Flying like a Bird is Hard

Our friends at Festo have done a lot of cool stuff.  Inflatable architecture.  Pneumatic muscle.  But this is really incredible.  Its hard to fly like a bird for lots of reasons, but mostly its power to weight.  Watching Boston Dynamics' terrifyingly determined, gasoline powered dog-bot you get some idea of how much power it takes just to walk.  It takes a chainsaw's worth!

But festo's bird has somehow gotten enough juice in a light weight enough package to fly.  Amazing!  A chain saw is a pretty lightweight power source.  What's in the bird?