476 THRUSHES, SOLITAIRES, BLUEBIRDS, ETC. 
Nest. — In holes in trees, stumps, posts, or bird-boxes; made largely of 
dried grasses. Eggs: 4 to 7, plain pale greenish blue. 
Food. — Largely caterpillars, grasshoppers, and crickets; also wild ber¬ 
ries, like liackberry and woodbine. 
The eastern bluebird ranges west to the base of the Rocky Moun¬ 
tains, being a rare summer resident in Colorado. 
766a. S. S. azurea Baird. Azure Bluebird. 
Similar to sialis, but sides of neck brown, and under parts less ruddy 
brown; upper parts sometimes greenish blue, suggesting arctica. Length : 
0.40-7.10. Male: wing 4.05-4.20, tail 2.70-2.95, bill .47-.50. Female: 
wing 3.90, tail 2.55. 
Distribution. — Southern Arizona and Mexico. 
767. Sialia mexicana occidentalism Towns.). Western Blue¬ 
bird. 
Adult male. — Upper parts dark purplish blue and chestnut; throat pur¬ 
plish blue; breast dark rufous; rest of under parts mixed brown, dull 
purplish and gray. Adult female: head, neck, and upper parts gray, washed 
with brown on back; rump and tail bright blue; outside tail feathers 
edged with white. Young: like young of sialis, but bill slenderer. Male: 
length 6.50-7.12, wing 3.95-4.45, tail 2.62-3.05, bill .45-.50. Female: 
wing about 4, tail 2.50. 
Distribution. — Breeds in Transition zone of the Pacific coast, from Brit¬ 
ish Columbia to California, and east to western Nevada and Idaho; casu¬ 
ally during migrations to New Mexico. 
Nest. —In woodpecker hole high in a pine or other tree. Eggs: (1 set) 
6, pale blue. 
Food. — Largely caterpillars; also crickets, weevils, ants, moths, locusts, 
and grapes in winter months when insect food is less abundant. 
The western bluebird is often seen on roadside fences from which 
it flies down to pick up insects. In the pine woods it sits close to the 
tree trunks on short broken-off branches. It has the soft warble of 
its kind, and the delicate bluebird way of lifting the wings while 
perching. 
767a. S. m. bairdi Ridgw. Chestnut-backed Bluebird. 
Similar to occidentals, but back wholly chestnut. 
Distribution. — Transition and Canadian zones of the Rocky Mountain 
district, south to Arizona, Texas, and northwestern Mexico. 
Food. — Partly grasshoppers, weevils, crickets, and sumac berries. 
The chestnut-backed bluebird extends east as far as Pueblo, Colo¬ 
rado, during migration, and breeds from the base of the foothills 
up to 9500 feet. 
768. Sialia arctica Swains. Mountain Bluebird. 
Adult male. — Upper parts light purplish blue or greenish blue; under 
parts pale greenish blue. In winter color dulled by dull brownish tips to 
feathers above and below. Adult female: upper parts brownish gray, wings 
and tail bright blue; under parts fawn color, with blue showing through. 
