MOUNTAIN BLUEBIRD 285 



sites, notably flickers and English sparrows, and probably the ordinary 

 predators take their toll. Mr. Criddle (1927) says of these two 

 enemies: "Flickers are quite important factors in the survival of 

 young bluebirds, even though they often provide the adults with 

 nesting holes. Two instances came to my attention of the parents 

 being driven from their nests by flickers, in both cases resulting in 

 the deaths of the young by starvation. * * * Male mountain 

 bluebirds are able to defend their nests against all intruders of their 

 own size, this includes the house sparrow which has somewhat of a 

 reputation for ousting other species. The sparrow, however, is no 

 match for the bluebird in open fight and despite its persistency, it has 

 never been observed to get possession of a nesting box occupied by 

 the latter." He has seen the bluebirds drive away kingbirds, crows, 

 and squirrels, but the flickers are generally too formidable. House 

 wrens have nested near the bluebirds, but he has never seen the former 

 do any damage to the latter. Among the enemies of the bluebirds he 

 mentions Cooper's and sharp-shinned hawks and weasels but thinks 

 the latter are not so destructive as the squirrels, which are better 

 climbers. Cold rain and snowstorms early in spring or late in fall 

 often prove fatal to young, or even adults. 



Dr. Friedmann (1938) could find only one record of cowbird para- 

 sitism; a nest found by T. E. Randall in Alberta contained four eggs 

 of the bluebird and one of the Nevada cowbird. 



Fall. — Early in August, family parties begin to gather into small 

 companies or larger flocks and gradually drift along southward from 

 the more northern portions of their summer range, the migration con- 

 tinuing well into November. They do not ordinarily move in com- 

 pact flocks. At this season one often sees detached companies of 

 mountain, western, or chestnut-backed bluebirds wandering about the 

 open country, sometimes loosely associated with sparrows, juncos, 

 warblers, flickers, and other small birds, on their way south. But 

 many bluebirds spend the winter in the greater part of their summer 

 range, moving from the mountains down into the valleys. 



Winter. — Ralph Hoffmann (1927) says: "In winter any extensive 

 open country, such as the wheat fields of interior California, is visited 

 by flocks of mountain bluebirds." 



These bluebirds do not wholly desert the higher elevations even in 

 winter; Russell K. Grater writes to me: "During late February 1942, 

 I had occasion to be on ski patrol into Cedar Breaks National Monu- 

 ment. At that time the snow was several feet deep on the open. 

 The altitude is around 10,300 feet. Here on the snow fields were 

 many mountain bluebirds, darting hither and yon, apparently catch- 

 ing something on the snow. An investigation revealed that the snow 

 was literally alive with hundreds of tiny winged insects and the birds 



