Dusky warbler 
(Phylloscopus fuscatus)

The dusky warbler (Phylloscopus fuscatus) is a leaf warbler which breeds in the east Palearctic.
This warbler is strongly migratory and winters in South Asia and South-east Asia, sometimes occurs in North America in Alaska, and has also occurred in California.

Leaf warblers were formerly included in the Old World warbler family but are now considered to belong to the family Phylloscopidae, introduced in 2006.
The name Phylloscopus combines the Ancient Greek phullon meaning "leaf" and skopos meaning "seeker" (from skopeo, "to watch").
The specific fuscatus is from Latin fuscus "dark".