There are many idioms that involve birds. It would help to know which idiom you're asking about. Here are a few examples:
Common idioms with birds:
* "A bird in the hand is worth two in the bush." This means it's better to be content with what you have than to risk losing it by trying to get something more.
* "To kill two birds with one stone." This means to achieve two goals with a single action.
* "Early bird gets the worm." This idiom suggests that those who are up early and ready to work are likely to be successful.
* "To be a bird of a feather." This means to be similar to someone in personality, interests, or background.
* "To feel like a bird in a gilded cage." This means to feel trapped and restricted, even though one's surroundings are outwardly luxurious.
* "To let the cat out of the bag." This means to reveal a secret. (The idiom actually uses a cat, but often "the cat" is replaced with a "bird" in this context).
Please tell me which idiom you're interested in, and I can explain its meaning in more detail!