The actual bread it is referring to has not been specified, therefore "The pelican is eating bread" should be the correct answer. Eg. if we want to say "the bread" we would have to say something like "The pelican is eating the bread which was thrown to it."
to psomi is the bread, not just bread. It is the indefinite article ( enas, mia, ena ) which is often not needed in Greek. The definite article (o, h, to) is just as important in Greek as it is in English.