The thing about definitions is that they are only intended as succinct heuristic statements that serve as a clue to a pattern of usage in a speech community. They aren't the same as word meanings, and they often tend to focus on distinctive aspects of a concept that are unique to the word sense being identified. Meanings themselves are a vast web of associations that are ultimately grounded in the way our bodies interact with physical reality. That is, they depend on filtering through the senses (touch, sight, smell, taste, hearing). You can't fully define a meaning, since it is a kind of network of associations that are more or less central to the concept. Any definition of a human being is just going to identify a piece of the whole, not the whole meaning itself.
What I'm trying to say here is that there is no perfect definition of any physical object, because the meaning is comprised of many different properties. Generally speaking, birds can fly, but there are a number of flightless bird species. Swans tend to be white, but there are also black swans. Different language systems will tend to parse the same reality in slightly different ways, depending on how speakers tend to interact with their environments. If one never sees a black swan, then whiteness can become a distinctive property for defining swans.