THE BIRD BOOK 
766. Bluebird. Sialia sialis sialis. 
Range. — Eastern United States, breeding from the Gulf to southern Canada. 
Winters in the southern half of the United States. 
These familiar birds build in cavities in trees, 
usually below 20 feet from the ground, crev- 
ices among ledges, bird boxes and in any suit- 
able nook they may discover about buildings, 
providing that English Sparrows do not molest 
them. They raise several 
broods a year, commencing in 
April when they lay from 
three to six pale bluish white 
eggs (rarely pure white) ; 
size .80 x .60. The cavities 
T , , of their nesting sites are lined 
Bluish White w jth grasses an( j feathers 
usually, although I have found the eggs on 
the unlined bottom of cavities in trees. 
766a. Azure Bluebird. Sialia sialis 
fulva. 
Range. — This pale variety is found in south- 
ern Arizona and southward. 
Its nesting habits are the same and the eggs 
are indistinguishable from the last. 
767. Western Bluebird. Sialia mexicana occidentalis. 
Range. — Pacific coast from Lower California to British Columbia. 
The Western Bluebird is as common and familiar in its range as the common 
Bluebird is in the east. It nests in similar locations and its eggs are scarcely 
distinguishable, although averaging a trifle darker in shade; size .80 x .60. 
767a. Chestnut-backed Bluebird. Sialia mexicana bairdi. 
Range. — Rocky Mountain region from Mexico to Wyoming. 
The nesting habits or eggs of this brighter colored bird do not differ from 
those of the last species. 
767b. San Pedro Bluebird. Sialia mexicana anabelae. 
Range. — San Pedro Martir Mountains in Lower California. 
The eggs of this variety will not in all probability be any different from those 
of the preceding Bluebirds. 
768. Mountain Bluebird. Sialia currucoides. 
Range. — Rocky Mountatin region, breeding from New Mexico north to Great 
Slave Lake; winters in southwestern United States and Mexico. 
This azure blue species is common in the greater part of its range and is found 
west to the Sierra Nevadas in California. Like the eastern Bluebird they nest 
in holes in trees or anywhere that they can find a suitable cavity or crevice. 
Their eggs are slightly larger than those of the other Bluebirds and have a 
slight greenish tint; size .85 x .64. 
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