Monkeys in U.S. zoos

What counts as a monkey

"Monkey" is a common name rather than a single scientific group. It covers the simians, the primate branch that also includes apes, minus the apes themselves. Lemurs, lorises, galagos and tarsiers are primates but not monkeys. Monkeys range in size from the pygmy marmoset, at just over 100 g (3.5 oz), to the male mandrill, which can weigh up to 36 kg (79 lb).

Many monkey species live in trees, and most are active during the day. Some spend most of their time on the ground, such as the baboons. The hamadryas baboon lives in harems of one male and up to ten females that combine into clans, bands and troops sharing sleeping cliffs.

New World or Old World: how to tell

New World monkeys, from Central and South America, reached South America tens of millions of years ago, probably by crossing the ocean. Their nostrils face sideways, and most have long tails. In the howler and spider monkey family, and in the capuchins, the tail is prehensile and can grip branches. The black-handed spider monkey uses its tail as a fifth limb, and the black howler monkey has a bare patch on the underside of its tail that improves grip.

Old World monkeys, from Africa and Asia, have nostrils that point downward and tails that cannot grip, or no visible tail at all. They also see color the way humans do, while New World monkeys vary. The black-and-white colobus eats mostly leaves, digested in a large, multi-chambered stomach, and has only a vestigial thumb. The patas monkey of the African savanna is the fastest runner of any primate, at up to 55 km/h (34 mph).

Tools, troops and tamarins

Some monkeys solve problems in striking ways. The capuchin monkey is the only New World primate that regularly uses tools in the wild, cracking nuts with stone hammers, a practice dating back at least 3,000 years. The Japanese macaque, the northernmost non-human primate, is known for bathing in hot springs in winter.

Tamarins and marmosets are small monkeys, and the pygmy marmoset is the smallest of all. The golden lion tamarin, with its fiery mane, weighs around 620 g (1.37 lb) and comes from Brazil's Atlantic coastal forests, and the cotton-top tamarin from a small area of northwestern Colombia.

Conservation pressures

Primates as a whole are in trouble: about 60% of species are threatened with extinction, including 36% in South and Central America, 37% in Africa and 73% in Asia. In Central and South America, forest fragmentation and hunting are the two main problems, and large unbroken forests are now rare in Central America. Monkeys that raid crops are often persecuted, which can work against efforts to protect endangered species.

The cotton-top tamarin is listed as Critically Endangered, with fewer than 6,000 left in the wild. The golden lion tamarin shows what recovery can look like: from a few hundred animals it has grown to roughly 4,800, helped by the reintroduction of zoo-born tamarins and reforestation that reconnects isolated patches of habitat.