The Amazon dwarf squirrel (''Microsciurus flaviventer'') is a

chipmunk Chipmunks are small, striped rodents of subtribe Tamiina. Chipmunks are found in North America, with the exception of the Siberian chipmunk which is found primarily in Asia. Taxonomy and systematics Chipmunks are classified as four genera: '' ...

-sized

tree squirrel Tree squirrels are the members of the squirrel Family (biology), family (Sciuridae) commonly just referred to as "squirrels". They include more than 100 arboreal species native to all continents except Antarctica and Oceania. They do not form a ...

native to

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

Description

As its name suggests, the Amazon dwarf squirrel is relatively small, with a head-body length of and a tail long. Adults weigh between , with males being slightly larger than females. The fur varies from reddish to dull brown, fading gradually to yellow or greyish on the underparts. There is a distinctive patch of pale yellow fur behind the ears, while the tail has faint yellowish bands and white frosting. The limbs are unusually long for tree squirrels. In the forelimbs, the

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

and

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

are of equal length, an adaptation thought to increase the squirrel's ability to climb large trees, compensating for a lack of shoulder mobility. The longer hindlimbs allow for stronger muscles, so that the squirrel can leap over larger gaps, relative to its size, than more typically sized squirrels can.

Distribution and habitat

The squirrels are found in the upper Amazon Basin, broadly west of the Purus and Rio Negro rivers, in

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...

, and

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

. They typically inhabit evergreen

tropical rainforest Tropical rainforests are dense and warm rainforests with high rainfall typically found between 10° north and south of the Equator. They are a subset of the tropical forest biome that occurs roughly within the 28° latitudes (in the torrid zo ...

s at up to elevation, although they may sometimes be found in more disturbed habitats.

Subspecies

Eight subspecies of Amazon dwarf squirrel are generally recognised. Recent studies have indicated that the

subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

''M. f. otinus'', ''M. f. sabanillae'', ''M. f. similis'', and ''M. f. simonsi'' are their own distinct

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

rather than subspecies. The same study also showed that ''M. f. otinus'' and ''M. f. similis'' are more closely related to '' Microsciurus mimulus'' and '' Sciurus pucheranii'' than they are to ''M. flaviventer''.

Biology and behaviour

The squirrels use all levels of the forest, from the ground to the tree canopy, but are most commonly found in the

understory In forestry and ecology, understory (American English), or understorey (English in the Commonwealth of Nations, Commonwealth English), also known as underbrush or undergrowth, includes plant life growing beneath the Canopy (biology), forest ca ...

. They feed on arthropods, tree bark, and fungi, and have been observed to closely follow flocks of birds while foraging, although the reason for this is unclear. They are diurnal and highly

arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...

, even for tree squirrels, frequently jumping from branch to branch. They spend the night in nests formed from plant fibres, and located several metres above the ground. They are mostly solitary, but may be found with others feeding on the same tree. Their calls include a bird-like "trill" and a series of soft "chucks" used as an alarm call. Very little is known of their reproduction, although litters are thought to be small.

References

Bibliography

* Tirira, Diego. 2006. Mamíferos del Ecuador, Diversidad: Microsciurus flaviventer (Gray, 1867). Page on internet (Enero 2006). Version 1.1. Ediciones Murciélago Blanco. Quito
Mamiferos del Equador
Checked on: fecha de visita (2009-03-17)

External links

{{Taxonbar, from=Q1769291 Microsciurus Rodents of Brazil Mammals of Bolivia Mammals of Colombia Mammals of Ecuador Mammals of Peru Fauna of the Amazon Mammals described in 1867 Taxa named by John Edward Gray