182 UNIVERSITY OF COLORADO STUDIES 



While lodgepole pine and Engehnann spruce frequently occur in the 

 same stand of timber, pure forests of lodgepole are found only in the 

 lower part of the zone. So far as bird-life is concerned, the lodgepole 

 forests serve to separate the dry and open yellow pine region from the 

 moister spruce and fir forests. Aspen groves are frequent in the lower 

 part of the zone, in the forest and along the borders of parks and near 

 mountain meadows. Glacial lakes, frequently enlarged for reservoir 

 purposes, are common higher up, at elevations of about 10,000 feet 

 and higher. 



The Alpine Zone embraces the area above timberline. The highest 

 altitudes reached are Long's Peak, 14,271; Arapahoe Peak, 13,320; 

 and Mt. Audubon, over 13,000 feet. Dwarf willows penetrate the 

 zone here and there along the courses of streams from the perennial 

 snow banks. In general, the region is rocky with vegetation in 

 patches which decrease in area to mere pockets among the rocks along 

 the crest of the range. 



The accompanying map is based on the Topographic Map pre- 

 pared in 191 2 by the State Geologist of Colorado. It shows the 

 position of Boulder County in relation to the Continental Divide, 

 Barr Lakes, Estes Park and Tolland (in Boulder Park). The dotted 

 contour lines at 6,000, 8,500 and 11,000 feet divide the county roughly 

 into the zones just described. 



Annotated List of Birds of Boulder County 



The following list is printed in two styles of type. Birds that are 

 regarded as of regular occurrence are in bold-face. Italic is used for 

 the species whose claim to a place in the bird-life of the region rests 

 on so few records that their occurrence in the future would be expected 

 only as an accident of migration, or whose status has not been fully 

 determined. Hypothetical species are inclosed in brackets. 



There have been difficulties in deciding just what number of records 

 make a bird "regular in occurrence," especially in view of the fact 

 that the normal number of individuals for a species in any given region 

 is so variable. It has been the intention to indicate as "regular" all the 

 species credited to the county whose records suggest that they would 



