Geoffrey's spider monkey (Ateles geoffroyi)
Range: Central America
The Geoffrey’s spider monkey is one of the largest New World monkeys, as well as one of the smartest. A 2007 study concluded that spider monkeys were the third-most intelligent nonhuman primate, behind only orangutans and chimpanzees. One example: the Geoffrey’s spider monkey has been seen rubbing a mixture of saliva and ground lime-tree leaves on its fur, which is believed to act as an insect repellent. Each spider monkey makes a unique sound; this helps the monkeys recognize each other, call other group members to food, maintain vocal contact with their group while traveling, and distinguish between group members and nongroup members. These monkeys also use nonvocal communication: A curled tail or arched back may be a threat display, while a head shake is either a threat or an invitation to play; shaking branches or swaying arms is a warning of danger. Habitat loss, hunting, and the pet trade have led the Geoffrey’s spider monkey to be declared endangered.

Researchers have found that Geoffrey’s spider monkey populations decline one year after El Niño events, which affect food availability for these fruit-eaters. Researchers have warned that the intensification of El Niño events due to climate change may further imperil this already endangered primate.