IIO Grinnell, Geographical Abrasion in Birds. I ^" 



but with flanks and upper parts paler and less rufescent. It is 

 further explained to be "usually paler than ustulata., and has very 

 much less of rufous tinge to the upper surface, including both 

 wings and tail ; the sides and flanks are more grayish ; the buff of 

 jugulum somewhat paler. Although most of these chai'acters are 

 not entirely constant, typical specimens may be without difficulty 

 discriminated " (!). There is admittedly " no material difference 

 in size " ; so here we have to do with color differences only. 



In carefully examining my series, as above enumerated, I find 

 that the darkest Sitkan example (No, 1188, June 26) is slightly 

 more rufescent than any from California, while another example 

 from Sitka (No. 11 19, June 11) is paler and more olivaceous than 

 any California specimen taken before June i. The rest of the 

 Sitkan skins (June and July) are all easily matched by as many of 

 the breeding birds taken at Palo Alto in May. The most oliva- 

 ceous skins I have are Nos. 4748 (June 22) and 4794 (July 10), 

 taken at Pacific Grove, and No. 4277 (June i), taken at Palo Alto. 

 These are much paler than any from Sitka (except No. 11 19), and 

 are correspondingly far more worn. If the Sitkan series is repre- 

 sentative of the " Northwest Coast region," I fail to see that they 

 are any darker than California breeding birds at the same stage of 

 abrasion. The greater rate of fading to which California birds 

 seem to be subject, must also come into play, causing a generally 

 paler effect in a large series of summer birds from California. At 

 any rate, judging from my own material I see no evidence of a race 

 ' osdica.'' 



Hylocichla ustulata ustulata of the Pacific Coast, H. u. almce from 

 the Great Basin and Rockies northward, and H. u. s7t'a//isou/ oi the 

 Eastern province, each possesses distinguishing color characters. 

 Each occupies a separate region in summer, and each seems to 

 follow a separate north-and-south migration route. The conditions 

 governing H. ustulata^ and H. aonalaschkce (of many recognizable 

 races) seem to consist in a different extent of migration. The 

 former has a long migration route, sweeping south into Mexico 

 early in the fall, and back again late in the spring. The 

 H. aonalaschkce group have a much shorter migration route, some 

 of the races not going south of the United States ; and in winter 

 occupying areas nearly as circumscribed as in summer. The less 



