When you think of monkeys, you think of playful animals; the ones that swing from branch to branch; the curious and cheerful animals that even stealthily steal food from humans naively walking through trails. But the Mantled Howler Monkey (Alouatta palliata) does not really fit this description. They do have arboreal and diurnal habits but they are pretty sedentary and move about very little. Their diet consists mainly of fresh leaves but they also eat fruit. They are for the most part social animals and can live in groups of up to 20 individuals; although usually they are seen in small groups and within each group there is a dominant male. However, what makes these monkeys different is exactly as its name implies: its howl. The males have a highly developed hyoid bone, which allows their throat to be a soundboard that amplifies sounds. Their howl can be heard more than 8km away!