Black-headed spider monkey (Ateles fusciceps)
Spider monkey is the common name for the arboreal, tropical New World monkeys comprising the genus Ateles of the primate family Atelidae, characterized by very long, prehensile tails, long arms, and thumbless hands. Found in tropical forests from southern Mexico to Brazil, spider monkeys belong to the subfamily Atelinae with the woolly spider monkeys (genus Brachyteles) and the woolly monkeys (genus Lagothrix).
With their unique forms, great agility, and social behaviors, spider monkeys add greatly to the human enjoyment of nature. Ecologically, they play a role in food chains, consuming fruits and nuts and being consumed by jaguars, harpy eagles, or small cats such as ocelots. However, they are particularly effective as seed dispersers, both in terms of quantity (large number of seeds) and quality (high per capita seed survival) (Russo and Augspurger 2002).
As they require large tracts of undisturbed forest and specialize on ripe fruits, spider monkeys may be considered an indicator species; the monkeys are threatened by habitat destruction through continued agriculture and residential development.
Spider monkeys are New World monkeys. New World monkeys are one of three major informal groups of the biological order Primates, the other two groups being (1) prosimians and (2) monkeys and apes of the Old World. Together, the New World monkeys and the Old World monkeys and apes are considered to be "higher primates," or simians (infraorder Similformes), while the prosimians (such as lemurs) are considered to be the "lower primates." The term monkey thus refers to any simian that is not an ape or any primate that is neither an ape or a prosimian. In reality, monkeys are not a single coherent group and therefore do not have any particular traits that they all share. The New World monkeys are found in Mexico, Central America, and South America, and the Old World monkeys are located in Africa, central to southern Asia, Japan, and India.
There are four families of New World monkeys: Cebidae, Aotidae, Pitheciidae, and Atelidae (Groves 2001). The four families are ranked together as the Platyrrhini clade. All New World monkeys differ slightly from Old World monkeys in many aspects, but the most prominent of which is the nose. This is the feature used most commonly to distinguish between the two groups. The scientific name for New World monkey, Platyrrhini, means "flat nosed," therefore the noses are flatter, with side facing nostrils, compared to the narrow noses of the Old World monkey.
Most New World monkeys have long, often prehensile tails. Many are small, arboreal (live in trees), and nocturnal (active at night). Unlike most Old World monkeys, many New World monkeys form monogamous pairs, and show substantial paternal care of young.
Spider monkeys belong to the Atelidae family with the howler and woolly monkeys and the woolly spider monkeys. They are placed in the Atelinae subfamily with the woolly monkeys (genus Lagothrix) and the woolly spider monkeys (genus Brachyteles]]). The primary distinguishing feature of the atelines is their long prehensile tail, which can support their entire body weight. Diurnal and arboreal, they move speedily and acrobaticly through the trees using their prehensile tail. Atelines, along with their cousins the howler monkeys, are the largest of the New World monkeys.
Adult spider monkeys reach an average body length of 50 centimeters (20 inches) and a weight of 6.4 kilograms (14 pounds). Their heavy fur is coarse and may be brown, reddish-brown, reddish, black, gray, or a ruddy gold. The hands and feet are usually black. Heads are small with hairless faces.
Spider monkeys have disproportionately long, spindly limbs, which inspired their common name. These deftly prehensile tails may measure up to 90 centimeters (3 feet) and have highly flexible hairless tips complete with skin grooves similar to fingerprints. This muscular, tactile tail is an adaptation to the spider monkey's strictly arboreal lifestyle and grants the monkeys a fifth hand of sorts. Spider monkeys are highly agile; they are said to be second only to the gibbons in this respect.
Spider monkey arms are thin but very long. The legs are also long. While quadrupedal locomotion (using all four limbs) is common when on the ground, spider monkeys are one of the very few kinds of monkeys that do not rely on their arms to help them walk, but can stand and walk on two feet, often using the tail to hang onto something for support.
Spider monkey hands resemble their arms, being long and narrow, with thumbs absent or greatly reduced. The fingers are elongated and recurved.
An unusually long labia in females may be mistaken for a penis; its function is unclear.
A recent comparative intelligence comparison gives spider monkeys a value a little above gorillas, so it is reasonable to believe that spider monkeys are among the most intelligent New World monkeys (Leake and Dobson 2007).
