232 BULLETIN 16 7, UNITED STATES NATIONAL MUSEUM 



feathers. I have seen a pair of these hawks show as much resentment 

 at the invasion of such a domain as they do when a nest is ap- 

 proached. As it launches into flight, or rises from the ground, this 

 hawk appears awkward and heavy, but when well under way, its 

 flight is strong and graceful, as it sails upward in great spirals until 

 almost out of sight. It has all the full flight powers of the best of 

 the Buteos. Facing a strong wind it can hang almost motionless or 

 glide swiftly down a long incline. A pair often indulge in graceful 

 evolutions, apparently in play or for exercise. Migrating flocks often 

 move along in a series of long ellipses. 



Voice. — ^I recorded the cry of Swainson's hawk as a prolonged, 

 shrill, somewhat plaintive whistle, kree-e-e-e, suggestive of the cry 

 of the broad-winged hawk, but not so prolonged and not so plaintive. 

 The call is given while the hawk is in flight or while perched on a 

 tree. Taylor and Shaw (1927) describe the notes as follows: "One 

 call of the Swainson hawk was set down as a loud squeeuk! Another 

 call note closely resembles the peear! of the western red-tail. The 

 loud scream-call is often followed by a series of strongly whistled 

 syllables resembling tsip! tsip! tsip! tsipP'' 



Mr. Cameron (1913) says of the voice of the young bird: 



The j'oung buzziird's cry differed according to his age. When he was quite 

 young it resembled a kitten as stated, but by the end of August, when he was 

 seven weeks old, it became loud and shrill like the scream of a sea-gull, though 

 more piercing. At two months old he developed a musical cry, the appealing 

 tone of which never failed to create a deep impression upon all who heard it. 

 It consisted of four notes insistently repeated like E U, E U, the second E 

 being a half tone lower than the first, and may be described as long sustained 

 wails followed by short staccato notes. While these four notes are difficult to 

 express in words they could be easily reproduced upon the violin, and are not 

 unlike the plaintive but shriller tones of the British Lapwing {VaneUus vanel- 

 lus) when hovering over its breeding grounds. 



Field marks. — In the normal adult, or common, light phase of 

 plumage, Swainson's hawk is easily recognized by the color pattern 

 of the under parts, pure white throat and belly, broad chest band of 

 dull brown, grayish tail, with many narrow bands, and the unmarked 

 buffy under wing coverts. Immature birds, mehinistic birds, and 

 birds in the many intermediate stages and phases are very difficult 

 to recognize, except by a process of elimination. Young birds are 

 generally darker below than other young Buteos and show a sugges- 

 tion of the adult color pattern. Erythristic and partially melanistic 

 birds often show a similar suggestion. The wings are narrower and 

 slightly more pointed than the redtail's; the wing beats are some- 

 what quicker and more frequent; and there are light patches on the 

 sides of the rump. 



Fall. — Late in August Swainson's hawks gather into large flocks, 

 wheeling and circling high in the air as they gradually drift south- 



