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."
Ο πελεκάνος τρώει ψωμι = The pelican is eating bread. Ο πελεκάνος τρώει το ψωμί = the pelican is eating the bread
Surely a simple sentence like this, without any context, needs to be translated straightforwardly. Enough of the technical analysis of a short statement like this however correct the arguments.