He can borrow animal's ability like flying from birds but how is he flying without birds or turning into a bird?

@redwingx: Because it's magic.

I see. Imo it would have been cooler if he had wings when he borrowed a bird's ability to fly and that way he wouldn't be Beastboy 2.0 either.

@redwingx: Yeah, but it's not that he change his body per se. His power is that he is part of a sort of giant telepathic connection of all animals in the universe. The closer he is to a certain animal, the easier it is to get the power. So its more of a sort of telepathic power than one that change his body.

... yeah, Animal Man is one of the more weirder heroes...

Originally Buddy tapped into the morphogenic field and borrowed the abilities from nearby animals. This was an ability given to him by aliens. Its since been retconned that he's an elemental avatar and taps into the Red. Also recently able to use the abilities of space animals. And actually he does take on animal physical traits since his power up in the New 52.

That's really cool, still wish he had always animal physical traits tho