Howler monkeys are the largest monkeys in Central America. Adults can weigh up to 10 kilograms, about the same as a big house cat. They live in groups of around fifteen animals, spending almost all of their time up in the tree canopy where they eat leaves, fruit, and flowers.
The extraordinary call comes from a special hollow bone in the throat called a hyoid bone. The hollow space inside it amplifies the sound, a bit like how the inside of a guitar makes the strings sound louder. Males and females both call, but the males are loudest. The call tells other groups of howler monkeys exactly where they are, so the two groups can avoid each other without fighting.
Howler monkeys have a prehensile tail — that means the tail is strong and flexible enough to grip branches, acting like a fifth hand. They can hang by their tail alone while their arms and legs are free. Baby howler monkeys spend their first months clinging to their mother's back as she moves through the forest.
In Guatemala, howler monkeys live in the forests of Petén, near Tikal, and in other lowland jungle areas. They play an important role in the forest because, like the quetzal, they eat fruit and later deposit the seeds elsewhere in their droppings, helping trees to grow in new places.