1920] Swarth: Revision of Avian Genus Passerella 95 



in the winter home of the northern forms. Fuliginosa (the darkest 

 colored subspecies) migrates the least of any, probably occurring 

 throughout the j^ear in the same general region as that in which it 

 nests. Its habitat is in part a region where there is a tremendous 

 annual rainfall, but 80 per cent of this precipitation occurs during 

 the winter months. The summers are to a great extent hot, dry, and 

 sunny, with but occasional rainstorms. 



Taking the whole year through, it is evident that the darkest 

 colored forms (annectens, townsendi and fuliginosa) are under more 

 or less humid conditions continuously, and during the winter months 

 under an extreme of such exposure. Of the paler colored races 

 {unalaschcensis, insularis and sinuosa), one at least {sinuosa) nests 

 in a region of extremely heavy precipitation, and the others where 

 fogs and cloudy weather prevail much of the time, but they all spend 

 the winter, a longer period than the nesting season, in an arid portion 

 of the country. 



Thus, to summarize, while the maximum of humidity in summer 

 lies in the stretch of country extending from Prince William Sound 

 through the Alexander Archipelago, the extreme of dark brown 

 coloration in Passerella occurs, not in this region, but to the south- 

 ward, about Puget Sound. The curious feature of the whole case is 

 that if humidity throughout the year were really the controlling factor 

 in the coloration of these birds, the balanced effects of summer and 

 winter surroundings should have produced such a nicely graded series 

 of steps in the color changes from one extreme to the other, from 

 unalaschcensis to fuliginosa. There would seem to be an opening 

 here for arguments favoring a pre-determined line of evolution — as 

 regards direction through space, however, rather than through time, 

 the manner in which such a theory is generally applied. 



In connection with the above argument attention may be directed 

 to the song sparrow {Melospiza melodia), as it occurs on the north 

 Pacific coast. Different subspecies correspond closely in habitat with 

 the several subspecies of Passerella, and exhibit the same general 

 trend of color variation as is seen in the latter. In Melospiza, however, 

 while the extreme of dark reddish brown coloration does occur in the 

 Puget Sound region (the habitat of fuliginosa), this coloration is 

 practically the same as in the bird of the Sitkan district. The north- 

 west coast song sparrows are so much less migratory than the fox 

 sparrows that it is hard to draw comparisons regarding the relative 

 effect of summer conditions as opposed to conditions throughout the 



