420. Acanthopneuste borealis.
The Arctic Willow-Warbler.
Phyllopneuste borealis, Blas. Xaum. 1858, p. 313; Hume, S. F. iv, p. 290. Phylloscopus borealis (Blas.), Hume Dav. S. F. vi, p. 352; Hume, Cat. no. 556 bis; Oates, S. F. x, p. 222 ; id. B. B. i, p. 77; Seebohm, Cat. B. M. v, p. 40; Hume, S. F. xi, p. 218.
Coloration. Upper plumage olive-green, lighter on the rump; wings brown, the outer webs edged with olive-green ; wing-coverts brown on the inner and olive-green on the outer webs ; the median and greater coverts with yellowish-white tips, forming two bars ; tail brown, the outer webs edged with olive-green ; a broad and well-defined eye-streak, reaching to the nape, yellowish white; lores brown; ear-coverts olive, mingled with yellowish ; under plumage white, suffused with yellow; under wing-coverts and axillaries pale yellow.
As the summer goes on the wing-bars get worn away and the upper one is sometimes absent. The lower plumage gets whiter and the upper plumage duller. After the autumn moult the wing-bars are very conspicuous and the underparts become suffused with deeper yellow.
Upper mandible dark brown, the edges and tip yellow; gape and basal half of the lower mandible orange-yellow, terminal half dusky; mouth bright orange-yellow; iris dark brown; legs flesh-colour, tinged with yellow ; claws yellowish horn-colour.
Length 4.8 ; tail 2 ; wing 2.7 ; tarsus .8 ; bill from gape .68 ; the second primary is intermediate in Length between the fifth and sixth, and is sometimes equal to the sixth; the first primary is very small, measuring from .3 to .45 inch in Length.
Distribution. A fairly common winter visitor to Southern Pegu and Tenasserim, arriving about the middle of September. Hume met with it at Aimole on the eastern hills of Manipur in the middle of April. It has been procured in the South Andaman, from which locality 1 have examined two specimens.
It has a wide range in winter through South-eastern Asia, and it summers in Northern Asia.