YELLOW WABBLER 521 



California Yeli,ow Warbler. Dendroica aestiva brewsteri Grinnell 



Field characters. — Half size of Junco. Yellow color predominating; no black or 

 white markings whatsoever. Male: Clear yellow beneath (narrowly streaked with 

 chestnut, but this not discernible at a distance) ; upper surface greenish yellow. (See 

 pi. 9c.) Female and young: Pale yellow beneath, unstreaked; upper surface dull green- 

 ish yellow. Movements quick and nervous; hops along small branches in zigzag course. 

 Voice: Song of male very high pitched, piercingly shrill, 4 or 5 sharply enunciated notes 

 followed by quick series of shorter ones; call note a sharp tsip. 



Occurrence. — Common summer visitant at both bases and on adjacent lower slopes 

 of Sierra Nevada, extending up through the Transition Zone. Kecorded from Snelling 

 and near Lagrange eastward to Yosemite Valley; and again about Mono Lake. Chiefly 

 in cottonwoods and willows along streams, foraging up to 40 feet from the ground; 

 nests in same general surroundings, but usually less than 15 feet from ground. Solitary. 



Long ago the appellation "summer yellow bird" was given to the 

 Yellow Warbler in recognition of its clear yellow coloration and of the fact 

 that it comes to our latitudes only during the warmer months of the year. 

 The species is well represented in the Yosemite section from late spring 

 until early fall, and is found from Snelling and Lagrange eastward to 

 Yosemite Valley, and again, east of the mountains, near Mono Lake. 

 Everywhere it exhibits a strong preference for deciduous trees near streams. 



The California Yellow Warblers which are to nest on the west slope 

 of the Sierra Nevada arrive there some time before those individuals 

 destined to nest east of the mountains reach their particular haunts. Thus 

 yellow warblers were already present in Yosemite Valley on April 28, 

 1916, while in the same year the species was not noted near Mono Lake 

 until May 19. The fall departure takes place toward the end of August. 

 The birds do not wander to the higher zones, as do the Lutescent Warblers, 

 for example, but leave their nesting haunts rather early for the lowlands 

 to the west, en route to their winter quarters to the south of the United 

 States. Our own latest definite record for Yosemite Valley was made on 

 August 19 (1915), but Mr. Joseph Mailliard (1918, p. 19) states that in 

 1917 the species was present until somewhat later, disappearing in early 

 September. In 1920 the last seen by Mr. C. W. Michael (MS) in the 

 Valley was noted on September 11. 



Numerically the Yellow Warbler is an abundant bird within its 

 restricted environment. Fully 20 were seen or heard during a 4-hour 

 census taken in Yosemite Valley on May 31, 1915. These were practically 

 all in the cottonwoods, alders, willows, and in other deciduous growths 

 near the Merced River or its tributary streams. Similarly, along the lower 

 reaches of the big rivers where these emerge from the foothills, these birds 

 are plentiful in the month of May. 



