IQ4 UNIVERSITY OF COLORADO STUDIES 



Buteo borealis calurus, Western Red-tail (337ft) 



Permanent resident; common in the summer from Plains to Mountain zone. 

 Infrequent in the winter, when it is apparently confined to the Plains. Arrives in 

 migration in March and is most numerous in September and October. Gale found 

 eggs on the Plains and in the Mountain zone from May 26 to June 3. 



Buteo swainsoni, Swainson's Hawk (342) 



Permanent resident ; common on the Plains. There appear to be no definite 

 records for the mountains of the county, though Widmann recorded one at Estes 

 Park on June 12, 1910. It is infrequent in winter. On September 15, 1912, the 

 writer observed a flock of about fifty birds on the open plains near Boulder, many 

 of which appeared to be catching grasshoppers. Gale found nests between May 

 12 and June 10. 



Archibuteo lagopus sancti-johannis, Rough-legged Hawk (347a) 



Winter resident; common on the Plains. It occurs in the Yellow Pine zone 

 in migration at least. Arrives, October 15-30 (2 records), and leaves, March 

 I 4 - 3 I (3 records). One in the University collection was taken February 10, 1910. 



Archibuteo ferrugineus, Ferruginous Rough-leg (348) 



Summer resident; infrequent. Probably common during migration. Gale 

 listed it as wintering on the Plains but does not mention the species further in his 

 notes. Two specimens in the University collection are labelled March 27 and 

 August 16. There are no nesting records for the county, but birds were seen by 

 the writer July 29, 1911, in the Mountain zone. Pierce (Kellogg) reported the 

 species common at Estes Park and Widmann saw two specimens there June 10, 

 1910. 

 Aquila chrysaetos, Golden Eagle (349) 



Permanent resident; rather infrequent. Occasionally reaches the Plains 

 zone but most frequently reported from the Yellow Pine. Gale took several sets 

 of eggs between March 21 and April n. A pair nested on the cliffs at Left Hand 

 Creek in 1912. Kellogg reported a pair at Specimen Mountain (near the range in 

 Estes Park). 

 Haliaeetus leucocephalus leucocephalus, Bald Eagle (352) 



Migrant; rare; recorded from Plains and Yellow Pine zones. Henderson 

 records one seen by himself and one seen by Blanchard. The writer saw two 

 December 5, 1909, and one March 17, 1912. Kellogg (1889) recorded one from 

 Estes Park. 



Family FALCONIDAE, The Falcons, etc. 

 Faleo mexicanus, Prairie Falcon (355) 



Summer resident; probably infrequent. Gale twice found it nesting along 

 the St. Vrain, apparently in the Yellow Pine zone (May 4, 1893; May 7, 1899), 



