The Least Vi re os 
No. 118 
Least Vireo 
No. 118a California Least Vireo 
A. O. U. No. 633a, part. Vireo belli pusillus Coues. 
Description. — Adult: Upperparts plain mouse-gray, shading on sides of head, 
neck, and breast, the pileum faintly varied by brownish gray; back, scapulars, and rump, 
faintly, sometimes very faintly, glossed with olivaceous; underparts white, the breast 
sometimes lightly tinged with palest grayish olive; sides lightly washed, or not, with 
pale greenish yellow; axillars pale sulphur-yellow; a pale whitish supraloral area; 
lores, narrowly, dusky; eyelids, narrowly, especially below, black, then white; the 
major feathers of wings and tail with paler edgings; the greater coverts definitely tipped 
with pale grayish white. Bill horn-colored above, pale or flesh-colored below; feet and 
legs bluish dusky; iris brown. Length about 120.6 (4.75); wing 55.3 (2.18); tail 51 
(2.01); bill 9.5 (.37); tarsus 19 (.75). 
Recognition Marks.' —Pygmy size; plain gray above, white below; slight tinge 
of olivaceous, especially on sides; song of “breathless jumbled notes.” 
Nesting. — Nest: A semi-pensile basket lashed by edges to fork of horizontal 
or descending branch of tree, at lower levels—2 to 5 feet above ground; composed of 
bark-strips, dry leaves, and grasses; lined with fine grasses or, rarely, felted with 
plant-down. Eggs: 3 or 4, rarely 5; white, speckled and spotted sparingly, and chiefly 
at larger end, with reddish brown or brownish black. Av. size, as in next form. Season: 
May-June; one brood. Extreme dates given by Willett, on authority of H. Robert¬ 
son, Los Angeles, Apr. 1, 1900, 3 newly hatched young; Los Angeles, June 30, 1898, 3 
eggs. 
Range of Vireo belli.- —Western United States east to the Mississippi Valley, and 
Mexico. 
Range of V. b. pusillus. —Central and southern California and northern Lower 
California, and east possibly to southwestern Nevada; breeding south to San Pedro 
Martir Mountains and San Fernando, Lower California; south in winter to Cape San 
Lucas and probably the west coast of Mexico. 
Distribution in California. —Summer resident in riparian associations of the 
Lower Sonoran zone, breeding north in the central valley to Marysville (Belding), and 
in the coastal counties, north at least to southern Monterey County (San Ardo, May 
14, 1916, eggs taken); recorded east of the Sierras north to Bishop Creek (A. K. Fisher). 
Status of bird’s breeding in desert counties east of the main divide undetermined— 
may be V. b. arizonce. 
Authorities.—Coues ( Vireo pusillus ), Proc. Acad. Nat. Sci. Phila., 1866, p. 76, 
part (orig. desc.; type locality Cape San Lucas, Lower Calif.; also ascribed to “Southern 
California”); McAfee, U. S. Dept. Agric., Yearbook, 1906, p. 194 (feeding on scale 
insects); Grinnett, Condor, vol. xiv., 1912, p. 106 (song); Tyler, Pac. Coast Avifauna, 
no. 9, 1913, p. 98 (Fresno; habits, song, nest and eggs, etc.); W. C. Hanna, Condor, 
vol. xx., 1918, p. 211 (San Bernardino Valley; descr. of nests occupied by Cowbirds). 
No. 118b Arizona Least Vireo 
A. O. U. No. 633a (part). Vireo belli arizonae Ridgway. 
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