I know Accelerate hasn’t even been released yet, and the public doesn’t know much about how the game will function aside from it being a Mario Kart clone, but I thought I would put my two cents in.
In Mario Kart: Double Dash for the Gamecube, every character has a Special Item that only they can obtain. Peach and Daisy’s Special Item is the Heart, which creates two hearts that circle around their kart. When an item such as a Banana or Green/Red Shell collides with a heart, both disappear and the item the heart blocked is given to the heart’s user.
My suggestion is to have the Birb Shield do this with items such as the Bowling Balls, consuming the shield when an item hits it but giving the blocked item to the shield’s user.