There are birds that go far longer than typical aeroplane flight times without a single flap of their wings either using thermal, ridge, or other sources of lift. Are these flying birds? I've shared thermals with eagles flying the same circles, neither one of us flapping our wings but making minor adjustments for the same goal.

An albatross might be able to go days flying without a single wing flap and no vertical sources of lift by using dynamic soaring in the wind gradient at the surface of the ocean. Perhaps that's something only birds can do. Except the glider pilot Ingo Renner once found an amazing shear layer at 300m altitude and stayed there with dynamic soaring. Remote control gliders use the lee of ridgelines to approach Mach 1 with dynamic soaring.

Perhaps what defines a bird that flies as opposed to a plane is that a bird produces thrust by flapping its wings? Even an Albatross must flap its wings if it has to take-off from water. Maybe we could add that the flapping is driven by animal muscles? But then is the human powered ornithopter Snowbird a bird that flies as opposed to a plane?

Of course this is all ridiculous because everyone knows what you mean when you refer to a bird or plane. We have other ways to definitively identify the difference rather than their mode of flight. It's trickier when I'm asked if an AI is conscious. There is no definitive base-line to fall back on to decide if this is a conscious or conscious-less thinker.