Arctic Warbler

The Arctic warbler is a strongly migratory leaf warbler that breeds in birch or mixed birch forest near water across Fennoscandia and northern Eurasia, with an additional breeding foothold in Alaska. The entire population winters in Southeast Asia, giving this insect-eating species one of the longest migrations undertaken by an Old World insectivorous bird. Records outside its normal passage and wintering range require care because closely related cryptic species were formerly included within the same complex. (Wikipedia, general species account)