264 BULLETIN 19 6, UNITED STATES NATIONAL MUSEUM 



for the evening of August 12th a small flock was seen flying overhead near the 

 base of the mountains. 



Russell K. Grater has sent me the following interesting note from 

 Zion National Park, Utah: "This bird is a summer resident above 

 7,500 feet and is commonly seen in the open forest glades near meadows. 

 Usually they range in groups of six or more before and after the nesting 

 season. In winter they drift down from the highlands into the canyon 

 bottoms but always prefer wide canyons with some open areas. 

 Frequently they are found drifting through the pifion-pine-jiiniper 

 forest, where they eat extensively of the fruit of the mistletoe. Some 

 birds, when collected, had no other undigested food except the mistle- 

 toe. Nests have been found in hollow trees, usually about 7 to 15 feet 

 from the ground. Eggs are laid in May and June and two broods are 

 not infrequent. A nesting record of more than passing interest was 

 recorded while I was living at Grand Canyon National Park. In 

 May 1935 a hollow in an old pifion pine was utilized as a nesting site 

 by both a chestnut-backed bluebird and a black-eared nuthatch. 

 Both birds would occupy the hollow at the same time, sitting side by 

 side. Each bird apparently fed only her own brood, and two families 

 were raised by each set of parents during the summer. These birds 

 were quite tame and were not at all disturbed when the hole into the 

 hollow was enlarged sufficiently for a study of this unusual event. 

 Careful records of the event were kept by more than one interested 

 bird student at the park. This is the most unusual bird relationship 

 thus far observed at Grand Canyon." 



The chestnut-backed bluebird nests also in old woodpecker holes 

 and in bird boxes, lays from four to six eggs, and in all other respects 

 does not differ materiall} 7 from the western bluebird, which is treated 

 more fully on the foMowing pages. Dr. rriedmann (1929) Lists this 

 bluebird as a very rare victim of the dwarf cowbird. 



The measurements of 30 eggs average 21.5 by 15.9 millimeters; the 

 eggs showing the four extremes measure 23.6 by 16.5, 23.4 by 16.8, 

 19.7 by 15.1, and 20.0 by 15.0 millimeters. 



DISTRIBUTION 



Range. — "Western North America from southwestern Canada to 

 central Mexico. 



Breeding range. — The bluebird of the mexicana group breeds north 

 to southern British Columbia (Beaver Creek. Vancouver Island, Alta 

 Lake, 150 Mile House, Edge wood, and Newgate). East to southeastern 

 British Columbia (Newgate); western Montana (Fortine, Columbia 

 Falls, Lolo, and Laurel); western Wyoming (Yellowstone Park and 

 Pinedale); central Colorado (Estes Park, Golden, Colorado Springs, 

 "Wet Mountains, and Fort Garland); central New Mexico (Truchas 





