1914] Grinnell: Mammals and Birds of the Colorado Valley 197 



from six to nine per cent on either side of the mid-point; that the 

 wing' length is most constant; that in average dimensions females are 

 smaller than males except that the bills in the former are slightly the 

 larger. 



Although little more than three weeks apart in time of capture, 

 the May birds are distinctly more worn than those of April 18. This 

 undoubtedly accounts for the slight lessening in wing length, and 

 also modification in wing formula, as exhibited bottomwards in the 

 appropriate columns. In obtaining the wing formula as given, the 

 primaries are numbered consecutively from the carpal joint distally. 

 The numbers are arranged in order of relative length of the primaries, 

 the first given being the longest; thus 8-7-6-9-5-4-3-2-1 means that the 

 eighth primary is longest, the seventh next in length, and so on. 

 Since in this bird the primaries proximally from number 5 in all 

 individuals decrease in length with regularity, only the variable 

 (outer) portion of the formula is given. The variation in wing for- 

 mula as shown in the table appears to be greater than it really is, for 

 in most cases 6, 7, and 8 are very nearly of a length, 9 being propor- 

 tionally shorter but in no case as short as 5. Eight and 7 are most 

 frequently of greatest length. 



In coloration the females are paler, being more ashy and less yellow 

 than in either D. aestiva aestiva or D. aestiva brewsteri. The males, on 

 the other hand, have the yellow more intense and extensive, involving 

 the whole head and back, and represented on the wings and tail by 

 much broader edgings. The green mantle of brewsteri is represented 

 in sonorana by a more restricted area of dull yellow, the whole head 

 and rump being brightly yellow. The yellow of the crown is often 

 tinged strongly with chestnut, and the dorsum is streaked narrowly 

 with a darker tone of the same color. The underparts are even more 

 narrowly chestnut-streaked than in brewsteri. Variation in the latter 

 respect is considerable, from a case where the ventral streaking is 

 scarcely perceptible to the opposite extreme, where the streaking is 

 about as well defined as in average brewsteri. 



Sonorana, as shown by the present series, is an easily recognized 

 form, in spite of its great range in individual variation. For, among 

 so many characters, where one fails, others are left to hold to. 



