226 UNIVERSITY OF COLORADO STUDIES 



TABLE IV 



Breeding Birds Occurring in the Alpine Zone, above 11,500 Feet 



Total, 5 Characteristic, 3 



White-tailed Ptarmigan* White-crowned Sparrow 



Desert Horned Lark Pipit 



Brown-capped Rosy Finch 



* Species printed in italic have been found chiefly in this zone. 



It is interesting to note that the following fifteen species, which 

 occur in all the zones of the county except the Alpine, range according 

 to the A.O.U. Check-List from the southern boundary of the United 

 States to the provinces of Mackenzie, Yukon, and northern Alberta 

 in Canada (except that the subspecific forms of the Nighthawk, Red- 

 wing and Robin change in the most northern part of their range) : 



Spotted Sandpiper Brewer's Blackbird 



Western Red-tail Pine Siskin 



Belted Kingfisher Western Chipping Sparrow 



Red-shafted Flicker Barn Swallow 



Western Nighthawk Western Warbling Vireo 



Western Wood Pewee Western House Wren 



Magpie Western Robin 



Thick-billed Red-wing 



The Broad-tailed Hummingbird, however, which is common in the 

 Mountain zone and found even at timberline, ranges north only to 

 southern Idaho. 



The data on the altitudinal limits of the breeding ranges are hardly 

 exact enough in the majority of cases to make an extended comparison 

 between vertical and latitudinal range of much value at present. A 

 careful study of that nature should, however, prove quite interesting 

 in connection with the proper limits of the life-zones. 



Local Migration Problems 



A number of points in connection with the influence on local migra- 

 tion of the mountain ranges, and of the comparatively short seasons 

 at the high altitudes, are of considerable interest. On account of 



