Eastern Bonelli’s Warbler

Overview

The eastern Bonelli's warbler (Phylloscopus orientalis), sometimes known as the Balkan warbler, is a warbler in the leaf warbler genus Phylloscopus. It was formerly regarded as the eastern subspecies of a wider "Bonelli's warbler" species, but as a result of modern taxonomic developments, they are now usually considered to be two species:

Western Bonelli's warbler, Phylloscopus bonelli, which breeds in southwest Europe and north Africa
Eastern Bonelli's warbler, Phylloscopus orientalis, which breeds in southeast Europe and Asia Minor
The breeding ranges of the two species do not overlap; while their appearance and songs are very similar, the calls are completely different (see below). They also show marked difference in mtDNA sequence.
The species is migratory, wintering in sub-Saharan Africa.

Summary from Wikipedia, available under CC BY-SA 4.0.