A mysterious bird given to Castor Oyl by his uncle Lubry Kent, Bernice dodged Castor's every attempt to rid himself of her, having grown attached to her master. He then found out about her true powers: she would grant luck to anyone who rubbed her feathers. So Castor set sail to Dice Island, where a legendary casino stood, meeting and hiring Popeye to man the ship he bought. During the trip both Popeye and Castor obtained luck from rubbing Bernice, and millions were won upon arriving at the casino. On the way back Popeye, having been shot multiple times by the evil casino manager, kept rubbing Bernice's feathers for "luck" and eventually recovered. It is unclear if his miraculous recovery owed to Bernice's powers or to his formidable constitution, which he was not yet aware of.
Bernice would remain at Castor's side until, during a trip to Africa, she met a male of her species and chose to leave with him.
The character is portrayed differently in the 1960 animated series, where she appears as a talking magical animal with a human-like personality, known as the "Wiffle Bird" who would occasionally appear to grant wishes or make amazing things happen. Despite being referred to as female, she had a clearly male voice. This would remain her only screen portrayal.