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 (Sangster et al. 2002, Parkin 2003):

• 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 (Helbig et al. 1995).

The species is migratory, wintering in sub-Saharan Africa. It is a rare vagrant in Northern Europe.

Western Bonelli's Warbler is a small passerine bird, found in forest and woodland. 4-6 eggs are laid in a nest on the ground. Like most warblers, Western Bonelli's is insectivorous.

It is a small warbler. 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.(Helb et al. 1982)

This bird is named after the Italian ornithologist Franco Andrea Bonelli.

References

• Helb, H.-W.; Bergmann, H.-H. & Martens, J. (1982): Acoustic differences between populations of western and eastern Bonelli's Warblers (Phylloscopus bonelli, Sylviidae). Cellular and Molecular Life Sciences 38(3): 356–357. (HTML abstract)

• Helbig, A. J.; Seibold, I.; Martens, J. & Wink, M. (1995): Genetic differentiation and phylogenetic relationships of Bonelli's Warbler Phylloscopus bonelli and Green Warbler P. nitidus. J. Avian Biol. 26: 139–153.

• Parkin, David T. (2003): Birding and DNA: species for the new millennium. Bird Study 50(3): 223–242. HTML abstract

• Sangster, George; Knox, Alan G.; Helbig, Andreas J. & Parkin, David T. (2002): Taxonomic recommendations for European birds. Ibis 144(1): 153–159. PDF fulltext