■18 



METHODS A \I) TECIINIQVES 



to be the iiiosl easily identified colors. White leghorn chickt-ii feathers were used. Coh>rs were 

 obtained by using the following commercial dyes: 



Yellow — Wool Yellow — Extra Concentrated 

 Orange — Wool Orange — 2 G Crystals 

 Pink — Croceine Scarlet M 0. 

 The marking feathers were easily visible and usually remained until the tail feathers were 

 moulted during late August. 



All birds were weighed and aluminum leg bands put on before release. Blood smears were 

 taken, in a number of cases, from a vein in the wing. 



Determining Sex and Ace 



Insofar as laboratory techniques were possible, sex was determined by dissection and exam- 

 ination of the internal organs*. External appearance and behavior have also been used as 

 discussed elsewhere'^. 



No means of determining age beyond one year is known. In order to distinguish birds 

 of the year from adults of more than one year the presence or absence of the bursa Fabricii 

 afforded the best criterion. This is a sacular structure which opens into the cloaca. It is pres- 



REAR PORTION OF BODY CAVITY OF A BIRD OF THE YEAR (LEFT) SHOWING BURSA AS COMPARED 



WITH THAT OF AN OLDER BIRD 



ent in young birds but is absent in adults. Its use as an index of age in game birds was 

 pointed out by Gower"^. Experience has indicated that in grouse the bursa may be relied 

 upon to separate birds of the year from adults through February and that a certain number 

 of birds may show bursae during March and April, though its absence during these months 

 does not necessarily mean that a specimen is not a bird of the year. Another feature which 

 has also been used is the character of the first two primaries, since the juvenile feathers 

 are not moulted until the late winter of a bird's first year'f. 



USE OF RIOMETRICAL ANALYSIS 



Throughout this book references have been made to the use of biometrical methods in the 

 analysis of data. When the Investigation was organized in 1930 advanced statistical techniques 



* Sec Anatoui), p. "40. 

 A Sec Chapter U, p. 39. 

 t See Chaplcr \\, p. 84. 