At 107 grams, the spider monkey brain is actually twice the size of a howler monkey's of equivalent body size. This is thought to be a result of the spider monkeys' complex social system as well as their frugivorous diet, which consists primarily of ripe fruit from a wide variety (over 150 species) of plants and thus requires the monkeys to remember when and where fruit can be found. The slow rate of development in spider monkeys may also play a role, females giving birth once every three to four years. Spider monkeys may live for 20 years or more.
A spider monkey's diet consists of about 90 percent fruits and nuts (HZ 2007). They can live for long periods of time on only one or two different kinds of fruits and nuts. They eat the fruits of many big forest trees, and because it swallows fruits whole, the seeds are eventually passed out.
Russo and Augspurger (2002) found that spider monkeys of the species Ateles paniscus dispersed 84 percent of all dispersed seeds of Virola calophylla in a Peruvian tropical forest. Their effectiveness as seed dispersers showed up in terms of providing both high quantity dispersal (large number of seeds) and high quality dispersal (high per capita seed survival).
Spider monkeys are diurnal and most of the feeding happens between dawn and 10 a.m. After the morning feeding, the adults typically rest while the young play. Throughout the rest of the day they may feed infrequently until around 10 p.m. If their food is low they can resort to eating insects, bark, or rotting forest, and honey.
The spider monkey has a unique way of getting food because there is a lead female responsible for feeding. If she cannot find enough food for the entire group, they split into smaller ones to find food easier (ZS 2007).
Spider monkeys form loose groups of 15-25 individuals. During the day, spider monkey groups break up into smaller subgroups of two to eight individuals; this social structure ('fission-fusion') is found in only one other primate, the chimpanzee. The size of subgroups and the degree to which they will avoid each other during the day is determined by food competition and the risk of predation. Each group is closely associated with its territory (Gordon 2007).
Also less common in primates, females—rather than males—disperse at puberty to join new groups. Males tend to stick together for their whole life. Hence, males in a group are more likely to be related and have closer bonds than females. The strongest social bonds are formed between females and young offspring. Groups are thought to be directed by a lead female, who is responsible for planning an efficient route for the day's feeding activities.
Spider monkeys are diurnal and spend the night sleeping in carefully trees. Grooming is not as important to social interaction, due perhaps to a lack of thumbs.
The postures and stances of a spider monkey serve to communicate their intentions and observations. Examples include the postures of sexual receptivity or an attack posture. When a spider monkey sees a human coming near, it will bark loudly similar to a small dog. When a spider monkey is approached, it will climb to the end of the branch it is on and shake it vigorously in an attempt to scare the possible threat away. The animals shake the branches with their feet, hands, or a combination while hanging from their tail. They may also scratch their limbs or bodies with various parts of their hands and feet. Seated monkeys may sway and make noise. Male spider monkeys and occasionally adult females will growl menacingly at the approach of a human. If the animal's pursuer continues to advance, spider monkeys often will break off live or dead tree limb weighing up to 10 pounds and drop them towards the approaching person. The monkeys do not actually throw the branches but they will twist the branch causing it to fall closer to the threat. The natives of the area know very well of this risk. Spider monkeys will also defecate and urinate toward their observer (Carpenter 1935).
Spider monkeys mate year-round. The female monkey chooses a male from her group with whom to mate. Both male and female spider monkeys sniff their mates to check their readiness for copulation. This process is known as “anogenital sniffing.” On average, only one offspring at a time is produced from each female. The gestation period for spider monkeys ranges from 226 to 232 days.
A mother spider will carry a new born infant monkey around her belly for no more than the first month. After this, the young monkey travels on the lower back of the mother. The young monkey wraps its tail around its mother’s and grabs on tightly to its mother's midsection.
Mother spider monkeys are very protective of their young and are generally good mothers. They have been seen grabbing their young and putting them on their backs for protection as well as to help them navigate from tree to tree. They also aid in the crossing from tree to tree by pulling branches closer together to allow easier crossing of their more independent young. Mothers will also groom their young on occasion. For the first six to ten months of a young spider monkey’s life it relies completely on its mother (Carpenter 1935). Male spider monkeys have nothing to do with the raising of offspring.
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