beak

A beak is the hard pointed mouth of a bird. A curved beak, open its beak, a beak full of worms.

Bill is the alternative word, and there is no consistent rule — birds of prey have beaks and ducks have bills, mostly by custom. The shape tells you the diet almost exactly: a hooked beak tears meat, a thin one probes for insects, a heavy conical one crushes seeds. Note that Darwin's finches are the standard example, and that beak in British school slang also means a headmaster or a magistrate.