What does the idiom a little bird told you mean?

The idiom "a little bird told you" means someone told you something in secret. It's used to playfully avoid revealing the source of information, often implying that the information is gossip or a rumour.

For example:

* "How did you know about the surprise party?"

* "Oh, a little bird told me."

The idiom suggests that the speaker has a secret source of information, but they're not willing to disclose it. It can also be used humorously to imply that the speaker knows something that others don't, even if they're not entirely sure where they got the information.