Birdie is a Birdo and Boshi's companion in Mario & Luigi: Rivals Quest, helping him with his schemes. Similarly to how Boshi seems like a rival to Yoshi, Birdie could be considered a rival of sorts to Birdo, although it's unknown if they know each other.
Birdie, as a Birdo, is not too different from others in her species. She is a yellow Birdo with three dark orange spots on her left cheek and a white stomach, as well as dark orange spikes on her back. She also wears an orange ribbon on her head and has a pink ponytail.
Birdie first appears bugging some Toads in the Gritzy Badlands, alongside Boshi. The Wario Bros. run away, leaving the Mario Bros. to fight her and Boshi. The Mario Bros. defeat Birdie and Boshi, who run away after their defeat.