CASSIN VIREO 511 



Cassin Vireo. Lanivireo solitariiis cassini (Xantus) 



Field characters. — Three-fourths bulk of Junco; tail shorter than body. Plumage 

 grayish green above, olive gray on head; under surface whitish; eye encircled by white 

 (pi. 50a); two light bars on wing; bill black. Movements deliberate. Voice: Song of 

 male a series of detached notes, now rising, now falling in inflection, quee'-up, tseer, 

 etc.; call note a harsh che. 



Occurrence. — Common summer visitant to Transition Zone (sparing in lower Cana- 

 dian) on west slope of Sierra Nevada; recorded in nesting season from 3 miles east 

 of Coulterville and from El Portal, eastward to east fork of Indian Canon at 7300 feet 

 and to near Merced Lake at 7500 feet altitude. In spring migration passes through 

 lowland and foothill country, as at Snelling, Lagrange, and Pleasant Valley. In fall 

 small numbers wander to higher levels, as along McClure Fork to 8300 feet and along 

 course of Eafferty Creek. Not observed on east slope. Frequents chiefly incense cedars 

 and golden oaks. Solitary except when pairs are earing for broods. 



The Cassin Vireo is a summer visitant at middle altitudes along the 

 west flank of the Sierra Nevada, Its distribution at nesting time closely 

 parallels the ranges of the golden oak and incense cedar, though the bird 

 does not restrict itself exclusively to these two trees. In and around 

 Yosemite Valley this species and the Western Warbling Vireo are often 

 to be found together, although the Cassin shows preference for the drier 

 portions of the Valley, for example, near and upon the talus slopes along 

 the north and south walls. During the spring migration the Cassin Vireo 

 is a common transient in the western foothill country where, during its 

 passage, it is to be seen in blue oaks and chaparral on the dry hillsides. 

 In early fall after the young are grown a few of these vireos wander up 

 into the Hudsonian Zone before taking final leave of the country for the 

 winter. 



The first of the Cassin Vireos probably arrive in the Yosemite region 

 early in April. On our visit to El Portal on April 27, 1916, the species 

 was already well established there, and the same was found to be true 

 in Yosemite Valley the day following. Near Lagrange, in 1919, Cassin 

 Vireos were passing through the blue oak belt in numbers on May 7, and 

 a few transients were observed near Coulterville on May 9 and 10, while 

 in 1915, migration was still in progress at Bullion Mountain on May 26, 

 at Pleasant Valley on May 23 to 28, and at Snelling on May 27. In 1919, 

 however, nesting was already under way in Yosemite Valley on May 22. 

 It seems likely that the late migrants seen in the foothills in 1915 were 

 bound to some much more northerly station rather than that they were 

 going to swell the number in the Transition Zone of the region immediately 

 to the east. The species continued in evidence through August; single 

 birds were seen as late as September 1 near Echo Creek, September 2 

 in Yosemite Valley, and September 7 along Rafferty Creek, all in the 



