Climatic Variation in Color and Size of Song Sparrows 165
but west of the Rocky Mountains. where there are widely varying climatic conditions. sixteen subspecies of Song Sparrow are known. twelve of them from California alone.
There is a striking relation hetween the colors of the various races and the aridity and the humidity of the areas they inhabit. Thus the pales!- colored race, the Desert Song Sparrow (No. 5. on the accompanying illus» tration). ll/Ielarpiza rim'rm [cl/ax inhabits the most arid portion of North America. the desert region of Nevada. Arizona and southeastern California. where the annual rainfall averages about six inches: while the darkest—col» ored race. the Sooty Song Sparrow (Not 2. Allrlos/tiza rimrm ru/inu), inhabits the most humid portion of North America. the coast region of British Columbia and southern Alaska. where the annual rainfall may reach one hundred and twenty-five inches.
Note that. in obedience to the law that animals increase in size toward the north. the largest race. the Aleutian Song Sparrow (No. I. Alrlnr/ziza tinzrm tinzrm ), is the most northern. and. the smallest race. the Mexican Song Sparrow ( No. 6. file/9min: (intrm mrxirmm l. is the most southern
Between the lightest and the darkest. the smallest and the largest Song Sparrows. however, there is complete intergradation in accordance with the change in the conditions which affect their color and size.
NIGHTHAWK an MST
Fvnm Natale. h) J. E. Scchold.Catlxsle. l’a.
