Ateles hybridus

The brown spider monkey has long slender limbs, with the forelimbs being longer than the hindlimbs. It has a unique and flexible, slender, sessile tail about 75 cm long. The tail is used like a fifth hand, with a highly flexible, hairless tail tip having skin grooves to improve grip. Its fingers are curved, with a pinky but small. These features enable it to climb trees at high altitudes, hang and swing from trees without the need to come back to the ground often. Adult males weigh between 7.9-9.1 kg, and adult females weigh between 7.5-9 kg. Its average adult body length is 50 cm. Its color ranges from light brown to darker on the upper parts including the head. Its most distinctive feature is a white triangular patch on the forehead, although not all individuals have it. Some have light blue eyes, but most are brown.

The brown spider monkey is found in the departments of Magdalena and Cesar on the right bank of the Magdalena River in Colombia, in the northernmost part of Serrania de Perija in the southwest of Guajira Province, and in the central valley of the Magdalena River at least to the departments of Caldas and Cundinamarca. In Venezuela, the brown spider monkey is usually found between 20 and 700 meters above sea level.

The brown spider monkey, scientifically known as Ateles hybridus, is also known as the spotted spider monkey. It is a critically endangered species of spider monkey and a type of New World monkey.

Although the brown spider monkey spends most of its time in trees, it occasionally comes down the mountain to eat soil and drink water. As it forages high in the canopy, it prefers undisturbed primary forests. The Brown Spider Monkey travels in small groups and does not walk or run on all fours, but mainly travels by swinging and climbing between trees.

The Brown Spider Monkey forages mainly in the forest canopy, relying mainly on sight, smell, taste and touch to find food. It is primarily herbivorous and frugivorous. A major component of the Brown Spider Monkey's diet is ripe fruit. More than three-quarters of its diet is lipid-rich fruit. It plays an important role as a seed disperser in the ecology, as habit relationships can help disperse a large number of seeds of canopy tree species and vines. However, during the dry season when fruits are less common, it feeds on leaves, seeds, flowers, bark, honey, rotting wood, and occasionally insects such as termites and caterpillars. Scientists have observed it also eating soil and clay, and speculate that the reason for this behavior may be to obtain minerals such as phosphorus from the soil, or to maintain the pH balance of its digestive system. Brown spider monkeys also find water to drink on the forest floor, and competition for food occurs with other primates.

Brown spider monkeys live in multi-male/multi-female groups of about 30 individuals. However, they are rarely seen together, and most of the time they travel, forage, and rest in small groups of varying sizes and compositions. The average estrus period for each brown spider monkey is only 26 days per year, and it takes males about 3 days of courtship to mate with females, and mating lasts 5 to 10 minutes. One offspring is born per litter. The young are weaned at 20 months, during which time the females will not mate again. Although some brown spider monkey populations seem to have the majority of births in certain months of the year (May-December for white-bellied spider monkeys in TBS, Ecuador), there is no information on the seasonality of births in brown spider monkeys. Females disperse from their birthing group at about 6 years of age and reach sexual maturity at about 8-9 years of age. They give birth to one offspring after a long gestation period of 226-232 days, with an average birth interval of 32-36 months. Late maturation and long birth intervals make them difficult to recover from hunting and other threats. The average lifespan of the brown spider monkey is 27 years, however, in captivity, it can live up to 40 years. Predators include jaguars, mountain lions, harpy eagles, and crested eagles. The brown spider monkey will shake branches to ward off potential predators.

The brown spider monkey is one of the most threatened primates in the Neotropics. It is estimated that the number of brown spider monkeys has decreased by at least 80%, and some populations have become extinct. Few of the remaining populations are large enough to survive long-term. In 2010, nearly 60 brown spider monkeys were recorded in various zoos participating in the International Species Information System (mainly in Europe), but reproduction is slow. Habitat loss is ongoing throughout its wild range, with an estimated 98% of its habitat gone. Habitat loss is caused by logging, land clearing for agriculture, and ranching. It is also threatened by hunting (where it is most popular in some areas) and the wildlife trade. One study did not show a clear difference in population density between those within and outside of forest areas disturbed by loggers. It is speculated that this anomaly is due to the samples being taken from the El Paujil Reserve, which is a protected area and may be a refuge from other human activities (i.e. poaching).

A small population of less than 30 individuals has been found in a protected area in Colombia, the Selva de Florencia National Natural Park. This is the southernmost population of the Brown Spider Monkey. The Brown Spider Monkey has also been found in other protected areas in Colombia and Venezuela.

The brown spider monkey is one of the most threatened primates in the neotropics and has been listed in the "World's 25 Most Endangered Primates" six times.

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