Jabberjay

Jabberjays are a type of bird that were created in Capitol labs to spy on enemies and rebels of the Capitol. Jabberjays had the ability to memorize and repeat entire human conversations, and were used to gather words from the rebels. Once the people in the districts realized how their private conversations were being transmitted, they used the jabberjays to feed lies to the Capitol. The Capitol therefore ceased using the jabberjays and abandoned them to die off in the wild, but they didn't die off. The male jabberjays bred with female mockingbirds to create mockingjays, which were able to repeat both human melodies and birdsong. They were considered a slap in the face to the Capitol, because it had failed to foresee that possibility.

Catching Fire
By the 75th Hunger Games, the Capitol had replenished the jabberjay population. In the 4:00 section of the arena, the birds mimicked the screams of the tribute's loved ones, luring in Finnick Odair and Katniss Everdeen. A transparent barrier kept them inside, forcing them to listen to the tortuously realistic shrieks of Annie Cresta, Primrose Everdeen, and Gale Hawthorne. Katniss and Finnick worried that the Capitol had tortured their loved ones to produce screams for the jabberjays to memorize, but they soon realized that the Capitol had used digital or mechanical means to warp their voices into screams.

Appearance
They are said to be visibly similar to their mockingjay descendants, and passed on their black feathers and crest.