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The Return of the Loudest Animal on Land

Story at-a-glance -

  • Conservation efforts have returned the native howler monkey to Tijuca forest in Rio de Janeiro after a century’s absence
  • Five howlers were reintroduced into the forest in September 2015, and several additional small groups will follow over the next few years
  • Howler monkeys are the largest of all New World monkeys, and the loudest land animals
  • Conservation efforts have also reintroduced cutias to Tijuca, and soon several other native animals will be returned to the forest as well

By Dr. Becker

It's been nearly 100 years since these ear-piercing primates perched in the treetops of Tijuca forest in Rio de Janeiro, but thanks to conservation efforts, the howler monkey is back in town. 

Tijuca is one of the largest urban forests in the world, but over the last century it has lost most of its wildlife to poaching and deforestation. But Brazilian scientists are determined to bring the forest back, and releasing native howler monkeys, also known as Alouattas, is an important step in the process.

As Fernando Fernandez, a scientist with the Federal University of Rio de Janeiro explains:

"The howlers disappeared more than 100 years ago. We decided to reintroduce them because it is a resistant species. They essentially eat leaves and fruits, so they are relatively easy to reintroduce."1

First Group of Howler Monkeys Reintroduced to Tijuca

The Tijuca forest, home to the Christ the Redeemer statue, covers 25 square miles and is just minutes from the neighborhoods of Rio.

The first group of five howler monkeys was released there in early September 2015 – a reintroduction that represents a significant milestone in a conservation program that began five years ago.

The monkeys, who were rescued from animal traffickers, are re-animating the forest with their trademark cries. In addition, their nutrient-dense feces gets moved across the forest floor by dung beetles, fertilizing soil, plants, and trees along the way.

Enresto Vivero de Castro, Tijuca administrator, hopes the forest can become a model for the rebuilding of wildlife species in other parts of the world.

Reintroduction Is a Necessarily Slow Process

Reintroduction of the Alouattas must be done with considerable care to avoid problems between incompatible groups of primates.

"The howler is the biggest monkey of the Atlantic Forest after the spider monkey," says Fernandez. "We got five individuals – three males and two females – and before releasing them we let them interact for five months in our research center.

"It's very important because the Alouattas form social groups and stay together in the forest," he said.2

The original group of five monkeys is now down to four. Chico, the dominant male of the group, kicked a younger male named Cesar out of the group. Cesar returned to the research center and will be released again in the future with a different group of howlers.

Other Primates, Humans Pose Threat to Howler Monkeys

The male howlers are identified by the bracelets they wear, and the females wear collars. So far, things seem to be going well in the forest.

"There was some concern when the group met some capuchin monkeys, which are more aggressive," said Fernandez. "But in the end there wasn't a problem." 3

Other monkeys aren't the only threat to the howlers. Human visitors to the forest can unintentionally kill the monkeys by feeding them, and dogs also pose a danger. Fernandez recommends that visitors to Tijuca keep their distance and avoid interacting with and feeding the howler monkeys.

"Watch and enjoy, because they are really cool," says Fernandez. "But from a distance."4

The current plan is to release new groups of howler monkeys to the forest over the next four years to create a population that is self-sustaining. A similar program has reintroduced cutias (a type of rodent), and there are plans to bring back native sloths, native boars, kinkajous, the endangered golden lion tamarin, and other native animals.

Seven Facts About Howler Monkeys

  1. Howlers are New World monkeys native to tropical Central and South America. They are the biggest of all the New World monkeys.
  2. The howler is named for his incredible vocal abilities, and is considered to be the loudest animal on land. When a group of howler monkeys starts screeching, typically at dawn or dusk, they can be heard up to three miles away.
  3. Male howlers have extra-large throats specially equipped to add volume to their calls. They often use louder calls to warn other monkeys away from their territory.
  4. Howler monkeys are omnivores. They average 22 to 36 inches in height, and weigh 15 to 22 pounds. Their tails measure 23 to 36 inches. The average lifespan of a howler in the wild is 15 to 20 years.
  5. They have a prehensile tail that is used to grasp or hold objects. It comes in quite in handy since howlers rarely touch the ground, preferring to stay up in trees, munching on leaves.
  6. Howlers have long, thick coats that are black, brown, or red. They also have beards.
  7. Most howler species live in groups of six to 15, which usually includes one to three adult males and several females. A group of howler monkeys is called a troop.