“Wheee... I'm a Red Feather! I help Kazooie fly, when she knows how!”
—A Red Feather, Banjo-Kazooie
Red Feathers are items that can be found in most levels throughout the Banjo-Kazooie series. They are used for Kazooie to gain altitude when flying. (Just taking off requires nothing but a Flight Pad.)
As well as this, Kazooie can use Red Feathers to perform the Beak Bomb while flying and the Talon Torpedo while swimming underwater with Banjo. However, performing these moves also costs red feathers (1 for Beak Bomb, 5 for Talon Torpedo). None of these moves can be used if Kazooie has no red feathers. However, the abundance of red feathers throughout both games makes running out of feathers a minor issue.
In Banjo-Kazooie, Banjo and Kazooie can initially carry only 50 feathers. However, speaking to the second Cheato hidden in Gruntilda's Lair grants the "REDFEATHERS" cheat, which, when typed on the Sandcastle floor in Treasure Trove Cove, will permanently increase the amount of Feathers they can carry to 100. Unlike other item capacities, the doubled limit stays in effect for Banjo-Tooie, meaning the "Feathers" cheat in said game doubles the capacity again to a whopping 200.
In Banjo-Kazooie: Nuts & Bolts, a Red Feather is seen in the box of Banjo and Kazooie's old moves which they receive at the end of the game.