Bird Statue

are NaN Objects in SS undefined. They are stone effigies of Loftwings that function similarly to the Owl Statues in. They can be found both in the overworld and inside dungeons. All of the Bird Statues on the surface are activated when Link examines the special statue near the Sealed Temple.

Location and Uses
Bird Statues primarily serve both as the save feature of SS - and as a gateway to The Sky. When in a dungeon, they cannot be used to return to the sky; instead, they are used to teleport Link out of the dungeon, similar to the Magic Mirror from or Ooccoo and Ooccoo Jr. from. If Link dies in his journey, he can continue it at these statues, saving him the trouble of exploring the land or dungeon again. Even if Link does not want to save a record of his quest, it is recommended to visit these statues so that he may mark their position on the map and dive to them later in the future.

Trivia

 * When Link is in the area of the Lanayru Desert containing the Temple of Time, the Bird Statue "Desert Entrance" is named "Lanayru Mine Entry" on the map, despite a different Bird Statue already having that name.

Nomenclature
See here for the translations of each surface Bird Statue location.