[Case 17.] 
[Case 17.] 
32 BIRD GALLERY. 
Grouse, or entirely feathered as in the Capercaillies and Black Grouse, 
etc., and never armed with spurs. The toes are either covered with 
feathers as in the Ptarmigan, or naked and pectinate, that is to say with 
a series of horny comb-like processes on each side, as in the Capercaillies, 
Black Grouse, etc. 
In no group of birds are the seasonal changes of plumage more 
interesting and peculiar than in the Willow-Grouse, Red Grouse, and 
the various kinds of Ptarmigan, and therefore worthy of special notice- 
The seasonal changes are attained in three different ways:—(1) By 
moult. (2) By gradual change of pattern in the old feathers without 
a moult. (3) By the wearing off of the tips of the feathers. The quills 
and tail-feathers are only renewed once a year at the general autumn- 
moult, which is always the most complete. 
Wild hybrids between some of the species of this family appear to be 
more common than among any other group of birds, possibly because 
they attract greater attention. In many Grouse the females which have 
become barren from old age or from injury to the ovary assume a 
plumage more or less resembling that of the male, and examples of this 
peculiarity are exhibited in the groups of Capercaillie and Black Grouse. 
More rarely the reverse obtains, and examples of males assuming the 
female plumage are met with. 
The Capercaillies (Tetrao), of which four European and Asiatic species 
are known, are the largest members of the family. ‘The common Caper- 
eaillie (7. urogallus) (169), inhabiting the pine forests of Europe and 
Northern and Central Asia, is common in some of the eastern counties 
of Scotland. Hybrids between this species and the Black Grouse (170) 
are by no means rare, the male offspring, of which a fine example is 
shown, being remarkably handsome birds with a violet gloss on the breast. 
In the American bare-toed Grouse belonging to the genera Dendra- 
gapus (111), Tympanuchus (118), Centrocercus (174), and Pediwcetes 
(175, 176), of all of which examples are exhibited, the males are provided 
with a pair of inflatable air-sacs situated one on each side of the neck. 
These are not visible except when the bird is excited or showing off to 
the females, but at such times they can be blown out like a bladder 
and enable him to produce deep booming sounds which may be heard 
at a great distance. The stomach of the Sage-Grouse (Centrocercus 
urophasianus) (174), a native of the sage-brush plains of Western 
North America, differs from that of other game-birds in being soft and 
membranous, very different from the muscular gizzard found in all the 
allied forms. As its name implies, this species is seldom found far 
from the tracts of Sage-brush (Artemisia), the leaves of which form its 
principal food, and during the winter months, when it eats little else, its 
flesh is unfit for the table. The Prairie Hen (Tympanuchus americanus) 
