BIRDS OP NORTH AND MIDDLE AMERICA. 



56 



Turdus swainsoni (not of Cabanis) Lawrence, Bull. U. S. Nat. Mus., no. 4, 1876, 



11 (Tehuantepec). 

 [Turdus] sivainsoni Sclater and Salvin, Nom. Av. Neotr., 1873, 1, part. 

 Hylocichla ustulata oedica Oberholser, Auk, xvi, Jan., 1899, 23 (Santa Barbara, 



California; coll. U. S. Nat. Mus.).— Belding, Bull. Cooper Orn. Club, i, 1899, 



29 (note on song). — ^American Ornithologists' Union Committee, Auk, 



xvi, 1899,127 (checklist no. 7586). 

 Hlylocichla] u{stulata] oedica Bailey (Florence M.), Handb. Birds W. U. S., 1902, 



470.— Coues, Key N. Am. Birds, 5th ed., i, 1903, 255. 



HYLOCICHLA USTULATA SWAINSONII (Cabanis). 

 OLIVE-BACKED THRUSH. 



Similar to H. u. ustulata, but color much grayer or more olivaceous; 

 color of upper parts varying from olive to grayish hair brown in sum- 

 mer, from deep olive to slightly brownish olive in winter; spots on 

 chest averaging broader and darker (sometimes sooty blackish) on a 

 more yellowish buff or creamy buff ground color; sides and flanks 

 olive or grayish olive. 



Adult ma/^.— Length (skins), 158-176 (166); wing, 96.5-105 

 (100.9); tail, 66-77.5 (70.1); exposed culmen, 11.5-14.5 (13); tarsus, 

 26-31 (28); middle toe, 15-18 (16.6).« 



Adult female.— ^Length (skins), 147-173 (161); wing, 92.5-102.5 

 (97); tail, 61.5-74 (66.1); exposed culmen, 11.5-14 (13.8); tarsus, 

 25.5-29 (27.1); middle toe, 15.5-18 (16.4).'' 



o Thirty-five specimens. 

 b Thirty-two specimens. 

 Specimens from different geographic areas average, respectively, as follows: 



I am not able to discover any constant difference between eastern specimens, on the 

 one hand, and western and Alaskan specimens, on the other. In fact, when specimens 

 of corresponding date are compared the average difference, if any exists at all (there is 

 certainly none in autumnal examples and little, if any, in those taken in spring), is 

 too slight, in my judgment, to warrant the recognition of two geographic forms or sub- 

 species. A considerable series of specimens taken in Alaska in July look grayer than 

 a smaller number taken in the mountains of Pennsylvania in June; but even allowing 

 for the greater abrasion and fading of the former, occasional specimens from the two 

 regions are practically identical. 



