374 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lu 



individually with little attention to the overall pictiu'e of variation 

 throughout the range. The present study is an attempt to evaluate 

 the significance of color differences with particular emphasis on their 

 value as racial characters. 



Historical Summary 



In early accounts of North American birds there is much confusion 

 concerning the nomenclatm-e of the five common smaller thrushes. 

 jMost of the names used for the present species had either a composite 

 base or were preoccupied. Wilson (1812, pi, 43, fig. 2) illustrated 

 the species but referred to it as a "hermit thrush," and in the accom- 

 panying text (p. 95) listed it as Turdus solitarius, a name antedated 

 by Turdus solitarius Linnaeus of 1758 for another species. Nuttall 

 (1840, pp. 400, 830) proposed Turdus ustulatus for the russet-backed 

 population from Oregon, the first valid name for the species as a whole. 



Swainson (Swainson and Richardson, 1832, p. 183) had earlier 

 given an excellent description of an olive-backed thrush killed at 

 Carlton House, Saskatchewan, in May 1827, but beheving this bird 

 to be the "tawny thrush" of Wilson, listed it as "Merula Wilsonii 

 Bonaparte" from T[urdus] Wilsonii Bonaparte (1824, p. 34). 



Cabanis (in von Tschudi, 1845, p. 28) perceived that Swainson 

 had misidentified the bird from Carlton House and proposed the new 

 name (in Mss.) T[urdus] Swainsoni. This is accepted as the sub- 

 specific name for the eastern population, and is the second valid name 

 available. 



Baird (1864, pp. 18-19) treated the eastern and western groups 

 of Swainson 's thrush as separate species under the two names Turdus 

 swainsonii and Turdus ustulatus respectively. 



In the same pubhcation (p. 12) he erected the subgenus Hylocichla 

 for the small North American thrushes. 



Coues (1872, pp. 72-73) listed the "ohve-backed thi-ush" in Baird's 

 subgenus Hylocichla under the name swainsoni and included the gray- 

 cheeked thrush (Hylocichla minima) as the variety "aliciae, Alice's 

 thrush," in addition to ustulatus. 



In fm-ther studies, Baird and Ridgway (Baird, Brewer, and Ridg- 

 way, 1874, p. 7) separated the gray-cheeked thrush as a distinct 

 species and recognized swainsoni and ustulatus as varieties of a single 

 species for which, however, they continued to use the younger name 

 T. swainsoni. 



The presently accepted trinomials Hylocichla ustulata swainsoni 

 (Tschudi) and H. u. ustulata (Nuttall) came into official use with the 

 pubhcation of the third edition of the A.O.U. Check-List (1910). 



Oberholser (1898, p. 304) gave his attention to the population from 

 the southern Rocky Mountain area and concluded that they were 



