Planes don't fly radically differently than birds. Birds can flap their wings because they're light and small. Birds don't fly by flapping their wings, they flap their wings to fly. The flapping is to gain and maintain height but beyond that they use the same principle to stay afloat. Birds expend massive amounts of energy to flap too and eat a lot of food to compensate. Large predatory birds try their best to glide as much as possible as a consequence. To carry a human, you need a proportionally larger machine and the square-cubed law would stop us from being able to flap plane size wings. Aside from that, birds and planes fly on the same Bernoulli's Principle of fluid motion and to compensate for being unable to take off from rest with wings, we made engines that provide thrust.
If AGI doesn't take the form of human-ish intelligence, then we'd never know it was intelligence. This means that the target is always a "visible" human like intelligence and that was gained through evolution and millions of years of experimentation and records. It will most certainly not take that long for human-like intelligence to form given our current progress but we would not recognise anything else.