EGGS OF NORTH AMERICAN BIRDS. 155 



blue; .68 -f- .80 to .69 -}- .81. Nests placed on the ground, 

 composed of grass, feathers, etc., liued with soft material. 

 Breeds in the Old World, and at least occasionally in Green- 

 land, Alaska, and Labrador. 



766. Bluebird, Sialia sialis. Eggs, 4 to 6, oval, pale blue 

 or occasionally white ; .62 -\- .75 to .68 -\- .80. Nests placed 

 in holes of trees or in martin boxes, composed of grass. 

 Breeds in Eastern United States, west to the base of the Rocky 

 Mountains, and from Florida north to Manitoba, Ontario, and 

 Nova Scotia, in April and May. 



766a. Azure Bluebird, Sialia sialis azurea. Eggs, indis- 

 tinguishable from those of No. 766. Breeds in Southern 

 Arizona and Eastern Mexico. 



767. Western Bluebird, Sialia mexicana. Eggs, indis- 

 tinguishable from those of No. 766, and the nests and nesting 

 habits are similar. Breeds in Western United States, from 

 the eastern base of the Rocky Mountains to the Pacific coast, 

 in March. 



768. Mountain Bluebird, Sialia arctica. Eggs, 4 or 5, 

 oval, very pale blue, size of those of No. 766. Nests placed 

 in holes of trees or in cliffs. Breeds in Western North 

 America, from the western parts of the plains to the Pacific, 

 and north to Great Slave Lake, in June. 



