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Myosciurus pumilioAfrican pygmy squirrel

By Leanne Burns

Geographic Range

Myosciurus pumilio is found in western Central Africa in the countries of Cameroon, Gabon, northwestern Congo, and Equatorial Guinea, including the island of Bioko. Their range is not well characterized and may be larger than presently recognized. (Gharaibeh and Jones, 1996; Jones and Setzer, 1970; Nowak, 1999; "African Pygmy Squirrel (Myosciurus pumilio)", 2009)

Habitat

African pygmy squirrels are arboreal and found in all types of central African forests within their range. They have been observed from the floor to the canopy, but apparently prefer lower levels of the canopy, spending the majority of their time at heights of 0 to 5 meters. They spend their inactive time in exposed leaf-nests. (Emmons, 1980; Gharaibeh and Jones, 1996; Nowak, 1999; "African Pygmy Squirrel (Myosciurus pumilio)", 2009)

Physical Description

African pygmy squirrels share many of the distinctive tree squirrel characteristics, such as having longer hindlimbs than forelimbs, a skull with an arched profile, ever-growing incisors, rooted cheek teeth, and a sciurognathus lower jaw. They are the smallest squirrel in the world. The average adult weight is 16.5 grams. Their small body size is believed to be an adaptation to access bark on every tree surface, allowing these squirrels to move as easily on the underside of a branch as the top surface. Their small size differentiates them from other African sciurids. The largest skull ever recorded was less than 25 mm in length. The masseteric tubercule of M. pumilio is absent, and the palate does not extend beyond the ends of the maxillary toothrow. There is one premolar in each side of the upper jaw. The dental formula is 1/1, 0/0, 1/1, 3/3 = 20. Due to a smaller brain size and thus a reduced zygomatic arch, the arrangement of the masseter is very similar to that of neotropical pygmy squirrels (Sciurillus pusillus) with a more anterior insertion of the anterior deep masseter. In both species the zygomatic plate and muscle fibers are oriented more vertically than in larger squirrels increasing the strength of the incisor bite. The length of head and body is 60 to 75 mm, while the length of tail is 50 to 60 mm. The pelage of M. pumilio is soft with buffy green upper parts and an olive white underside. They have fluffy tails. The borders of the eyelids and the edges of their rounded ears are white. A slight sexual dimorphism has been observed, with female body size moderately smaller then males but male cranial measurements slightly smaller than females. (Emmons, 1980; Gharaibeh and Jones, 1996; Jones and Setzer, 1970; Nowak, 1999; "African Pygmy Squirrel (Myosciurus pumilio)", 2009; Thorington and Darrow, 1996)

  • Sexual Dimorphism
  • male larger
  • Average mass
    16.5 g
    0.58 oz
  • Range length
    60 to 75 mm
    2.36 to 2.95 in

Reproduction

Little is known of the mating systems of M. pumilio. In general, arboreal squirrels have a polygamous mating system, with males competing for access to females who are sexually receptive for less than a day. Males must chase females, who avoid them as long as possible. Eventually the female will accept the most competitive male, and they will mate in a sheltered area to lessen the threat of attack or injury during copulation. ("Squirrels and Relatives III: Tree Squirrels", 2009)

Little is known about reproduction in African pygmy squirrels. Limited data indicate a four-month period of little or no breeding. Few pregnant or lactating females have been observed so information is limited. There are records of two pregnant females, each with two embryos, being captured as well as a lactating female captured in early spring. Based on these specimens, pairs of mammae seem to vary from 1 to 2 and it has been suggested that breeding occurs early in the year. (Emmons, 1979; Gharaibeh and Jones, 1996; Jones and Setzer, 1970)

  • Breeding interval
    Breeding interval in African pygmy squirrels is unknown.
  • Breeding season
    Breeding in African pygmy squirrels appears to be concentrated seasonally, but there is little information on seasonality.
  • Average number of offspring
    2

Female African pygmy squirrels provide all parental care through gestation, lactation, and protecting their young. There is no information available regarding time to weaning and the duration of dependence for the young of M. pumilio. (Emmons, 1979; Emmons, 1979; Emmons, 1979; Emmons, 1979; Emmons, 1979; Emmons, 1979; Emmons, 1979; Emmons, 1979; Emmons, 1979)

  • Parental Investment
  • altricial
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

There is no information available regarding the lifespan of M. pumilio. Larger squirrels have maximum lifespans of 9 to 15 years. (Nowak, 1999; "Squirrels and Relatives III: Tree Squirrels", 2009)

Behavior

African pygmy squirrels are arboreal, diurnal squirrels that spend much of their time foraging, doubtless due to their diminutive size. Individuals habitually forage in trees, running quickly over their trunks and pulling off small pieces of the outer bark. They are the only species of squirrel that travels frequently both upside down and right-side up along branches. Although they are mainly solitary, when observed in close proximity, individuals tolerate each other. Unlike many other species of squirrel they do not participate in mobbing predators. (Emmons, 1980; Gharaibeh and Jones, 1996; Jones and Setzer, 1970; "African Pygmy Squirrel (Myosciurus pumilio)", 2009)

Home Range

There is no information on home range sizes in the literature.

