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. 



[Case 17.] The Capercaillies (Tetrad), of which four European and Asiatic species 

 are known, are the largest members of the family. The common Caper- 

 caillie (T. 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. 



[Case 17.] In the American bare-toed Grouse belonging to the genera Dendra- 

 gapus (171), Tympanuchus (173), Centrocercus (174), and Pedicecetes 

 (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) 



