The secret behind red howler monkey's massive howl

Red howler monkey howling.

It begins as an eerie sound: “Rohooo, rohooo, rohooo.”

Then more voices joined in a moaning that built up to a long, vibrating crescendo like the roar of a strong blowing through a tunnel.

The cries waned for a moment, only to burst out with renewed force.

Finally the voices fall silent, and the echoes died away.

Gradually the buzzing of insects and the chirping of birds filled the jungle air again.

As you listen in, you wonder who are the performers of this hair-raising jungle chorus?

Then you discover five sturdily built red howler monkeys

Red howler monkey mighty howl

Picture of a howler monkey.

Red howler monkeys live high up in the trees, especially in the forests along the rivers, in groups of four to eight and sometimes more.

Usually the star performer is an old male standing almost three feet (0.9 m) tall.

His head, half of it consisting of a huge lower jaw, sat deep between his shoulders, giving him a hunched appearance.

The naked face contrasted with his orange-red body hair.

And a distinct yellowish-orange beard proclaimed his dignity and covered the source of all those spine-tingling roars—his swollen throat.

Why is it swollen?

The Jivaro Indians have an amusing answer:

‘One day,’ goes the story, ‘the howler showed the spider monkey how to break coconuts by pounding them together. When the spider monkey tried it, his thumbs got caught between the nuts and were lopped off. Determined to revenge his loss, he told the howler, “Don’t crack them at all. They taste much better when swallowed whole.” The howler followed his advice, but the coconut got stuck in his throat and left its mark on all his offspring, while the offspring of the spider monkey went without their thumbs.’ 

But when the Jivaro Indians shot a howler and looked inside its throat, there was no coconut.

What did they see?

A cup-shaped, hollow sound box of enlarged bones in the swollen throat.

This built-in echo chamber, the size of a lemon, is 25 times bigger in the male red howler monkey than the same body part in other similar-size monkeys, and it is unique among mammals.

As red howler monkey contracts the muscles of his chest and stomach, air is forced across an opening in this hollow sound box, and his voice is amplified so much that it can be heard over two miles (3.2 km) away.

Observers have found that on moonlit nights the howlers get “talkative” and do not mind skipping their night’s rest and disturbing yours.

But don’t think they will sleep in the next morning.

Just before sunrise they are up for a howling, and at the end of the day the chorus lines up again for their embarrassingly off-key serenade.

What can cause a red howler monkey to howl?

A clap of thunder or sudden downpour, a passing plane or even a flight of butterflies will get them howling.

You wonder: Do they ever take a break?

They do, they select a barren branch, wrapped their tail around it, and stretched out belly down.

With long arms and legs dangling loose, they doze off.