"Funny birds and something of a slap in the face to the" oppressive government which had bred the all male Jabberjay as information gathering homing birds. The rebels used them to spread miss-information and the government abandoned the birds "to die off in the wild. Only they didn't die off. Instead, the jabberjays mated with female mockingbirds, creating a whole new species that could replicate both bird whistles and human melodies."
A symbolic icon worn by Katniss Everdeen, first as a symbol of protection and a totem from her home district.
The origins of the Mocking-jay pin differ in the book and the movie.
Collins, Suzanne (2009-09-01). The Hunger Games (pp. 42-44). Scholastic Books.
Katniss meets a girl that claims to have special mockingjay friends that will carry messages for her.