Birds, especially those that spend much of their lives on the ground, make some of the most unusual sounds of the tropical rainforest.

Because only a small amount of sunlight can filter through to the rainforest floor, many rainforest animals have evolved to favor auditory over visual communication

Cassowary

New Guinea's largest endemic bird, the cassowary, cannot fly at all.

The cassowary is more often heard than seen, announcing its presence by a loud, deep booming which changes to a harsh cackling and croaking.

It is a huge bird, and may stand as tall as a human being and weigh about 100 pounds (45kg).

Despite their size, cassowaries are light on their feet and can disappear into forest thickets easily in order to escape their enemies.

Cassowaries are dangerous to human beings when they are cornered. They attack by kicking powerfully, with the inner toe thrust outward. They can slash open a soft-bodied vertebrate with a single kick.

The cassowary's closest relative is the Australian emu.

Trumpeter

The calls of male trumpeters resonate throughout the Amazonian forest.

These birds, which are similar in size to domestic chickens, live in large flocks deep within the forest.

Although they can fly, and build their nests in tree forks and other safe places above the ground, trumpeters feed almost entirely on the ground, searching for fruits, berries, seeds and insects.

If danger threatens, they run quickly to the safety of a dense thicket.

The females look exactly like the males, and the sex of an individual can be confirmed only by observing its behavior. The male takes the lead in courtship.

Pitta

The pitta, which resides in Asia, Australia and Africa, can be identified by its distinct whistling, trilling and rolling calls.

Pittas search for small invertebrates, as well as vertebrates, on the rainforest floor, carrying snails to anvil stones to crack them. They also eat seeds, fruits and berries.

They are smal and stocky and have brightly colored plumage.

Rainforest animals are often brilliantly colored. Males' coloration plays an important role in courtship displays. The dark environment makes camouflage unnecessary.