136 CALIFORNIA ACADEMY OF SCIENCES. 



sometimes broader and the ashy edging so narrow that 

 the tip wears down to the black. Figure 7 is a feather 

 from the back of the head of the western warbler 

 {Dendroica occidentalis) , in winter plumage. In this in- 

 stance the brown edging wears off leaving a yellow 

 feather with a black dot at the tip. In full plumaged 

 birds all this black wears away leaving the head uni- 

 form yellow. Figure 8 is a feather from the breast of 

 the rusty blackbird (Scolecophagus carolinus), in winter 

 plumage. In the above two instances the brown was so 

 complete as to produce a uniform color, but with the 

 rusty blackbird it is less regular, causing a mottled effect. 

 The brown tip wears off in spring leaving the plumage 

 clear black. Perhaps the two most interesting examples 

 of all, however, are represented in figures 9 and 10 of 

 feathers from the backs of the two species of snow-bunt- 

 ings {Plectrophenax nivalis and P. hyperboreus) , nearly 

 in breeding plumage. In P. nivalis (fig. 9), the broad 

 white terminal portion has almost entirely worn away 

 leaving the black base exposed, but it does not wear off 

 thus in P. hyperboreus, the black remaining white 

 through the breeding season. 



Mr. Yarrell says: " Young birds of the year in vari- 

 ous species, after the autumn moult, continue through 

 the winter to assume, by degrees, the more intense 

 colours characteristic of adults, without changing the 

 feather. This colour commences generally at that part 

 of the web nearest the body of the bird, and gradually 

 extends outwards till it pervades the whole feather." 

 He calls attention to the influence of the sexual organs 

 in changing plumage. Many birds appear to become 

 more brilliant in color as the breeding season ap- 

 proaches without either a moult or the wearing away of 

 the tips of the feathers (acraptosis) . This I believe is 

 tlie case with the house finch (Garpodacus mexicanus 

 frontalis). 



