They had seen several howler monkeys already on their trip.

At least eight families of howler monkeys have been identified.

The sound set off a band of howler monkeys on the left shore.

Across the river, high up in the trees, we saw a troop of black howler monkeys.

Same goes for the howler monkeys, who howled too late.

Somewhere a group of howler monkeys shrieked out their presence.

The air soon became muggy and filled with the sounds of howler monkeys.

In the evenings she can hear the howler monkeys and watch their young swinging from one branch to another.

Somewhere in the distance, a howler monkey screeches into the night.

Listen for the roar of howler monkeys at the cave entrance.