Detailed Instructions: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
Problem:Is there a single word to describe birds that can fly? Am I struggling to think of a word because the default notion of a bird is that it can fly? So we generally only need to differentiate the ones that can't fly. I've seen the term 'winged' in a few google searches, but to my mind an ostrich is winged, but it is also flightless. I guess I'm looking for the word you'd put into this blank: Penguins are flightless because they cannot fly. Ostriches are flightless because they cannot fly. Pigeons are ____ because they can fly.
Solution:
I think you can just use flying to describe them; flying birds sounds perfectly normal and isn't a tautology, nor does it only apply to birds in the air, cf. the title of the Wikipedia article 'Flying and gliding animals'. It's obviously an awkward choice for your example sentence, where another option, volant, could be used instead: 2: flying or capable of flying (source: Merriam-Webster)