are found nowhere else in the world.
Pygmy mouse lemurs are protected by two national parks: Tsingy de Bemaraha and Tsingy de Namoroka. They are listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), a listing reserved for those species most at risk of extinction. Further research goals are mainly focused on pinpointing the species’ distribution and habitat. For example, to determine whether the species thrives in mangrove forests. Habitat loss in Madagascar is mainly due to subsistence farming, and because Madagascar is one of the poorest countries in the world, it is clear that any effective conservation programs for this biodiversity hotspot must involve cooperation with the local Malagasy people.
- Dammhahn, M. and P. M. Kappeler. 2008. Small-scale coexistence of two mouse lemur species (Microcebus berthae and M. murinus) within a homogeneous competitive environment. Oecologia, 157(3), 473–483. https://doi.org/10.1007/s00442-008-1079-x
- Hending, D., M. Holderied, G. McCabe. 2017. The use of Vocalizations of the Sambirano Mouse Lemur (Microcebus sambiranensis) in an Acoustic Survey of Habitat Preference. International Journal of Primatology, 38(4), 732–750. https://doi.org/10.1007/s10764-017-9977-6
Written by K. Clare Quinlan, November 2020