26 BULLETIN 171, II. S. DEPARTMENT OF AGRICULTURE. 



western Montana: another subspecies, the chestnut-backed bluebird 

 (Sialia mexicana oairdi) , is a bird of the Rocky Mountain and Great 

 Basin region from Wyoming southward to northern Mexico; while 

 a third form, the San Pedro bluebird {Sialia mexicana anabelce) , 

 ranges from northern Lower California to southern California. The 

 three forms will be treated together, and for convenience referred to 

 as the western bluebird. It has the same gentle, quiet demeanor that 

 characterizes its relative of the Eastern States and, although not 

 quite so domestic, is much inclined to frequent orchards and the 

 vicinity of farm buildings. While the eastern bluebird usually nests 

 either in a hole of an orchard tree or in a box provided for its use, 

 the western species has not fully abandoned forest trees as nesting 

 sites and often may be found in lonely canyons or among hills far 

 from the abodes of man. The orchards of the west coast are hardly 

 old enough to offer many hollow trees as nesting places so attractive 

 to this gentle friend. In time, however, this bluebird will without 

 doubt become as domestic as the eastern species. In fact a nest was 

 once found by the writer in a hollow tree in the home orchard of a 

 ranch only a few rods from the house. The six young contained in 

 this nest would seem to indicate that in fecundity the western species 

 resembles its eastern cousin. 



The western bluebird is less migratory than the eastern and does 

 not entirely desert the United States in. winter; so its good work is 

 continuous. As insects are active in California in every month the 

 bird is able to support life even without other food. Moreover, the 

 bird renders a great economic service in the reduction of these pests 

 at this season, for insects that live through the winter are the stock 

 by which the species is perpetuated, and the destruction of a few at 

 this time is equivalent to the death in summer of hundreds or even 

 thousands. 



Food. — For the investigation of the food of the western bluebird 

 217 stomachs were available. While the greater portion of these 

 were collected in California a number are from Oregon, a few from 

 British Columbia, and one from Texas. Every month in the year 

 is represented, though several not so fully as desirable. The food 

 was found to consist of 81.94 per cent animal to 18.06 per cent 

 vegetable matter. 



Animal food. — Useful beetles, mostly Carabidaa, with a few lady- 

 birds (Coccinellidse), were eaten to the extent of 8.56 per cent, a 

 little less than the record of the eastern bluebird. Other beetles, all 

 more or less harmful, amount to 15.44 per cent. No special prefer- 

 ence for any family was shown. While ants constituted 5.38 per 

 cent of the food, none were found in the stomachs taken in May or 

 December, and they appear to be distributed rather irregularly; 

 July, for instance, has nearly 19 per cent, and August only 1 per 

 cent. Other Hymenoptera (wasps and bees) amount to only 1.26 



