CHECK-LIST OF COLORADO BIRDS 345 



76 1. American robin. MERULA MIGRATORIA. Summer 

 resident, but not common ; some interesting questions 

 arise in connection with intermediate forms. 



76la. Western robin. MERULA MIGRATORIA PROPINQUA. 

 Abundant summer resident ; breeds from plains to timber- 

 line. 



765a. Greenland wheatear. SAXICOLA (ENANTHE LEUCO- 

 RHOA. European species ; a straggler taken at Boulder by 

 Minot. 



766. Bluebird. SIALIA SIALIS. Rare summer resident ; 

 west to base of Rockies. 



767a. Chestnut-backed bluebird. SIALIA MEXICANA 

 BAIRDI. Summer resident ; not common ; western form, 

 coming east as far as Pueblo. 



768. Mountain bluebird. SIALIA ARCTICA. Abundant 

 summer resident ; breeds from plains to timber-line ; in 

 autumn roams up to at least 13,000 feet. 



