The Western Bonelli's warbler is a "warbler" in the leaf warbler genus Phylloscopus. It was formerly regarded as the western subspecies of a wider "Bonelli's warbler" species, but as a result of modern taxonomic developments, this species is now usually considered to be two species:
- Western Bonelli's warbler, Phylloscopus bonelli, which breeds in south west Europe and north Africa
- Eastern Bonelli's warbler, Phylloscopus orientalis, which breeds in south east 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 genus name Phylloscopus is from Ancient Greek phullon, "leaf", and skopos, "seeker" (from skopeo, "to watch"). The English name and the specific bonelli are for the Italian ornithologist Franco Andrea Bonelli.
The adult has a plain grey-green back, green-toned rump and wings and whitish underparts. The bill is small and pointed and the legs brown. The sexes are identical, as with most warblers.
The western Bonelli's warbler has a browner tinge to the upperparts than eastern Bonelli's warbler; the latter sometimes has a greenish tinge instead. The song is a fast monotone trill, only slightly different from eastern Bonelli's, and also some similarity to wood warbler. The call of the western Bonelli's warbler is a disyllabic hu-it, differing from that of eastern which is a completely different hard chup, reminiscent of a crossbill or a house sparrow
The first record for Romania was in 31 august 2021 near the Black sea cost.