222 UNIVERSITY OF COLORADO STUDIES 



Ixoreus naevius, Varied Thrush (763) 



The writer saw a bird of this species in Gregory Canyon, near Boulder, 

 December 5, 1909, under conditions favorable for accurate observation. It is the 

 only record for Colorado. 



Saxicola oenanthe leucorhoa, Greenland Wheatear (765a) 



Minot recorded a specimen from Boulder, May 14, 1880. Ridgway con- 

 sidered the record as probably of this subspecies with the possibility of it being 

 5. 0. oenanthe (Henderson). It is the only record for Colorado. 



Sialia sialis sialis, Bluebird (766) 



Gale found a nest with four eggs on June 18, 1887, probably in the Yellow 

 Pine zone. The bird, though rare in Colorado, apparently occurs regularly in the 

 eastern part of the state. 



Sialia mexicana bairdi, Chestnut-backed Bluebird (767a) 



Summer resident; infrequent in the Yellow Pine zone; occurs on the Plains in 

 migration. Arrives, March 31 (i~ record); leaves, September 15 — October 8 

 (4 records). Gale found two nests on June 8, 1887, one with young birds. Wid- 

 mann observed two pairs in Estes Park (7,500 feet) in 1910. 



Sialia currucoides, Mountain Bluebird (768) 



Summer resident; abundant at the western edge of the Plains and in the 

 Yellow Pine and common in the Mountain zone, occurring up to timberline. 

 Arrives on the Plains and in the mountains, February 21 — March 16 (10 records); 

 leaves, October 10-21 (4 records). Gale found many nests between May 15 and 

 June 30, and recorded one as early as April 28; his sets were taken mostly at 

 8,500 to 9,500 feet. 



Vertical Distribution 



A provisional distribution of the breeding birds and summer 

 visitants in relation to altitudinal zones is given in the following 

 tables. Species printed in italic have been found principally in 

 one zone. 



