Monkeys » Black-handed Spider Monkey
Scientific Name: Ateles geoffroyi
The Black-handed Spider Monkey is listed as a vulnerable species and population estimates from Biologist Ronald Sanchez at the University of Costa Rica show a 72% decline in their population over 12 years from 26,000 individuals in 1995 to 7,225 individuals in 2007. This species is very susceptible to human interference in its environment and because females reproduce on average only every three years it is difficult for groups to recuperate quickly from adverse environmental effects. As populations decline the possibility for inbreeding increases with the potential to cause genetic deficiencies in the species.
The prehensile tail of the spider monkey is muscularly adapted for controlled grasping or wrapping around branches like a third arm. The tail of this species is one of the strongest in the animal kingdom and can support more than its entire body weight. Their thumb less hands act as hooks for grasping and swinging agilely from branch to branch and for pulling fruit-laden branches to their mouths.
Their name originates from their extra long arms and legs that look like spiders’ legs. The females have a large pendulum like clitoris that could be mistaken for a male’s penis. This species occasionally associates in the wild with the White-throated Capuchin monkey.
This species can be found in evergreen rain forest, semi deciduous forest, and mangrove forest but prefers primary forest below 8,000 feet (2,500 meters) in altitude.
Their diet consists of 78% fruits, 12% flowers, and 10% other nutritional sources such as young leaves, buds, mature leaves, insects and animal prey.
This species normally produces only a single baby and it is not weaned from the mother until about one year old. This factor leads this species to have a long birth interval of about 3 years. Young monkeys are considered infants up to 2 years old and they do not reach sexual maturity until 4 to 5 years. The gestation period is an average of 225 days. For the first 1.5 to 2 months the baby rides on the mother’s stomach and then begins to ride on her back for the next few months. The ratio of males/females born is 1:1.8 which signifies that for every male born there are 1.8 females born. The average lifespan is 27 years.
The average group size varies from 4 to 35 depending on the availability of food resources. When resources are limited the larger community divides into small subgroups to search for food. With a male to female birth ratio of 1:1.8 there are almost twice as many females in a group than males. Groups do not normally accept new individuals from another group. Often the group will kill a newly introduced monkey. That is why it would be very dangerous to release these monkeys back into their natural environment and why we take great care to slowly introduce our rescued monkeys to each other.
A group’s territory can range from 150 acres (62 hectares) to 250 acres (100 hectares). Their day range falls between 1,150 feet (350 meters) and 9,850 feet (3,000 meters). Males travel farther than females each day perhaps increasing their chances of encountering other females. Females with infants travel the least.
In this species males actually pay more attention to each other than the females. Friendly interactions between males account for 85% of a male monkey’s friendly interactions leaving only 15% for male to female interaction. According to studies they spend 54% of their time resting, 28% of their time traveling, 11% feeding, and 7% of the time interacting with each other. They have a very complex communication system that includes facial expressions, body language, chemical signals and various vocalizations.