These transient varieties account for 60 % or 250 of the total number of the island's bird species. The remaining 150 species are residents having made their way to this island abode due to the climatic and geologic forces that helped shape the eventual nature and location of the land.
有些留鳥也有移棲的行為，但是它們採「垂直遷徙」：冬天從寒冷的高山上往下飛，搬到海拔較低、氣候較暖的山坡上住，並不飛離島外。雖然僅佔五分之二，留鳥種類也有一百五十種之多，這在一般海島來講，並不常見。