Clay licks, or collpas, are exposed riverbank faces where parrots including scarlet macaws land in numbers each morning and scrape mouthfuls of soil. The behaviour is geographically patchy: it is common in the western Amazon and largely absent from much of the eastern basin and Central America.
Two explanations have competed. The older one holds that clay particles bind plant toxins in seeds the birds eat, allowing a broader diet. The newer one notes that the layers the birds actually select are not the most adsorbent, but are relatively high in sodium, an element that is scarce in the interior of the continent and drops off with distance from the Atlantic.
The geographical pattern favours sodium: lick use rises where soil and rainfall sodium are lowest. Detoxification has not been ruled out entirely and the two are not exclusive, but treating clay eating as simply an antidote overstates a case the field evidence does not carry.