Zoo officials said police tracked down Kelli using a signal from a microchip planted on the bird. She got the medical all-clear and was returned to her penguin partner, Mick.
Police said the thieves climbed over a security fence into an enclosure housing about a dozen Humboldt penguins and picked Kelli for reasons unknown.
Dublin Zoo has been targeted by annoying pranks before. In 2008, its switchboard was overwhelmed by callers asking to speak to Rory Lyon, G. Raffe and Ana Conda.