470 BULLETIN 50, UNITED STATES NATIONAL MUSEUM 



terminal edge of pale fuscous to liair brown; lesser and median upper 

 wing coverts, alula, lesser under wing coverts, lower back, rump, tail, 

 upper and under tail coverts, flanks, and thighs pure white; super- 

 ciliary stripe from above the bare loreal area to behind the eye, cheeks, 

 auriculars, chin, middle of throat, and sides of neck, except for the 

 band mentioned above, chaetura drab to fuscous-black with obsolete 

 paler shaft stripes; lower throat paler fuscous, the feathers with 

 elongated pale olive-bufF to creamy white tips; breast, sides, and 

 abdomen mummy brown to rather light fuscous; median and greater 

 under wing coverts fuscous-black; iris cream to light yellow; cere and 

 bare orbital area, tarsi, and toes, intense golden yellow; bill bright 

 yellow with a definite orange tinge; claws horny whitish, blackish only 

 basally. 



Immature (sexes apparently alike, but no definitely sexed birds of 

 this stage seen, the differences in size alone suggesting the presence of 

 both sexes). — Similar to the adult, but with no whitish or pale olive- 

 buff on the forehead, crown, nape, and throat; no white on the wing 

 coverts, which are dark fuscous; the inner secondaries and the scapulars 

 much mottled or blotched with white, sometimes chiefly white, broadly 

 tipped and otherwise mottled with fuscous; all the remiges white at 

 base, this being very conspicuous on the under sm'face; lower back, 

 rump, upper tail coverts, and tail white broadly tipped and sub- 

 terminally mottled Avith fuscous, the mottling very extensive covering 

 most of the feathers on the lower back, rump, and, to a lesser extent, 

 the upper tail coverts; most of the feathers of the upperparts -with 

 white bases which occasionally show through; the same also true for 

 those of the underparts; thighs and flanlis dark fuscous like the abdo- 

 men; under tail coverts fuscous mottled and blotched with dirty 

 white. ^^ 



Juvenal. — Similar to the immature plumage, but with the general 

 tone of the plumage darker; almost fuscous-black, rectrices much 

 mottled with fuscous and basally of this color. 



Natal down. — At first said to be pure white all over; later (as seen 

 in one bird in post-natal molt) smoky light drab down on the body 

 and legs, slightly darker on the head. 



Adult maZe.— Wing, 600-610; tail 320; culmen from cere 63-65; 

 tarsus 98-99; middle toe without claw 74 mm.^^ 



3' It seems (but is not definitely established) that the birds become more whitish 

 on the lower back, rump, upper and under tail coverts, and tail, and less so on the 

 bases of the body feathers with successive immature plumages, so that the transi- 

 tion from the juvenal to the adult stage is relatively gradual. 



" Two specimens from Kamchatka. Three unsexed birds from the same place, 

 probably males, have the following dimensions: Wing, 585, 590, 605; tail, 300, 

 313, 315; culmen from cere 66, 66, 67; tarsus 97, 97; middle toe without claw 67, 

 75 mm. 



