Why Do Macaws Eat Clay? Inside the Amazon Clay Licks

What is a clay lick?

A clay lick is an exposed bank of soil, usually where a river has cut into an old terrace, that animals visit to eat the earth. In southeastern Peru, these banks can be tens of meters high and hundreds of meters long. The birds do not eat just any soil: they return to particular layers, often a single band only a meter or two thick, while ignoring the layers above and below.

The most famous sites lie in Tambopata National Reserve and Manu National Park in the Peruvian department of Madre de Dios. Large and small licks are also found in eastern Ecuador, northern Bolivia and western Brazil. Eating soil in this way is called geophagy, from the Greek for “earth eating”.

The sodium hypothesis: the leading explanation

Sodium is essential for nerves, muscles and the balance of body fluids, but plants need very little of it, so a diet of seeds and fruit is naturally low in sodium. Near the coast, sea spray and rain bring sodium inland, but in the western Amazon, more than 1,000 km (620 mi) from the Atlantic, it is in short supply.

Several lines of evidence point to sodium as the main reason parrots eat clay:

• Chosen soils are salty. Analyses at Peruvian licks have repeatedly found that the soil layers parrots prefer contain more sodium than the layers they avoid.
• Geography fits. A study of clay licks across South America by Lee and colleagues (2010) found that parrot geophagy is concentrated in the western Amazon and becomes more common the farther a site is from the ocean, exactly where sodium is scarcest.
• Timing fits. Clay lick use peaks during the parrots’ breeding season, when parents need extra minerals and are feeding fast-growing chicks. Researchers in Tambopata have found soil in the food that macaw parents regurgitate to their nestlings.

The detoxification hypothesis

The older and still popular explanation is that clay protects parrots from poisons. Many of the seeds and unripe fruits that macaws eat contain alkaloids, tannins and other defensive chemicals. Clay minerals carry negative charges that can bind some of these compounds in the gut.

In laboratory experiments with soil from a Peruvian lick, Gilardi and colleagues (1999) showed that the clay could bind a test alkaloid and reduce how much reached the bloodstream of captive parrots, and that it helped protect the lining of the gut.

The problem is geography. Parrots in Central America and the eastern Amazon also eat plenty of toxic seeds, yet they rarely visit clay licks. If detoxification were the main driver, clay eating would be common wherever parrots eat bitter food. Most researchers now see toxin binding as a possible extra benefit rather than the primary reason.

Which parrots visit clay licks?

More than a dozen parrot species use the licks of southeastern Peru. Regular visitors include:

• Large macaws: scarlet macaws, red-and-green macaws and blue-and-yellow macaws.
• Smaller macaws: chestnut-fronted and red-bellied macaws.
• Parrots and parakeets: mealy amazons, blue-headed parrots, white-bellied parrots, and dusky-headed and cobalt-winged parakeets.

Each species tends to use particular parts of a bank and its own time of day. Smaller parrots often feed first, while the big macaws may wait in the treetops for an hour or more before descending.

Clay eating is not limited to the Americas. In the forests of Central Africa, African gray parrots gather in open forest clearings to eat soil, and sulphur-crested cockatoos have been recorded eating clay in New Guinea.

Why the spectacle is so cautious

Clay licks are dangerous places. A bare bank offers no cover, and birds of prey such as hawks and hawk-eagles watch for parrots on the ground. Before landing, the flock perches in nearby trees, calling and watching, sometimes for a long time. A single alarm call can send hundreds of birds into the air at once in a burst of red, blue and green.

This wariness is also why disturbance matters. Boats, loud voices or people standing in the open can keep birds off a lick for a whole morning. Well-run lodges use hides set back across the river, so visitors can watch without changing the birds’ behavior.

Rain also changes the pattern. Parrots tend to avoid licks during and after heavy rain, and the busiest days are usually clear mornings in the breeding season.

Do macaws need clay to survive?

Not everywhere. Scarlet macaws in Central America live and breed without regular clay licks, probably because their food and environment provide enough sodium closer to the sea. In the western Amazon, however, licks seem to be an important resource, and protecting them, and the forests around them, is part of macaw conservation.

Clay is only one part of a macaw’s diet. The birds still rely on a powerful bill to open hard seeds and unripe fruit, as explained in How strong is a macaw’s beak? For other Amazon wildlife, see our list of rainforest animals.