AN ANNOTATED LIST OF THE BIRDS OF 

 BOULDER COUNTY, COLORADO 



By Junius Henderson 



Boulder County is a well-settled county, compared with some others 

 of the state, and in its midst is situated the University of Colorado, with 

 its rapidly increasing student body, therefore it appears to deserve a 

 carefully prepared bird list. The present paper gives the results of 

 seventeen years' study of the county's avifauna and the literature bearing 

 thereon. Not being an ornithologist, these notes contain only such 

 information as the writer has been able to gather while in the field 

 engaged in paleontological and conchological investigation, supple- 

 mented by access to the notes, published and unpublished, of others. 



Boulder County is approximately twenty-four miles wide (north- 

 south) and about 32 miles long (east-west). The western edge follows 

 the irregular crest of the Continental Divide, the highest point being 

 Long's Peak, in the extreme northwest corner, 14,271 feet above the 

 sea according to the "Hayden Survey," more recent surveys slightly, 

 but not materially, changing those figures; the lowest point, near the 

 eastern boundary, being about 5,000 feet. There is thus presented a 

 difference of about 9,000 feet between extremes of altitude, with corre- 

 sponding differences in temperature, humidity, atmospheric density, 

 vegetation, etc. Nearly the western two-thirds of the county is moun- 

 tainous, the remainder forming a portion of the western edge of the 

 Central Great Plains, locally called "the valley" to distinguish it from 

 the mountainous area. Both areas present a great variety of conditions 

 aside from mere differences in altitude, from which a varied avifauna 

 would be expected. It is therefore an ideal field for the student of 

 ornithology. 



The formerly semi-arid plains area has been, to a great extent, 

 transformed into irrigated and cultivated fields, though tracts of con- 

 siderable size above the convenient reach of ditches on the divides 

 between streams still remain dry, treeless, shrubless prairie. Four 

 principal streams and several minor ones, issuing from the mountain 



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