This is a typical
leaf warbler in appearance, grayish-green above and off-white below. The single wing bar found in the southern and western populations distinguishes them from most similar
species (except
Arctic warbler P. borealis). It is slightly smaller than that species and has a thinner bill, without a dark tip to the lower
mandible. A
latitude-based analysis of wintering birds indicated that more northerly
P. trochiloides are smaller, i.e. this species does not seem to follow
Bergmann's rule. Its song is a high jerky trill, in some populations containing a sequence of down- and more rarely up
slurred notes. It breeds in
lowland deciduous or mixed forest; non-breeding birds in the warmer parts of its range may move to
montane habitat in summer. Individuals from southeast of the
Himalayas are for example quite often seen in
Bhutan during the hot months, typically in
humid Bhutan Fir (
Abies densa) forest up to about 3,800 meters
ASL or more, but they do not breed there and return again to the adjacent
subtropical lowlands in winter. The
nest is on the ground in low
shrub. Like its relatives, this small
passerine is
insectivorous.
Subspecies and evolution around
Himalayas.Yellow:
P. t. trochiloidesOrange:
P. t. obscuratusRed:
P. t. plumbeitarsusgreen:
P. t. ludlowiBlue:
P. t. viridanusP. t. nitidus of the
Caucasus is not shown. It has a number of
subspecies, of which
P. t . viridianus is the most familiar in
Europe. As it seems, it is a
ring species, with populations diverging east- and westwards of the
Tibetan Plateau, later meeting on the northern side. Their relationships are therefore fairly confusing: •
Eastern group: greenish warblers •
Phylloscopus trochiloides trochiloides:
greenish warbler • Southern rim of the
Himalaya eastwards from
Nepal into W
China. • Dusky greyish green above, often traces of second wing bar. •
Phylloscopus trochiloides obscuratus:
dull-green warbler • Intermediate between
trochiloides and
two-barred warbler. •
Gansu and surroundings, China. •
Phylloscopus trochiloides ludlowi •
Western group: green warblers •
Phylloscopus trochiloides viridanus:
western greenish warbler • Breeds Western Siberia to north-east Europe; at east of range south to NW India. • Dull green above, with yellowish
supercilium, throat, breast and faint wing bar. The groups' origin lies probably in the
Himalayan region, where
trochiloides is found. This
taxon is close to the
parapatric obscuratus, and to
plumbeitarsus which is geographically separated from
obscuratus; they all can (and in the case of the former two do naturally)
hybridize.
P. t. plumbeitarsus is often split as distinct
species, as it does not hybridize with
viridianus in the narrow zone in the western
Sayan Mountains where their ranges overlap. But
phylogenetically, the western
taxa are even more distinct. However, there is some
gene flow between
trochiloides and
viridianus also, with their
hybrids being especially common in
Baltistan; which are now considered as a distinct subspecies
ludlowi. The
green warbler P. nitidus, now considered as a distinct species, is a mountain isolate that diverged from ancestral
viridianus.
Song structure differs mainly between greenish warbler and
two-barred warbler, which was formerly considered conspecific. The former has a fairly uniform, long, and warbling song. Around the Himalayas, song structure is similar, but songs are generally shorter. Two-barred warbler, on the other hand, has a long song that can be clearly divided into a warbling part, followed by a series of up- and downslurred notes. The songs of
obscuratus and
ludlowi, are short, but contain the downslur elements too; in the latter, they uniquely appear at the start of the song. ==Footnotes==