312 BULLETIN 197, UNITED STATES NATIONAL MUSEUM 



VIREa SOLITARIUS CASSINl Xantus 

 CASSIN'S VIREO 

 HABITS 



Cassin's vireo is the westernmost race of the species, breeding from 

 the Rocky Mountains westward and mainly in the Transition Zone, 

 from central British Columbia to northern Lower California. It 

 differs from the eastern blue-headed vireo in being slightly smaller 

 and much duller in color. 



In the northern portion of its range, Cassin's vireo seems to prefer 

 the forests of pines and firs, where there is a mixture of oaks or other 

 deciduous trees among the conifers. S. F. Rathbun tells me that it is 

 a regular and not uncommon summer resident about Seattle, Wash., 

 where it prefers the rather open sections of the forest where there is 

 a somewhat scattered growth of trees ; he also finds it where there is 

 a mixture of deciduous trees among small firs, but considers it rather 

 partial to oaks. 



Gabrielson and Jewett (1940) say that, in Oregon, "it is found in 

 the smaller second growth and in brushy areas either on the hillsides 

 or along the stream bottoms. * * * It breeds commonly and 

 builds its dainty nest low in bushes or trees." Dr. J. C. Merrill (1888) 

 writes: "Unlike most Vireos this one, as observed at Fort Klamath, 

 shows a marked predilection for pines and firs, and is found almost 

 everywhere among these trees. It is also found, but much less fre- 

 quently, in aspen groves with the Warbling Vireo. The nests are 

 built in low manzanita or buck-rush bushes that grow throughout the 

 pine woods." Grinnell and Storer (1924) write: 



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 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. 



Howard L. Cogswell writes to me : "In the San Gabriel Mountains, 

 the area where I have seen most of my Cassin's vireos, they are defi- 

 nitely associated in the breeding season with the oaks along the walls 

 of the lower mountain canyons and throughout the big-cone spruces 

 and golden-cup oaks and into the lower edges of the pines of the 

 Transition Zone. They are not often found in the alders and syca- 



