58 THE SPECIES— ITS TAXONOMY, RANGE, BIOLOGY, & ECONOMIC IMPORTANCE 



But, while these represent the extremes of the variation, there are all manner of intergrada- 

 tions. The matter is further complicated by the intermating of members of different sub- 

 species in areas where both are found. Thus one often encounters birds which, although 

 basically gray, exhibit a suffusion of buffy or pale rufous. Similarly, the tails of red-phase 

 birds range from pale straw-color to a bright rufous. The degree of fine transverse barring in 

 the tail-feathers also varies, being least prominent in decidedly rufous specimens. 



That the color phase exhibited by a bird may not always be constant was discovered at the 

 Research Center when several birds, which had tended toward the red type to begin with, 

 came to more nearly resemble the gray type following subsequent moults. 



The occurrence of albinism has been recorded but it is rare. In this connection, it may be 

 noted that artificially propagated birds sometimes produce white feathers as a result df nutri- 

 tional disturbances. 



So far as is known, melanism has not been observed. In 1928. iiowcver, Allen'' reported that, 

 after moulting, the feathers of certain diseased birds exhibited an increased amount of black 

 pigment. 



ANATOMY* 



Existing species of animal life have gradually developed, through innumerable eons of 

 lime, from much more primitive forms. Structure is the jirimary basis for tracing these 

 lines of evolution, as well as for determining the relationships of contemporarv groups. 



In the Appendix"^ is included a comprehensive account of the anatonn of the ruffed grouse, 

 of which the following is a brief synopsis. 



In common with other fowl-like birds^ this species has a generalized structure, as shown by 

 the presence of two carotid arteries and a gall bladder, and the absence of a penis. The intes- 

 tines are looped in a primitive manner within tlie body cavity. 



A notable specialization is a cutaneous muscle lying beneath each tract of ruff feathers, the 

 contraction of which causes these feathers to rise away from the neck. 



In its skeleton, the grouse is essentially similar to the barnyard fowl liut sniall<'r llnougli- 

 out. In comparison with other members of the Tetraonidae, it is the lightest built. Most 

 of the differences, however, are merely of degree. Perhaps the most ])ron(iunced is its higher 

 pelvis. Of interest is the fact that there is greater variation between the genera with respect 

 to the pelvis and the vertebral cohunn than tlie lioncs of the extremities. 



Likewise, the arrangement of the muscles appears to be quite similar to that of other mem- 

 bers of the family as well as the chicken and quail. Present knowledge of this subject, however, 

 is very limited regarding most of the other species in the group. 



The syrinx or "voice box" (whiih is highly developed among the singing birds) is of the 

 primitive tracheo-bronchial type and is adapted to only rudimentary notes*. 



Respiration is carried on by means of lungs as in mammals. In addition, and connected 

 to them by bronchial tubes, is a system of membranous bladders or air sacs ffive in all) 

 which serve to increase the buoyancy of the bird's body. Also associated willi this arrange- 

 ment are the hollow interiors of the larger bones of the body. 



Primarily a vegetarian, the grouse possesses a muscular gizzard capable of grinding buds 



• By Darid E. Dnil. 

 A S(?c Ar>pen(lii, p. 721. 

 t See dinnifliiion of Clamiiriration, p. 16. 

 t See dtncinininn of Voice, p. 98, 



