These vocal primates are the biggest of all the New World monkeys. Unlike Old World monkeys, howlers and other New World species have wide, side-opening nostrils and no pads on their rumps. Howlers also boast a prehensile tail. They can use this tail as an extra arm to grip or even hang from branches—no Old World monkeys have such a tail. A gripping tail is particularly helpful to howler monkeys because they rarely descend to the ground. They prefer to stay aloft, munching on the leaves that make up most of their diet. Howler monkeys are also known to occasionally raid birds' nests and chicken coops and consume the eggs.
Howler monkeys have beards and long, thick hair which may be black, brown, or red. The red howler species is the most common, but it is often targeted by hunters eager for bushmeat. Other species of howler monkey may be critically endangered over sections of their ranges.