Obviously, it wasn't always called Bird Island.
What did Chamorros call it before the English name became prominent?
Isletan Maigo' Fåhang.
A list of Saipan place names
The fåhang is known in English as a "noddy tern." These birds favor coastal cliffs and small rocks or islets along the shore.
Isleta means islet, or small island. The word is borrowed from Spanish.
Maigo' means "sleep" or "asleep" and it probably refers to the fåhang using this rock to rest and sleep at.
Apparently the Japanese, who ruled Saipan from 1914 to 1944, had their own name for the island. Tsukimi, which means "moon viewing."