The hyacinth macaw has a curved beak which is strong enough to crack hard nuts, including Brazil nuts, macadamia nuts and even coconuts.
They cannot crack open acuri nuts though, and wait for them to pass through the digestive system of cattle before eating them.
(Taken from 25 of the Worlds Most Endangered Animals)
Hyacinth macaws image by Geoff Gallice cc2.0
The hyacinth macaw is also mentioned in:
Top 10 Fun Facts About Parrots