White-cheeked spider monkey.

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The white-cheeked spider monkey, also known as the white-whiskered spider monkey, is endemic to the Amazon Basin in central Brazil, residing in the lush, biodiverse lowland rainforests. They share their genus with six other species of true spider monkeys, named after their extremely long arms and legs that are adapted to life in the trees. On average, white-cheeked spider monkeys weigh about 13 lbs (5.8 kg) and are 13–20 inches (34–51 cm) in length, not including their tails. Their average life span is about 20 years.

White-cheeked spider monkeys are mostly dark brown or black, with white hair on their forehead, chin, and cheeks. They have extremely long arms and legs, a prehensile tail that helps them swing from branches, and a hairless, textured underside of their tail. They lack external thumbs, instead using their hands like hooks, a specialized adaptation to their arboreal lifestyle.

White-cheeked spider monkeys are highly frugivorous, with fruits comprising 83% of their diet. They supplement with young leaves and flowers, seeds, aerial roots, bark, decaying wood, honey, and occasionally small insects. They are diurnal and exclusively arboreal, spending most of their lives in the upper levels of the canopy. They are known for being suspensory, hanging from branches and using both hands to forage.

White-cheeked spider monkeys live in large groups with an average size of 25 individuals, but most of the time, they break out into smaller groups (usually two to four individuals) to travel, feed, and rest together, forming a social system called “fission-fusion.” These small groups are fluid, with individuals moving about and forming new sub-groups frequently, even changing several times per day. The subgroups are led by a dominant female, and each female in the group has a core area within the group’s territory that she uses most.

This social structure may have evolved as a strategy to reduce competition for food within a group. Small groups that forage together compete less on a single tree than a large group that forages together, and they still have the benefit of increased mating opportunities and protection from predators that comes from associating with the large group. Relations within a group are usually peaceful, with scraps occurring when competition over food is brief and does not result in injury.

Spider monkeys are a unique species that have evolved to communicate with each other and other animals. They use a behavior called “bridge-gapping” to help a juvenile cross a large gap between trees, and they communicate through barking and shaking nearby tree branches. Their reproductive system is not well studied, but they are believed to be polygynous, with males mating with multiple females and females mating with only one male. The offspring reach sexual maturity at 4-5 years of age, making it difficult for the population to recover from hunting and other threats.

Females are the primary caregivers of young, carrying infants on their stomachs for the first six months of life, then on their backs for at least another six months. Offspring become increasingly independent from their mothers, relying on them for transportation only when they’re fatigued or to cross a particularly long gap between trees. By three years of age, spider monkey young are fully weaned, but they remain with their mother for another year or two. Upon reaching independence, females disperse to new groups to find mating opportunities, while males typically remain with their natal group.

White-cheeked spider monkeys play an important ecological role as frugivores, depositing seeds of 138 plant species, a full 94% of the species they consume. They are vulnerable to predation by raptors, jaguars, and large snakes due to their relatively large bodies.

White-cheeked spider monkeys are considered Endangered by the International Union for Conservation of Nature, appearing on the IUCN’s Red List of Threatened Species (IUCN, 2019). This categorization is based on a predicted population loss of about 50% between 2006 and 2050, primarily due to deforestation and hunting pressure. Habitat loss is the most urgent threat, with nearly 100 mammal species in the Brazilian Amazon expected to lose more than 40% of their protected habitat and up to 80% of their unprotected habitat by 2050.

Conservation efforts include protecting white-cheeked spider monkeys in protected areas such as Altamira National Forest, Terra do Meio Ecological Station, and Jamanxim National Forest, which are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES).