Saimiri oerstedi

Adult red-backed squirrel monkeys are 27-29 cm long, with a tail length of 36-39 cm and a weight of 600-950 grams. Males are slightly larger.
The red-backed squirrel monkey has an orange back, hands and feet, olive shoulders, hips and tail, and a white belly. The skull cap is black, and the tip of the tail is also black. The face is white, and the area around the eyes, nose and mouth is black. Their tails are not completely grasping, but are mainly used for balance. The skull cap of males is generally lighter than that of females. They have the largest brain-to-body ratio of all primates, with a brain weighing about 25.7 grams or 4% of their body weight.
The two subspecies of red-backed squirrel monkeys are similar in color, but the shape of their skull caps is different. The northern subspecies has a lighter skull cap. The southern subspecies has yellower limbs and abdomen.

The red-backed squirrel monkey is found only in Costa Rica and Panama. They live along the Pacific coast, from central Costa Rica to western Panama. They can be found in Manuel Antonio National Park and Cortes del Cristo National Park. They live in lowland secondary and primary forests and have difficulty surviving in taller, mature forests.

The scientific name of the red-backed squirrel monkey is Saimiri oerstedi. There are two subspecies: 1. S. o. oerstedii: distributed on the western Pacific coast of Panama and the Osa Peninsula of Costa Rica. 2. S. o. citrinellus: distributed in central Costa Rica, with an estimated number of only 1,300-1,800 left.

Red-backed squirrel monkeys are diurnal and arboreal, often walking on four legs in trees. Their groups consist of several adult males, females, and infants. The number is less than other South American squirrel monkeys, but it is still considered large among New World monkeys. The number of groups ranges from 20 to 75, with an average of 41. Sometimes some groups have more than 100 individuals, but it is believed that this is just a temporary combination of two groups. On average, females outnumber males in a group by 60%.

Red-backed squirrel monkeys are omnivorous, eating mainly insects and their larvae, spiders, fruits, leaves, bark, flowers and nectar. They also eat small vertebrates such as bats, birds, lizards and frogs. They forage in the middle to lower levels of the forest, which is 40-50 feet high. They spend about two-thirds to three-quarters of their day eating. During the rainy season, it is difficult for them to find the food they want to eat because there are fewer arthropods.

Red-backed squirrel monkeys are noisy and often scream, whistle and chirp. They break branches as they pass through the forest, making a lot of noise. The natural enemies of red-backed squirrel monkeys include birds of prey, cats and snakes, of which birds of prey are the most effective in catching them.

The breeding season for red-backed squirrel monkeys is in September. It is the female monkeys who choose the male monkeys for mating. Female monkeys may choose larger male monkeys. The gestation period is 6 months, and the baby monkeys are born within a week between February and March. They give birth to one baby monkey per litter. Only half of the baby monkeys can survive more than 6 months, mostly due to bird predation. The baby monkeys need to rely on the care of the mother monkeys for the first year. Female monkeys can give birth every 12 months, so the baby monkeys born before can be independent when the new baby monkeys are born. Female monkeys reach sexual maturity at 2.5 years old, while male monkeys reach sexual maturity at 4-5 years old. Female monkeys will leave their group after sexual maturity, while male monkeys will stay in the group for their entire lives. Male monkeys tend to contact male monkeys of the same age. Male monkeys of the same generation can choose to leave the group after sexual maturity and seek greater reproduction opportunities in other groups. The life span of red-backed squirrel monkeys in the wild is unknown, but they can live to more than 15 years in captivity.

The IUCN Red List lists them as vulnerable (VU).

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