The Arctic warbler (Phylloscopus borealis) – 13cm is a widespread leaf warbler in birchor mixed birch forest near water throughout its breeding range in Fennoscandiaand northern Asia. It has established a foothold in North America, breeding in Alaska. This warbler is strongly migratory; the entire population winters in southeast Asia. It therefore has one of the longest migrations of any Old World insectivorous bird.
It traditionally included populations that breed in Kamchatka, the Kuril Islandsand Japan, but genetic and vocal evidence strongly suggested these should be treated as separate species, and are all now considered distinct with the Kamchatka leaf warbler in Kamchatka, Hokkaido and the Kuril Islands, and the Japanese leaf warbler in Japan (except Hokkaido).
The nest is on the ground in a low shrub. Like most Old World warblers, this small passerine is insectivorous. In Labuan Island this leaf warbler may be spotted during their wintering migration season around September till April the next year.