Capes

On the first level of the second "section" of the island (The one with Yoshi), you will notice turtles flying through the level wearing capes. Some of them will be wearing yellow capes, others wearing, uh, rainbow-ey capes. Hit the rainbow-ey ones on the back with a normal jump (Not spin jump) and you will unveil a feather, because apparently thats where magic flying capes come from.