302 CALIFORNIA ACADEMY OF SCIENCES. 



sooty plumbeous. Feet black, bill pale. This bird is 

 not an albino, as is shown by the black wing tips, which 

 have much the same color arrangement as is exhibited 

 in the gulls." As Mr. Nelson also found other speci- 

 mens which were abnormally white, though not albinos, 

 it appears that these must be individuals which have 

 advanced beyond the species. The utility of a white 

 plumage to an Arctic bird like the snow bunting would 

 at first sight appear to be very manifest, yet, on further 

 consideration, it is found that the nest is not built in 

 the immediate vicinity of snow, and that accordingly a 

 white plumage would not be protective during the breed- 

 ing season. That the black is the earlier plumage and 

 the white a later phase, is proved by the fact that 

 the base of the feather is nearly always black, the tip 

 alone being white. This might be suggestive of a direct 

 influence of arctic cold in whitening the plumage, re- 

 gardless of utility. This view is strengthened by the 

 fact that it is during the winter months that the back is 

 white, this white edge of the feather wearing away at 

 the approach of spring (see Plate I, fig. 9). The back 

 of McKay's snowflake (P. hyperboreus) does not become 

 black in the breeding season, the white feathers remain- 

 ing unworn (Plate I, fig. 10); and this is to be expected 

 from the fact that the bird is more exclusively a resident 

 of the Arctic regions. Another factor which may have 

 aided in the production of the white plumage is that 

 white feathers containing gas bubbles are much denser 

 and warmer. The wings and tail, which do not form 

 part of the bird's clothing, would thus not need to change 

 to white, but would rather be of use as recognition mark- 

 ings by retaining their black hue. 



