Red-backed squirrel monkey  (Saimiri oerstedii)

This small monkey has a slender body and a tail that is longer than the body itself. The tail is not prehensile, but it does aid in balance as this monkey leaps between branches in a squirrel-like fashion. The limbs are fairly long and slender, and the thighs are shorter in relation to the lower leg than in species that clamber, such as howler monkeys. This adaptation allows squirrel monkeys to exert more force when jumping and so they can propel themselves further (4). This monkey's fur is short, thick and yellow brown in colour, with the underside being a paler yellow. As its common name, the red-backed squirrel monkey suggests, this primate has red-coloured fur on its back (5). It also bears a distinctive crown on its head; in the black-crowned subspecies (Saimiri oerstedii oerstedii), this crown is, as the name suggests, black, whereas in the grey-crowned Central American squirrel monkey (Saimiri oerstedii citrinellus) it is agouti in the male, and blackish-grey in the female (2) (4). Males and females are similar in appearance, though males are slightly larger in size. During the breeding season males also become ‘fatted', with a noticeable increase in size around the neck and shoulders (4).

The black crowned subspecies has a restricted range along the Pacific coast of the Puntarenas province in south-western Costa Rica, and in Chiriqui and Veraguas provinces, northwestern Panama (2).

The grey crowned subspecies is found in south-western Costa Rica where it has an even more restricted range, of only 210 km², on the Pacific coastal forests of Quepos (1).

This species mainly lives in lowland scrub forest (2), although it also inhabits humid tropical forest, mature upland forest, river edge and mangrove forest (1).

Little is known about the biology of this species. Like other squirrel monkeys it is active during the day and is arboreal (6). This small primate is omnivorous and spends most of the morning and afternoon foraging in the trees for fruits, leaves, buds, gums, insects and small vertebrates (7). It has been reported that this species recognises the leaf-tents constructed by some fruit-eating bats and attacks these structures to extract the bats roosting within (8).

Red-backed squirrel monkeys are social primates. They live in large multi-male / multi –female groups of about two-dozen individuals on average, and travel between 2.5 and 4.2 km a day, with home ranges of 0.175 km² (2) (6) (9). Reproduction is seasonal, with mating occurring in January and February (2), with single births occurring at the period of greatest food availability. This ensures there will be adequate food available for the mothers and their young, and requires less time spent foraging (10).

The grey-crowned subspecies Saimiri oerstedii citrinellus is critically endangered and has lost 89% of its original habitat in Costa Rica, with the remaining range (just 210km²) being severely fragmented (1). This is due to widespread logging and clearing for cattle ranches which started during the 1950s. Large areas were also planted with African oil palms and rice. In Panama, the black-crowned subspecies Saimiri oerstedii oerstedii has also suffered habitat losses of 76%, and now occurs in fragmented forest areas throughout its range (1,166km²) (1).

Like so many species the survival of the red-backed squirrel monkey is inextricably entwined with the future of the forests. Where there are protected reserves, there is hope for South America's wildlife (1). The largest single population of the subspecies Saimiri oerstedii citrinellus occurs in the Manuel Antonio National Park in Panama. However this park is only 683 hectares in size (1). A recent survey (2003) did, however, indicate that the total population size for the red-backed squirrel monkey is significantly larger than had been previously estimated, numbering between 1300 and 1780 individuals (6). It will be extremely important to monitor and protect the remaining populations in the future, and find ways of securing their survival (8).

Authenticated (05/06/2006) by Matt Richardson, independent primatologist and writer.