Ridgway on the Plumage of Gyrfalcons. 
93 
detailed description of the perfect adult dress of this dark form of 
the Gyrfalcon has, to my knowledge, been published. 
Adult — Above continuous plumbeous-slate, interrupted by a some- 
what Y-shaped patch of pale buff, or buffy white, longitudinal markings 
on the nape ; the head perfectly uniform, the feathers of the dorsal-region 
and wings showing paler borders and transverse spots, there being about 
one pair (one on each web) of the latter on the exposed portion of each 
feather; remiges and primary coverts plumbeous-slate, without any spots, 
but with paler edges. Rump and upper tail-coverts more bluish than the 
back, and with distinct transverse spots and bars of light bluish-plumbeous, 
these bars regular and sharply defined on the upper tail-coverts, where 
they average, like the darker ones, about .25 of an inch in width; the 
shafts of these feathers conspicuously darker than the ground-color. Tail 
similar in colors and markings to the upper coverts, there -being about 
eight or nine bands on that portion of the tail not concealed by the coverts ; 
the light bars more or less mottled, finely, with darker ; tip of the tail, 
rather narrowly, whitish. Ground-color of the lower parts creamy white, 
or pale cream-color, changing to light plumbeous on the thighs and anal 
region, the crissum tinged with the same. Chin and throat washed with 
grayish, and streaked (not sharply) with dusky; whole jugulum and breast 
thickly marked with sharply defined longitudinal stripes of blackish slate, 
these markings gradually assuming on the abdomen the form of tear- 
shaped and oval spots ; flanks with wide transverse spots of blackish slate, 
some of the spots more or less cordate; tibial plumes thickly barred with 
transverse, somewhat cordate spots of deep plumbeous, the shafts con- 
spicuously blackish ; anal region similarly but more densely marked ; 
lower tail-coverts very regularly barred with deep plumbeous, the bars 
sharply defined, somewhat crescentic, and about .30 of an inch in width, 
or a little narrower than the lighter ones. Lining of the wing irregularly 
spotted with dark slate and pale cream-color, in nearly equal proportion ; 
under surface of the quills silvery plumbeous, faintly and irregularly mot- 
tled with pale creamy, but not showing any tendency to form transverse 
or ovate spots. Wing, 14.00-14.40 ; tail, 8.40-9.00 ; culmen, .90 ; tarsus, 
2.25-2.35 (bare portion about .80) ; middle toe, 1.90. 
Adult 9 • — Much darker than the and of a more sooty shade. No 
trace of the light nuchal markings ; spots of the back, etc., smaller and 
more scattered ; rump and upper tail-coverts slaty-plumbeous (about like 
the back of the <£), the former with small scattered spots, the latter with 
narrow bars of light grayish or dirty whitish. Tail brownish slate, nar- 
rowly tipped with whitish, and marked with incomplete or interrupted 
narrow bands of light mottled grayish ; none of these bars, except the 
subterminal ones, reach the shaft ; they are narrower and wider apart than 
those of the about eight showing beyond the upper coverts on the 
middle rectrices. Chin and throat as in the but remaining lower 