Communication and Perception

Although African pygmy squirrels are solitary, a low-intensity alarm vocalization that is described as a “faint pipping sound,” has been recorded, seeming to call attention to nearby danger. When repeated, these single calls vary little in frequency or in length of the interval between calls. These calls may warn offspring or nearby animals of a threat. Like all squirrels, they have keen vision, hearing, and sense of smell. They use vibrissae on their bodies to help them navigate on tree trunks and branches. (Emmons, 1980; Gharaibeh and Jones, 1996; Jones and Setzer, 1970)

Food Habits

African pygmy squirrels are omnivorous, bark gleaners who forage incessantly. They eat scrapings from bark after pulling small chips off the surface of trees, as well as insects and fruit. Stomach contents include bark fragments, fungus, oil droplets, termites, ants and some fruit fragments. It is hypothesized that a microscopic fungus with oily spores may be the primary food substance these squirrels obtain from the bark. Unlike most other squirrels, African pygmy squirrels do not cache food. (Emmons, 1980; Gharaibeh and Jones, 1996)

  • Animal Foods
  • insects
  • Plant Foods
  • wood, bark, or stems
  • fruit
  • Other Foods
  • fungus

Predation

Active African pygmy squirrels most likely fall victim to birds of prey, such as hawks and falcons. Nocturnal nest predators include snakes, army ants, and civets. African pygmy squirrels are cryptically colored and remain vigilant to protect themselves from predators. (Emmons, 1980; "Squirrels and Relatives III: Tree Squirrels", 2009)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

African pygmy squirrels are bark gleaners. Because of their small size and scarcity they seem to have little impact on the ecosystem around them, although their reliance on a tree fungus could impact the distribution of that fungus, which may in turn affect tree growth. Nothing is known about parasitic faunas on African pygmy squirrels. (Emmons, 1980)

Economic Importance for Humans: Positive

The positive economic importance of M. pumilio for humans is unknown.

Economic Importance for Humans: Negative

There are no known adverse effects of African pygmy squirrels on humans.

Conservation Status

In 1989 African pygmy squirrels were classified as vulnerable because of low numbers and susceptibility to deforestation due to their small geographic range. Currently they are considered Data Deficient by the IUCN until more is known regarding population numbers. The IUCN views deforestation and habitat degradation as the main threat to this species, because it directly reduces their habitat. African pygmy squirrels are not currently protected by legislation, but sanctuaries across their range are a vital way of conserving this species. The IUCN has emphasized the need for further research into M. pumilio population numbers and exact range. (Nowak, 1999; "African Pygmy Squirrel (Myosciurus pumilio)", 2009)

Other Comments

African pygmy squirrels were previously known by the scientific names Myosciurus minutus, Myosciurus minutulus, Sciurus pumilio, and Sciurus minutus, until Myosciurus pumilio was adopted as the current name combination. Due to the limited number of specimens and research, much is still unknown regarding M. pumilio. There is no fossil record and no genetic data available for this species. (Gharaibeh and Jones, 1996)

Contributors

Leanne Burns (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mycophage

an animal that mainly eats fungus

native range

the area in which the animal is naturally found, the region in which it is endemic.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

The Zoological Society of London. 2009. "African Pygmy Squirrel (Myosciurus pumilio)" (On-line). Edge Evolutionarily Distinct and Globally Endangered. Accessed April 06, 2009 at http://www.edgeofexistence.org/mammals/species_info.php?id=582.

The Gale Group, Inc. 2009. Squirrels and Relatives III: Tree Squirrels. Pp. 163-175 in Grzimek's Animal Life Encyclopedia, Vol. 5, 2nd ed Edition. Michigan: The Gale Group, Inc.. Accessed April 06, 2009 at http://www.answers.com/topic/squirrels-and-relatives-iii-tree-squirrels-biological-family#copyrights_ans.

Emmons, L. 1980. Ecology and Resource Partitioning among Nine Species of African Rain Forest Squirrels. Ecological Monographs, 50/1: "31-54".

Emmons, L. 1979. Observations on Litter Size and Development of Some African Rainforest Squirrels. Biotropica, 11/3: "207-213".

Gharaibeh, B., C. Jones. 1996. Myosciurus pumilio. Mammalian Species, 523: "1-3".

Jones, C., H. Setzer. 1970. Comments on Myosciurus Pumilio. Journal of Mammalogy, 51/4: "813-814.

Nowak, R. 1999. Rodentia ; Sciuridae, Genus Myosciurus. Pp. "1282-1284" in Walkers Mammals of the World, Vol. 2, 6 Edition. Baltimore: Johns Hopkins University Press.

Thorington, R., K. Darrow. 1996. Jaw Muscles of Old World Squirrels. Journal of Morphology, 230: "145-165".

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