But this time they wouldn't have to evolve it from scratch. It's not hard to imagine a bird such as an ostrich evolving into a flight capable bird, especially if there were no existing flighted birds to compete with. They have elaborate feathered wings, so the biggest change needed is probably just to be smaller. Probably 99.9% of the DNA necessary for flight is already there, it just needs to be regulated a bit differently. This would even be true in birds like kiwis or emus, whose wings are much smaller and vestigial.