BIRDS OF BOULDER COUNTY, COLORADO 201 



Tyrannus verticalis, Arkansas Kingbird (447) 



Summer resident; while common on the Plains during migration, this species 

 is infrequent in summer and confined to the dry eastern portion of the county. 

 Arrives, May 5-18 (3 records); leaves, August 21-29 (3 records). Eggs were 

 found by Gale from June 1 to 18 (8 records). Pierce (Kellogg) reported it as rare 

 at Estes Park. 



Tyrannus vociferans, Cassin's Kingbird (448) 



One was taken by A. Mackenzie in Gregory Canyon near Boulder on Septem- 

 ber 28, 1904. Kellogg (1889) reported it as common in Estes Park; apparently 

 not since reported from there. 



Sayornis sayus, Say's Phoebe (457) 



Summer resident ; common on the Plains and infrequent in the Yellow Pine 

 zone. Arrives, April 4-9 (4 records) ; leaves, September 10-28 (3 records). Eggs 

 have been found June 8 and 23 (Henderson and Gale, 2 records). 



Nuttallornis borealis, Olive-sided Flycatcher (459) 



Summer resident; common in the upper part of the Yellow Pine and the 

 lower part of the Mountain zone. Arrives, May 18 (1 record) ; leaves, August 

 28 (1 record). Gale found eggs (first hatching) between June 22 and July 8, at 

 about 8,000 to 9,500 feet. 



Myiochanes richardsoni richardsoni, Western Wood Pewee (462) 



Summer resident ; common in the Plains, Yellow Pine and lower part of the 

 Mountain zone. Arrives, May 8-18 (3 records); leaves, August 26 — September 

 12 (3 records). Eggs have been found June 21 and July 12 (Gale, 2 records). 



Empidonax dirficilis difficilis, Western Flycatcher (464) 



Summer resident; common in the upper part of the Yellow Pine and the 

 lower part of the Mountain zone. Arrival, not determined; latest fall date, 

 September 10. Gale found eggs from June 12 to July 4, at elevations from 

 8,500 to 10,000 feet. The nests were practically all placed on rocky ledges or 

 the sides of prospect tunnels or shafts. Widmann found the species at several 

 places in Estes Park (7,500 feet). 



Empidonax trailli trailli, Traill's Flycatcher (466) 



Summer resident; common on the Plains (and probably extending to some 

 extent up the creeks into the Yellow Pine). Gale found eggs from June 3 to July 3. 

 The nests were in low bushes near creeks and were "invariably pensile." 



[Empidonax minimus, Least Flycatcher (467)] 



In Gale's notes casual mention is made of finding a nest of this species with 

 four eggs on June 26, 1890, apparently near Duck Lake. Other notes, however, 



