Any of several species of slow-moving tropical American monkey s (genus Alouatta ) noted for their roaring cries, which carry over a distance of 2–3 mi (3–5 km).
Five widely distributed species are the largest New World monkeys, generally reaching lengths of 16–28 in. (40–70 cm), excluding the 20–30-in. (50–75-cm) tail. Howlers are stoutly built and bearded, with a hunched appearance and a thickly furred, prehensile tail. Their hair is long and thick and, depending on the species, black, brown, or red. Howlers live in groups in territories mapped out by howling matches with neighbouring clans. They feed primarily on leaves.