62 Lincoln, Birds of the Clear Creek District, Colo. [j a u n 



The western edge of the district is marked by the Yellow Pine 

 covered foothills, supporting many forms that wander into the 

 valley after nesting time or follow it as a migrational highway. 1 



North of the mouth of Clear Creek Canyon about eight miles, 

 Ralston Creek, a left-hand tributary, leaves the foothills. This 

 stream is small but deep and sluggish, and scantily wooded. After 

 flowing past the Leyden mines it enters Clear Creek valley but 

 nevertheless, maintains some semblance of an individual valley 

 for several miles. Passing through the town of Arvada, it empties 

 into Clear Creek a few miles above the junction of the latter with 

 the South Platte River. 



At irregular intervals, on both the north and south slopes of the 

 valley, are numerous natural lakes, many of which are now put to 

 practical uses, principally irrigation. Two, on the south slope, at 

 the suburban town of Berkeley, are passed regularly in going to and 

 from the lower valley on the interurban electric railway, and 

 although the interval when they may be scanned for birds is brief, 

 they have nevertheless, been the means of adding a few species to 

 the list. Such records will be noted as " the lakes at Berkeley." 



Another lake, on the north slope of the valley, known locally as 

 Mud Lake, has also been visited spasmodically, and has yielded 

 an additional portion. 



Systematic work by the writer was begun in the spring of 1908. 

 One day trips were made regularly, the average for 1910, 1911, 

 and 1912 being thirty-five to the year, or of greater frequency than 

 one each two weeks. During migrations they were made at least 

 weekly, and occasionally semi-weekly, the longer intervals falling 

 in the mid-summer and winter periods. An endeavor was made 

 to render a complete record of breeding activities, by establishing 

 permanent camps during June 1909, and June 1910, with an addi- 

 tional camp in the fall of the latter year. The total result of these 

 operations is a number and variety of forms hardly to be expected 

 in such a limited area. 



1 This country to the west has been ably treated by Messrs. R. B. Rockwell and Alex- 

 ander Wetmore. (Auk, Vol. XXXI, No. 3, ' A List of Birds from the Vicinity of Golden 

 Colorado.' The present writer periodically visited this country (together with the Hog- 

 back ridge to the south) and secured species not recorded in the above mentioned paper. 

 They will accordingly be incorporated in this list with due reference to the locality. F. C. L. 



