°Sai I Ridgway, Geographical Variation in Sialia mexicana. I JO 



The amount of chestnut on the back is usually more or less 

 correlated with a similar variation of that on the breast ; but not 

 always so. Of the specimens now at hand of S. m. occide?italis 

 in its larger sense (that is, including both the typical form and 

 the chestnut-backed style which I have named, provisionally, 

 S. m. bairdi), only 6 out of a total of 65 have the chestnut of the 

 breast nearly or quite divided into two lateral patches, these all 

 of the western style, the localities represented being as follows: 

 Ft. Steilacoom, Washington, 1 (April 17) ; Mt. Lassen, Cali- 

 fornia, 1 (July 4); Nicasio, California, 1 (April n); Mt. 

 Whitney, California, 1 (October 23) ; Carson City, Nevada, 1 

 (February 21); and Genoa, Nevada, 1 (June 20). These all 

 have very little chestnut on the back, amounting in the Genoa 

 specimen to a mere trace, observable only on the closest 

 inspection. 1 



The chestnut on the breast is as a rule decidedly broader in 

 the birds with wholly brown backs, but occasionally an example 

 with very little chestnut on the back will be found with the 

 maximum width of that color across the breast. There is so 

 much individual variation in the intensity of this color that it is 

 difficult to tell whether in one form it averages deeper than in 

 the other ; but apparently it averages paler in the coast form. 



From the foregoing it will be seen that while the presence or 

 absence of chestnut on the back and the degree to which it is 

 developed is largely a variable individual character and only 



Dr. A. K. Fisher has examined a series of 10 adult males in the collection of the 

 Division of Ornithology, U. S. Department of Agriculture, with the view of testing 

 this character, and kindly submits the following result : — 



Back with more or less blue : Pyramid Lake, Nevada, 2 (June 24) ; Prescott, Ari- 

 zona, 1 (June 21). 



Back entirely chestnut : Fort Davis, Texas, 1 (Jan. 2) ; Kanab, Utah, 1 (Dec. 26); 

 San Francisco Mts., Arizona, 1 (August) ; Charleston Mts., Nevada, 1 (February) ; 

 Mt. Whitney, California, 1 (Sept. 4) ; San Bernardino, California, 2 (Dec. 30). 



It will thus be seen that this material, in the main, bears out the geographical signi- 

 ficance of the variation in question, though the two examples with wholly chestnut 

 backs from Beaverton, Oregon (which is on the west side of the mountains and 

 near the Columbia River), in addition to other exceptions to the rule, show clearly 

 that the variation is not strictly geographical. 



1 These six examples bear a very close resemblance to S. in. anabelce, but may be 

 separated by their decidedly more slender bill, and, except in the case of the one from 

 Fort Steilacoom and that from Genoa by the perceptibly lighter shade of blue and 

 lisrhter chestnut on the sides of the breast. 



