What does the mockingjay symbolize in The Hunger Games? I have muttations, rebellion, survival, beauty, mistakes, and communication. Can...

While agreeing wholeheartedly with all the above answers, I feel there is another aspect to the Mockingjay so far only briefly alluded to: communication.

One outstanding quality of the mockingjay are its beautiful and elaborate songs - and the fact that these mostly originate from other sources, which the birds pick up, transmit, and sometimes alter. Mockingjays cannot be abused for spying like their forefathers, the jabberjays, but they can still carry on a melody across wide distances, like an African drum. This in itself can serve as a means of communication: District 11 used it for warnings, Katniss and Rue to reassure one another; and the new Rebellion uses the Mockingjay, i.e. Katniss, as the unifying face and voice in the fight against the Capitol.

As the Mockingjay of the rebels, Katniss is turned into something like a leader-figure; but in the three books, she rarely really acts as a leader. She was not the one to call people to fight in the first place, but her individual (if defiant) actions in the arena of the 74th Hunger Games were amplified into a call for rebellion by the people in the districts (and President Snow himself). Even when she officially accepts the role of the Mockingjay, she is not the one who plans and designs the revolution but their broadcast face and mascot.

In reading the books, the degree to which Katniss's effect in the media is instrumentalised by all sides sometimes stung me. Like the real mockingjays, she is used to communicate to the rebels, and it is often the song of others that she transmits. However, while mockingjays are used, they cannot be fully controlled or instrumentalised: They choose which melodies to pick up; sometimes they remain silent; at other times, they sing of their own accord (e.g. to announce a Hovercraft). And so does Katniss: She decides what to communicate and how to communicate it; she gives the call for rebellion a voice and meaning of her own (often defying her supervisors and friends), and she lifts her voice against the plans and strategies of the rebel soldiers when she feels that their military strategies deny the very humanity they are all fighting for.

So, if Katniss becomes the Mockingjay, she does not assume the power of Leadership. But this does not mean she has no power. Hers is the subtle but incalculable power of the communicative act, the symbol itself.