Yup, you can't punch a bird. You can however, throw a rock at it. And to add to reasons, psychic is weak to dark, bug and ghost. Three things that can strike fear in the mind. --- Gordon Ramsay, the Mr Resetti of cooking
Anyone that says punching birds needs to get a clue. Birds have nothing to do with the flying type. Bird type was just a mistranslation.
Flying type should be interpreted as the wind type. Punching wind is not very effective..you try it. Now flying resisting fighting makes sense. --- If you don't like me, it's natural. Mortals are jealous of the superior.