The Bowser's Kingdom Power Moon 50 - Small Bird in Bowser's Castle is one of the Power Moons you can find at Bowser's Kingdom. You can find this Power Moon in Quadrant E1.

The Bowser's Kingdom Power Moon 39 - Sphynx Over Bowser's Castle is one of the Power Moons located at Bowser's Kingdom, but only after you have completed the story.