Identification
Dusky Naumann’s Thrush is an Asian vagrant (breeds in Siberia central from eastwards). The bird recalls Redwing in structure but is substantially larger with a stouter bill and relatively long tail. The two subspecies appear distinctly different in the field and are best considered separately.
The medium-size Dusky Naumann’s Thrush adult male bird is dull dark brown above with blackish feather centers, giving the mottled appearance (with wear, upperparts appear blacker). Hence, becoming blacker on the crown and ear-coverts which contrast with the conspicuous white supercilium and throat, the latter extending across the side of the neck to form a half-collar as in Redwing.
Moreover, the feathers of the rump and upper tail coverts are broadly fringed rufous, and the wings are largely rufous-chestnut. The whitish underparts are heavily mottled and scaled blackish, forming ill-defined breast bands that contrast with a cleaner throat. The underwing is almost entirely rufous.
Unlikely to be confused, but occasional variant individuals lacking rufous-chestnut in wings could perhaps be confused with female Black-throated Thrush. Adult females’ birds and 1st-years are usually duller overall, with duller rufous-buff areas in wings, and are less intensely scaled and mottled than adult males. These birds are most likely to be confused with smaller redwings.
This also shows paler areas on the wing, prominent pale supercilium and collar, and diffuse breast streaking forming a chest band. But Redwing has rufous flanks, is browner above, has rich buff ground color to the breast and buff wash to the supercilium, and has a darker rufous underwing (duller rufous in Dusky).
Therefore, some Dusky have rufous scaling mixed with black on underparts, especially on flanks, and others are intermediate between Dusky and Naumann’s. All kinds of apparent intermediate plumages can be seen.
Dusky Naumann’s Thrush (nominate race)! Upperparts lack the blackish mottling of dusky, being greyish-brown overall, while underpart markings are rufous-chestnut instead of black, often being more diffuse and thus producing almost wholly rufous breast and flanks, mixed with whitish scaling in fresh plumage.
Some black speckling and scaling are usually present at the sides of the throat and on the breast, and rufous scaling is present on the upper parts. The bright rufous outer tail feathers are obvious in flight, and less striking on the ground (were partially obscured by browner central feathers).
The throat and supercilium are off-white, washed rusty-buff. The upper wing lacks strong rufous tones, but the underwing is darker rufous. Adult females and 1st years average duller, but the pattern and color are distinctive and not matched by any other thrush of our region.
Although the red-throated race of Dark-throated Thrush also has a bright rufous tail. Both forms feed more in the open than most other Asian thrushes, perching freely on tops of bushes and trees and feeding on the ground in the manner of Fieldfare.
Sex and Age
As already discussed under the Identification section. Some adult male Dusky is duller than usual, so sexing is not always straightforward. However, adult females generally have less blackish feather centers above and below, often have more distinct malar stripes and primary coverts appear duller, less strongly rufous, and have less distinct, brownish (rather than blackish) tips.
Adult Dusky Naumann’s Thrush is often hard to sex, but females average duller below (especially on the throat, which is often paler), tend to show more distinct malar stripes, and usually have less rufous scapulars. The juveniles of both forms are heavily pale-spotted above and dark-spotted below.
The first-years may have more distinct whitish or pale buff tips to greater coverts than adults. 1st-year male Dusky usually resembles adult males in having blacker feather centers on both upper parts and underparts, but primary coverts are closer to those of adult females (although dark tips are blacker and more distinct).
Some 1st-year female Dusky Naumann’s Thrush may be separated by obvious dark spotting on the breast (and sometimes flanks), but many are inseparable from 1st-year males.
Voice of Dusky Naumann’s Thrush
The Dusky Naumann’s Thrush simple flute calls include a harsh chattering ‘chak-chakchak’ of alarm, recalling Fieldfare, a shrill, wheezy ‘spirr’, recalling Common Starling, a loud, shrill, nasal ‘cheeh-cheeh’ and many other high-pitched calls. The whistling song, unlikely to be heard, consists of several clear, descending notes followed by a faint Twitter and recalls Redwing.
Taxonomy
Intermediates between Dusky and Naumann’s Thrushes are not infrequent. But as the area of hybridization appears to be quite limited, Dusky Thrush is sometimes accorded full species status as T. eunomus.
