The Arctic warbler (Phylloscopus borealis) is a widespread leaf warbler in birch or mixed birch forest near water throughout its breeding range in Fennoscandia and 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. The nest is on the ground in a low shrub. Like most Old World warblers, this small passerine is insectivorous.