Though howler monkeys are named for the noise they make, they sound much more like a lion then a wolf when they 'howl.' They use their gruff roars to lay claim to territory - and can be heard up to two miles away. Unlike most other monkeys, they are slow-moving and leaf-eating. Scientists believe that toxins in the leaves they eat make them lethargic. But since they never have to go far to look for leaves, they don't need to be as quick and mobile as their fruit and nut-eating cousins.

Photo: The Belize Zoo