184 CALIFORNIA ACADEMY OF SCIENCES. 



According to this same principle of the conspicuous- 

 ness of moving parts, other markings may possibly be 

 explained. A considerable number of birds have the 

 edge of the wing along the shoulder, decidedly marked 

 with yellow, white, rose, etc. It is especially on the 

 under side of the wing and not very readily seen when 

 the bird is at rest. During the courting season the males 

 of many species have a habit of rapidly vibrating their 

 wings in a slightly lowered position. I have noticed 

 this among the sparrows such as GambePs sparrow 

 (Zonotrichia leucophrys gambeli), and I think the western 

 savanna sparrow (Amrnodravius sandivichensis alaudi- 

 nus). It is probable that this habit obtains with the 

 grasshopper sparrow (A. savannarum passerinus) in 

 which the wing is so conspicuously edged with yellow, 

 and has been developed by selection in the same man- 

 ner as the throat patch. Frequently the under wing 

 coverts are colored peculiarly and sometimes very beau- 

 tifully, as in the rose-breasted grosbeak. When the 

 male bird is paying his addresses to the female this 

 patch would be sometimes obscured and sometimes visi- 

 ble, and accordingly more conspicuous and beautiful 

 than if always in plain sight. Audubon, in his plate of 

 this species, represents a male facing a female with 

 wings raised to show this patch, but it may be that he 

 drew it thus in order that the spectator might see the 

 marking, and not because he had ever seen the birds in 

 that attitude. The rump is very frequently colored dif- 

 ferently from the back and tail (as in Dendroica coronata), 

 or when colored the same is more intense (as in Carpo- 

 dacus mexicanus frontalis). When courting, the wings 

 and tail are lowered and the rump accordingly is very 

 conspicuous. The under tail coverts are frequently col- 

 ored differently from the belly or tail, and generally in 

 species which live amongst the underbrush dodging 



