Kazooie is a large, red female bird who is referred to as a "Red-Crested Breegull". She is Banjo's closest companion and lifelong friend, although their personalities are quite different from each other's. Whereas Banjo is polite and friendly, Kazooie is loud, sarcastic and rude. Kazooie does not hesitate to make crass statements about even the most imposing figures that the duo encounter, much to Banjo's dismay. Although Banjo often finds himself apologizing for Kazooie's remarks, they almost always find themselves embroiled in dangerous situations simply due to Kazooie's inability to keep quiet. Kazooie has the ability to lay and spit out many different kinds of eggs, from ordinary blue ones, to giant spotted ones that hatch miniature robotic duplicates of herself. She can also spread her wings and fly, carrying Banjo with her, although doing so causes her to lose feathers. In Banjo-Kazooie: Nuts & Bolts she loses all of her moves and instead uses a magic wrench. As her name suggests, she plays the kazoo.
Source: Wikipedia, "Banjo-Kazooie (series)", available under the CC-BY-SA License.