Oystercatcher
The oystercatcher has the heaviest bill (= beak) of any living wader. They have "resource polymorphism": they have some different beak types, and each type is used for a different kind of feeding. Unusually, the polymorphism is not genetically determined. It seems individuals are able to change their beak to suit their food. They do, of course, inherit an ability to adapt their feeding behaviour.