Palm nuts of the genera Acrocomia and Attalea have shells that resist crushing far beyond what most birds can manage. The hyacinth macaw's bill is proportionally massive and, like other parrots, hinged at the skull so the upper mandible moves independently. The bird braces the nut against the lower mandible and applies a shearing rather than purely crushing action, often steadying the nut with its tongue.
Much of the work is done before the bird arrives. In the Pantanal, macaws frequently take nuts from cattle dung and from the ground beneath feeding sites, where the fibrous outer husk has already been stripped. Field studies have described this reliance on large grazers as a form of indirect feeding association.
The species is not simply a strong bill. Its dependence on a small number of palm species for food and on large hollow trees for nests makes it structurally fragile, and both nest trees and palms respond slowly to loss.