Birdo is a possibly gender-confused creature of a dinosaur-type species that first appeared in Super Mario Bros. 2. A Birdo makes a small appearance in Cooking with Mario and Bowser 2! as one of the customers at the rivals' new restaurant. In it, Birdo is just a quick cameo who sits on one of the tables. "She" appears in Gmod form.
According to theories, Birdo is a transexual because "she" says "she" is a girl in the Ninendo games, but the Nintendo guidebook says Birdo is a boy.
Picture of Birdo (official).