Baby, I'm howlin' for you. Male howler monkeys make deep and boisterous calls to attract mates, but the deepest-pitched songs may come at cost: the size of their testicles. A new study in the journal ...

Howler monkeys. From their Central and South American rainforest home, they produce some of the loudest animal calls in the world. They’re about the size of an adult cocker spaniel, but they can sound ...