THE AMERICAN MUSEUM JOURNAL 



CLIMATIC Vx^RIATION IN COLOR AND SIZE OF SONG 



SPARROWS. 



Illustrating Evolution by Environment. 



I HE first exhibit of several designed to illustrate 

 variation in the color and size of birds due to 

 climatic agencies, has recently been placed in the 

 local bird hall and is here figured. It includes 

 the leading types of Song Sparrows, a species 

 which is particularly susceptible to the influences of its environ- 

 ment, no less than twenty climatic varieties, geographical races, 

 or subspecies of this wide-ranging bird being known. 



Observe that east of the Rocky Mountains, in a region where 

 climatic conditions are quite uniform, only one well-marked sub- 

 species of Song Sparrow is found ; but that 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. 



Note the striking relation between the colors of the various 

 races and the aridity and the humidity of the areas they inhabit. 

 Thus the palest-colored race, the Desert Song Sparrow (No. 5, 

 Melospiza cinerea fallax) , 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-colored race, the Sooty Song Sparrow (No. 2, 

 Melospiza cinerea riifina), inhabits the most humid portion of 

 North America, the coast region of British Columbia and south- 

 ern 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 Spar- 

 row (No. I, Melospiza cinerea cinerea), is the most northern, and, 

 the smallest race, the Mexican Song Sparrow (No. 6, Melospiza 

 cinerea mexicana), is the most southern. 



Between the lightest and darkest, the smallest and largest. 

 Song Sparrows, however, there is comj)letc intergradation in 

 accordance with the change in the conditions which afi^ect their 



color and size. f. m. c. 



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