290 ANIMAL LIFE IN THE YOSEMITE 



SwAiNSON Hawk. Buteo swainsoni Bonaparte 



Field characters. — Similar to those for Ked-tailed Hawk but size somewhat smaller 

 and tail never red; body coloration M-idely variable; chin abruptly whitish, whatever the 

 phase of color of the plumage (pi. 4ih). Voice: Cry similar to that of Eed-tail but 

 clearer and more prolonged. 



Occurrence. — Summer visitant in small numbers both east and west of Sierra Nevada. 

 Found near Lagrange, May 8, 1919 (nest with two eggs), and near Williams Butte, 

 May 12 and June 2-5, 1916 (specimens). 



The Swainson Hawk seems to be local in its distribution in the Yosemite 

 region, for, as we note above, it was seen by us on only three occasions. 

 Yet in certain places elsewhere in California it is the commonest of hawks. 

 This is the only species of hawk in our region which migrates south entirely 

 out of the state for the winter months. Its normal breeding range involves 

 only the Upper Sonoran and Transition life zones, and the records given 

 above were from within those zones. Elsewhere in the Sierra Nevada 

 during the fall months this bird has been known to wander up to the higher 

 altitudes, even to the Hudsonian Zone, but we saw none during the several 

 months we spent in the higher portions of the Yosemite region. 



In one of the numerous large blue oaks which dot the Upper Sonoran 

 hills about Lagrange a nest of this species was found on May 7, 1919, and 

 the next day we visited it for detailed study. The nest tree was on the 

 crown of a hill and therefore it and the adjacent dead 'perching tree,' 

 about 20 feet off, both commanded view over a wide range of country. 

 The top of the nest was 7 meters (nearly 24 feet) above the ground and 

 close to the top of a vigorous blue oak. The nest was built on a slanting 

 branch 120 millimeters in diameter. At this point the branch forked, each 

 of the subsidiary branches being about 85 millimeters through; there was 

 no other support. The nest proper (pi. 45a) was of dead blue oak twigs 

 4 to 15 millimeters in diameter and 200 to 750 millimeters in length, most 

 of the pieces being very crooked. Many of the twigs showed abra-sion 

 where they had been grasped midway of their length by the hawks when 

 building. A few fresh twigs, with leaves still attached to them, were 

 included in the framework of the nest. Within this coarser structure there 

 was a lining composed chiefly of green blue oak leaves (actually twig ends 

 with new leaves of the current season's growth), and a small amount of 

 foxtail grass. The nest measured, outside, about 550 by 750 millimeters 

 and its greatest height was about 200 millimeters ; the leafy depression 

 was 200 by 250 millimeters across and at the center was about 100 milli- 

 meters below the rim of the nest. Below the nest, lodged in the lower 

 branches of the tree were numerous twigs, evidently dropped during the 

 construction of the nest. Building the nest was probably more or less 



