Special topic
Report of Dark-throated Thrush ? (Turdus ruficollis) ?
In the week of April 8, a strange looking thrush was reported from a local birdwatcher in a sub-urban park. After a few days, when the photo of individual was circulated, it was considered as an immature race ruficollis of Dark-throated Thrush. During the weekend of April 13 and 14, hundreds of birders visited in the park. Although I tried to avoid the "rush hour", there were still more than 50 people when I visited on April 15. The following is my observation report of the unidentified thrush.
Size & shape: The thrush is approximately same size with
the common Dusky (T. naumanni) and Pale (T. pallidus) Thrush. So, its length is estimated approximately
25 cm. The shape is slightly different
from Dusky Thrush. The unidentified thrush
tends to keep more standing style when it
is on the ground. On the other hand, similar
Dusky (Naumann's) Thrush tends to keep slightly
horizontal position (See the photo below
for the comparison: left is Naumann's Thrush).
The thrush's tail and neck seem to be slightly
longer. Accordingly Svensson et. al (1999), Dark-throated Thrush describes that
"Fieldfare shaped" while Dusky
Thrush is described as "Shape of Song
Thrush". Although unfortunately this
description does not make me sense much,
it is enough to understand at least the shape
is different among two species.
Identification: There are three species of thrushes which
have clear eye-brow in far east Asia. They
are: 
Siberian Ground Thrush, Dusky Thrush and
Eye-browed Thrush. In Central Asia, in addition
to these species, Dark-throated Thrush, Redwing
and Fieldfare. Since Siberian Ground Thrush
has distinctive black plumage in male and
dark brown with scaly pattern in female,
it is doubtlessly not the one. Both male
and female Eye-browed Thrush has rustic brown
on belly with no stripe nor streak. Redwing
has distinctive reddish brown flank with
bold streak on throat, belly and flank. Also,
it is too large for Redwing. Fieldfare has
brown mantle and scaly side which are not
found in the individual. Therefore, there
are two possible species for this strange
looking thrush. As a race naumanni of Dusky
Thrush, its rustic brown parts are too small.
In the photo, the individual has mottled
rufous (not rustic) brown on the throat (see
photo above) and
whitish belly with faint grey streaking on
lower breast and flank (see photo right
with comparison of Naumman's Thrush: left),
which is a distinctive feature of race ruficollis
of Dark-throated Thrush. As other features,
the individual shows: evenly grey-brown
above; clear whitish supercilium; heavy brackish malar
stripe and throat; grey rump(see photo below);
and dark greysh tail. Unlikely Naumann's
Thursh, it did not have broad rusty brown
outer tail feathers (though it has rufous
fringes on the most outer tail feather).
With these features, the individual is considered
as race ruficollis of Dark-throated Thrush.
Aging: From the photos, it is easily recognised
that the individual is at least not adult
male. As most of the field guide books show,
even adult female has rufous supercilium.
Since the individual does not have rufous
supercilium, it is therefore assumed as 1st
year individual. Illustration of 1st year
individuals is very 
variable in the field guide books. Accordingly Robson (2000) and Alström and Colston (1991), 1st year female has whitish supercilium
and is described as "more streaked and mottled". With this information, the individual is
assumed as 1st year female. Actually, a photo
of Japanese field guide book "Nihon-no-tori
550" shows 1st winter male which has
clear rufous supercillium. However, the throat
seems too bright rufous for 1st year
female. Therefore, further reading and reference
are needed to prove the assumption.
Call: not heard.
The individual was observed by April 18 in the same park. Dark-throated Thrush is rare winter or passage migrant in Japan. This record is probably the first record in Osaka Prefecture (although there is an unaccepted record before) and even first record in western Honshu.
Since there are some discussions about this individual (some people consider this individual as "Dusky Thrush" while some others consider "1st year male" T. r. ruficollis, your comments are welcomed!!
Reference:
Colströn, Peter et.al (1991). A Field Guide to the Rare Birds of Britain and Europe. Harper Collins, U.K.
Grimmet, Richard et. al. (1999). Birds of the Indian Subcontinent. Christopher Helm Ltd., U.K.
Hirozo, Maki & Toshikazu, Onishi (2000). A Photographic Guide to the Birds of Japan. Heibonsha, Tokyo
Jonsson, Lars (1992). Birds of Europe with North Africa and the Middle East. Christopher Helm Ltd., U.K.
MacKinnon, John & Phillipps, Karen (2000). A Field Guide to the Birds of China. Oxford University Press, U.K.
Svensson, Lars, et.al. (1999). Bird Guide: The Most Complete Field Guide to the Birds of Britain and Europe. Harper Collins, U.K.