Forest Speaks

Howler Monkeys

Howler monkeys make a big sound, but they are not big animals. Weight: 4.8-7.7 kg Body length: 40.5-55.5 cm

The howling sound is produced by resonating air that is forced out through a large hollow bone in the male's throat.




Here's how it sounds!

Howler monkeys typically howl

At dawn

Just before it rains

When threatened by predators

When another group is nearby


Monkey killers:

Bot fly larvae develop in the skin, forming large lesions. The larvae do not kill the monkeys, but may further weaken animals that are already suffering from malnutrition.

Screw worms, the larvae of another type of fly, may enter empty bot fly lesions or wounds, and almost always kill their host. In the 1950's, the number of monkeys dropped to only 250, maybe as a result of a yellow fever epidemic. This disease, spread by mosquitos, affects humans, too.

Chapman photos of Claudia


In 1927, Donato, the Island caretaker, captured a baby howler.

"Claudia" lived in a cage, loved to play on ropes, and to eat the leaves of a tree growing there. She howled in despair when she heard passing troops of monkeys go by, and after a year she "died of a broken heart."

"What do monkeys eat?"

Ficus insipida: Frutos y hojas jóvenes

Spondias mombin: frutas

Cecropia Insignis: inflorescencias, frutas y hojas jóvenes

Click on images to enlarge

Howlers eat fruit, leaves and flowers.

Food is scarce during the middle part of the rainy season (July and August), and during the transition from winter to summer (December).

How many howler monkeys are there?

Dawn census: In 1977, 25 volunteers went to different points on the island. They counted a total of 65 troops howling. Since there are about 19 monkeys per troop, they calculated that there were more than 1200 howler monkeys on Barro Colorado Island.

The number of monkeys has not changed very much during the last twenty years.