90 THE SPECIES-ITS TAXONOMY, RANGE. BIOLOGY, & ECONOMIC IMPORTANCE 



Fourteen to Seventeen Weeks 



The growth of the aduU flight feathers during this ])eriod is completed at the following 

 intervals: number 11 secondary — 14 to 15 weeks; number 12 secondary — 16 weeks; num- 

 ber 3 primary — 17 weeks. The number 13 secondary has also completed its growth by the 

 seventeenth week and this is followed within one or two days by completion of the numbers 14 

 and 15 secondaries. 



2 3 4 5 6 7 

 PRIMARIES 



9 \0 -i Z 3 4 5 6 7 B 9 10 I I 12 13 14 15 

 2 SECONDARIES 



^^H Feother noi t^et visible 

 Juvenal feQ4 he rg rowing I i Adult Teafber growing 



Juvenal feofher fully 

 developed 



M Adult feather fully 

 developed 



FIGURE ^). KKLATIVK DEVELOPMENT AT WEEKLY INTKKVAI.S OF \VIN(. FEATHERS OF VOUiNC 



GROUSE 



Beyond tiiis jjoint no important changes in llii- ailult piunuiiic lake place until tin- follow- 

 ing spring. As has been described, however, birds of the year may be distinguished from 

 older individuals by the presence of the bursa Fabricii and the character of the first two 

 |)rimaries. 



WEIGHT* 



Grouse weights are interesting as a species diarartcristic and inipmlanl as one of the 

 major yardsticks by which the health of the individual birds may be judged. Factors af- 

 fecting weight run the gamut from onviroiunental influences, such as shelter, food and weath- 

 er, to those of a pathological or physiological nature. Activities requiring the expenditure of 

 unusual amounts of energy, notably courtship and egg laying, as well as physiological changes 

 associated with age differences and moulting, are imjiorlant rauses of weight loss. Also, re- 



* By Gardinrr Bump. 



