The Amazon rainforest boasts more primate species than any other habitat on earth. Yet the largest primates,
the apes, are absent from South America. The reason is that apes evolved in Africa and never had the chance
to spread to South America. Scientists believe that New World and Old World primates split away from each
other around 35 million years ago.
Small monkeys are in the Cebidae family (see Small monkeys), whereas
larger Amazon monkeys previously assigned to this family are now included in three other families, the
Atelidae (spider monkeys, woolly monkeys and howler monkeys), Pitheciidae (titis, saki monkeys and
uakaris) and Aotidae (owl or night monkeys).
The total number of primate species varies according to taxonomic revisions, nowadays based
primarily on DNA evidence. In addition, new species might be found. In September 2004, a new species of titi
monkey was discovered in Madidi National Park in the Bolivian Amazon. The discovery received widespread
publicity because the discoverer, British biologist Robert Wallace, decided to auction the right to name the
monkey in order to raise money for the park. Even Ellen DeGeneres bid for the right, which was eventually
won by a commercial corporation with a bid of $650,000.
APPEARANCE
The sakis and uakaris (Pitheciidae) weigh 2-4 kg, about the same as a small dog. Their tails are
non-prehensile (do not grasp branches) and often give them away as it is easy to spot the bushy tails
hanging below a branch. They have long hair, quite untidy, perhaps as a protection against ants that they
must frequently encounter on their forays among the treetops. These monkeys are dark in color and often hard
to spot as they are not particularly active. Night monkeys (Aotidae) are small, weighing about 0.75 to 1.25
kg. They have huge eyes, rimmed in white to give them a spectacled appearance. At night, the eyes reflect
back a reddish-orange color. The third family of large Amazon monkeys, the Atelidae, includes our idea of a
typical rainforest monkey; such as the howler monkeys, spider monkeys and woolly monkeys. Howler monkeys are
large, and heavy set with striking beards, coming in a range of colors from pale yellow to black. Spider and
woolly monkeys are graceful, slim-built and are colored black to dark brown. The woolly monkey has dense fur
whereas the spider monkey's fur is coarser.
The heaviest of these monkeys, weighing up to 15 kg, all have prehensile tails, whereas the lighter species
do not. The prehensile tail acts as a fifth limb, able to support the weight of the body, giving rise to the
iconic image of a rainforest monkey hanging by its tail. The tip of the tail has a bare patch of skin on the
underside that helps it grip the branch. It feels as though someone is coiling their finger around you. In
appearance these species vary from the punk-rocker spider monkeys to the appropriately named monk saki which
indeed looks like a monk! However, within species vary in color between populations separated by wide rivers
or mountains, suggesting that not much interbreeding occurs between widely separated groups. This process of
differentiation between populations is believed to be the initial stage of speciation, when a new species
arises from an existing one.
HABITAT AND DISTRIBUTION
The families of large Amazon monkeys are variously distributed across the Amazon, limited only by the
altiplano of the Andes mountains. Where there is forest there are monkeys. That said, some species are
highly restricted in range, such that this group includes among the rarest Amazon mammals. In particular,
the white uakari is limited to a small area of varzea forest in the upper Amazon south of Iquitos, and the
yellow-tailed woolly monkey (Lagothrix flavicauda)is found only in montane cloud forests of the Peruvian Andes at elevations of
1700 to 2500 meters. Some species of titi monkeys also have very small ranges. At the other end of the
scale, the night monkey (Aotus sp.) is found almost across the entire extent of lowland rainforest.
Presumably, its nocturnal habits are one aspect of its niche that enables it to avoid competition with
other primate species as its range overlaps considerably with the similarly widespread capuchin monkey
(Cebus apella). Of the saki monkeys, the monk saki (Pithecia monachus) is the most
widespread, whereas the buffy saki (P. albicans) is locally common but found only in Brazil between
the Purus and Juarua rivers.
FEEDING AND DIET
All the cebid monkeys are fruit eaters, although insects are an important part of the diet for most species,
and vegetation is significant in others. The sakis and uakaris have dentition that appears to be specialized
to split open unripe fruits whose seeds form the main part of their diet. Capuchins on the other hand feed
on ripe fruits, with invertebrates and small vertebrates often on the menu. The largest monkeys, such as the
the howler monkeys, spider and woolly monkeys include a greater proportion of leafy vegetation in their
diets.
BREEDING
Only a single young is born, which is then carried by the mother. Among smaller monogamous species such as
the dusky titi (Callicebus moloch) the father takes up this duty). The family structure varies. Among
the saki monkeys, the group is dominated by a single breeding female who gives birth two to three years.
Combined with the low number of young born, this makes the species slow to recover following population
declines. Another factor is the late age of breeding. For example, the woolly monkeys (Lagothrix
lagothricha) first breed at age 6 to 8 and give birth every other year. The spider monkey (Ateles
paniscus) breeds at about 4 years old but thereafter give birth only every three to four years.
CONSERVATION
Some cebid monkeys are in pretty good shape from a conservation standpoint. The night monkey is among the
commonest species around human settlements as it adapts to secondary forest and more to the point is hard to
hunt, being active mainly at night. Large monkeys are more intensively hunted because they are a more
efficient prey item for the hunter; that is, they yield more meat per shot. For that reason, a number of
species are at risk of extinction, particularly those with small geographic ranges.
Monkeys are critical contributors to the rainforest ecosystem. Being the main dispersers of seeds for
hundreds of tree species, especially lianas and the tall canopy trees, they subtly but profoundly affect the
composition of woody plant species—the forest as we experience it. When monkeys are removed by hunting,
the particular suite of species in an area will inevitably change, with unknown domino effects for other
plant and animal species all around.
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