266 BULLETIN 19 7, UNITED STATES NATIONAL MUSEUM 



rump and uper tail-coverts (and there obviously only in fresh plu- 

 mage) ; under parts nearly pure white, including under tail-coverts, 

 the sides and flanks washed with pale olive-gray or grayish olive, 

 but with only the merest trace of yellow tinge ; wing and tail averaging 

 longer. Young with upper parts decidedly paler and grayer, and 

 under parts of body, with under tail-coverts, pure white throughout." 



The haunts of the least vireo in California are similar in a general 

 way to those of Bell's vireo in the Central States, mainly dense thickets 

 of willows and low bushes along streams or damp places, or in alder 

 thickets in wet bottom lands. In the Lassen Peak region, according 

 to Grinnell, Dixon, and Linsdale (1930), "it lived for the most part 

 near the ground in the stream-side willow thickets. Individual birds 

 were seen also to forage into grapevine tangles, valley oaks, and live 

 oaks. * * * The closest avian associate of the least vireo was the 

 yellow warbler. For example, a mid-river island in the Sacramento 

 two miles or so above Red Bluff, and comprising about ten acres, har- 

 bored on May 7 three singing male vireos and eight singing male 

 warblers. But in foraging, the vireos kept near the ground, below 

 about the 3-foot level, while the warblers kept mostly above that 

 level." 



Nesting. — Grinnell and Storer (1924) record a completed nest that 

 they found in the Yosemite region on May 8, 1919 : 



It was in deep shade under a tbicket of willows and white alders which gi'ew 

 on the lower slope of a pile of gravel left by a gold dredger. The nest was 19 

 inches above the gravel, and instead of being placed in one of the stout crotches 

 of the adjacent alder it liad been lashed to a slender fork on the brittle stem of a 

 vpeed of the previous season's growth. This was only 7 feet from the margin of 

 a pool of quiet water. In form the nest was a well rounded, deep and rather 

 thin-walled cup with slightly inrolled rim. It was composed of dry shreds of 

 plants felted compactly with down from cottonwoods and willows. Outside, it 

 measured 2 inches in height and 2iA inches in greatest diameter, while the interior 

 was 114 incites deep at the center and about 1% inches across the opening. 



In what was once called Nigger Slough, near Los Angeles, on May 

 30, 1914, we found a least vireo's nest containing two eggs ; it was hung 

 in a fork of a slender willow sapling in a thicket of these trees, 7 feet 

 above the damp ground ; in construction, it was similar to the one men- 

 tioned above. 



The nests often contain cowbirds' eggs, as do all other races of this 

 common host. 



Eggs. — The eggs are like those of the species elsewhere. The meas- 

 urements of 40 eggs in the United States National Museum average 

 17.4 by 12.7 millimeters; the eggs showing the four extremes measure 

 19.1 by 12.2, 18.0 by 13.2, and 15.8 by 11.2 millimeters. 



Behavior. — Grinnell, Dixon, and Linsdale (1930) watched a pair 

 of these vireos on April 23, 1928, in what may or may not have been 



