I've wondered about this. Birds use a different structure, the pallium, in place of the sheet of cortical stacks we call the cerebral cortex. The pallium is more compact, not requiring more brain mass to support more area and so more stacks - so comparing cranial volume doesn't work.

My wondering was more along the lines of "welp, if birds are that smart for that volume, why is there no evidence that the dinosaurs (who had considerably more cranial capacity) *did* anything, not even cave drawings, in 160 million years?" Hominids have been around less than 3M, about a half a percent of the time, and hey, look at us - we're in process of destroying the planet. Whatever comes next will have a hard time missing that. :-)