600 ANIMAL LIFE IN THE YO SEMITE 



Russet-backed Thrush. Hylocichla ustulata ustulata (Nuttall) 



Field characters. — Size nearly twice that of Junco; bill i^hort and slender. Whole 

 upper surface plain brown; wing with a concealed band of buffy which shows in flight; 

 breast buffy with scattered triangular spots of brown; sides brownish, not streaked; 

 belly white; eye surrounded by a narrow ring of buff. (See pi. lib.) Movements 

 deliberate. Voice: Song of male a set theme, 2 to 4 deep clear notes, then an equal 

 number of slurred ones, ascending in pitch, the last one finely attenuated ; call note a 

 soft Avhistled what or trhoit ; less often a harsher chee-ur-r. 



Occurrence.- — Summer visitant in Transition Zone on west slope of Sierra Nevada. 

 Eecorded as nesting in Yosemite Valley and in vicinity of Bower Cave, and as a transient 

 at Snelling and Pleasant Valley, and near Coulterville. Keeps to low growths near 

 streams, males going up into trees to sing. Solitary. 



The Russet-backed Thrush is extremely local in its occurrence in the 

 Yosemite region. In fact we found it at nesting time only on the floor 

 of Yosemite Valley and in the vicinity of Bower Cave. In the Valley it 

 is usually present in some numbers and during the early part of the sea.son 

 may be heard in song about many of the camps. 



This species resembles the Hermit Thrush in general appearance though 

 it can be told easily from that bird. (See pi. 11.) The Russet-back is 

 uniformly colored above, having no rufous tinge on the upper surface of 

 the tail ; it does not twitch its \^'ings or raise and lower its tail in the manner 

 of the Hermit Thrush. In point of size the present species is the larger, 

 in the ratio of about 32 to 25, the average weight in grams for the two ; 

 but this difference in bulk is not enough for separating the two thrushes 

 out of hand. The songs and calls are totally different and whenever heard 

 are the most certain means of identifying their possessors. 



In the month of May Russet-backed Thrushes are likely to be encoun- 

 tered as transients at almost any station in the foothill country. We noted 

 the species at Snelling on May 26 to 29, 1915, and at Pleasant Valley on 

 May 24 and 25 the same year. In 1919 it was observed near Coulterville 

 on May 10 and 11. All the birds seen by us at these places acted as though 

 they were merely resting and foraging while en route to more northern 

 localities. Through much of May and on until some time in July Russet - 

 backed Thrushes are much in evidence in Yosemite Valley, but they begin 

 to disappear toward the end of the latter month and are seen but seldom 

 thereafter. It is not known whether the bulk of the population migrates 

 early or not; more likely their added reclusiveness at the season of molt 

 tends to remove them from human view. Mr. C. W. Michael (IMS) who 

 kept continuous record of the birds in Yosemite Valley during the sea.son 

 of 1920 observed the Russet-backed Thrush almost daily until July 24. 

 Thereafter it was noted upon but three occasions, namely, August 27, and 

 September 1 and 11. And each of these records was for onlv a single bird. 



