500 Colorado College Publication 



departs the last of October (one specimen in the Aiken Col- 

 lection taken October 28, 1872). Occasionally winters: one 

 noted by Aiken, February 2, 1899. 



One of our most common hawks, found everywhere dur- 

 ing migration, but breeds in the mountains from the foothills 

 upward. A very valuable bird economically as its food is 

 largely mice and ground squirrels, and in spite of its common 

 name of "Hen Hawk" it attacks poultry but little. It will kill 

 animals as large as cottontails, and one was seen by Shaw near 

 Crystal Park carrying a rabbit in its talons. 



Buteo swainsoni. Swainson's Hawk. 



Summer resident; common. Arrives in March and de- 

 parts in August and September. 



This is one of the most characteristic birds of the arid 

 plains; a few go into the mountains, and there are several 

 records of its breeding at high altitudes in various parts of the 

 State, but we have no such records for El Paso County, as 

 the portion of the range within our limits presents no open 

 park-like areas such as they would likely prefer. They build 

 their nests in the cottonwood trees bordering prairie streams 

 or dry sand creeks. The nests are of moderate size, con- 

 structed mostly of coarse dead twigs and placed usually 12 to 

 15 feet above the ground; however, Aiken found one nest in 

 1878 on Horse Creek at an elevation of only six feet. On this 

 occasion 8 or 10 nests were found in which laying had com- 

 menced in only three by May 17th. He found a newly fin- 

 ished nest without eggs June 4, 1898, near Calhan, and one 

 May 15, 1904, at Ramah, which already held the full com- 

 plement of three eggs. We may therefore state that laying 

 takes place between May 10 and June 10. 



Swainson's Hawk has the rather singular habit of placing 

 two or three green cottonwood twigs with green leaves across 

 the nest. These are placed in newly finished nests before any 



