Biologist Greg Budney sets out well before dawn in the Peten region of Guatemala to record a chorus of howler monkeys as they wake.
"I love this sound," he says. "It's one of the great sounds of tropical forests: the voice of howler monkeys."
The biggest of the New World monkeys, black howlers are found in tropical regions of Central and South America. They're up to 3 feet tall, not counting the tail, and spend most of their time in trees.
When several get together to roar, you can hear them from three miles away.
"The males, in particular, have a large throat sac, which they expand when they vocalize, so they're a pretty formidable-looking primate," says Budney.
The morning bellows of howlers are as much a hallmark of tropical forests as the toucan's calls.