Mangabeys are some of the rarest and endangered monkeys on Earth. These large forest dwellers are found only in Africa. They look somewhat like guenons but are bigger. Local people call some of them "the ones with the thin waist" or "four-eyed monkeys" because some mangabey species have bright white eyelids. Black mangabeys have long, grayish-brown whiskers that almost cover their ears and a high crest on their head—a pointy hairdo! Adult male mangabeys also make a sound that biologists call a whoop-gobble. The whoop gets the attention of other mangabeys in the area; the gobble tells everyone who and where he is. This unique call may be heard for a distance of up to 1,000 yards (1 kilometer).