That works for flight, but not for intelligence. We can define what “flight” means, but we can’t do that for “intelligence”. Unless by “intelligent” you really mean “appears to be behaving like a human”.
Intelligence is a higher order trait so harder to describe, but it is still a discernible trait. Roughly speaking, intelligence is the ability to achieve an objective through modeling scenarios in order to determine more optimal behavior.
Intelligence across species shares common characteristics even between dolphins, apes and birds which all evolved it independently.
Intelligence across species shares common characteristics even between dolphins, apes and birds which all evolved it independently.