SWAINSON HAWK. Buteo swainsoni Bonaparte

Field characters.—Similar to those for Red-tailed Hawk but size somewhat smaller and tail never red; body coloration widely variable; chin abruptly whitish, whatever the phase of color of the plumage (pl. 44h). Voice: Cry similar to that of Red-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 25, 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 (pl. 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 abrasion 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 millimeters 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 of a hit or miss process, as was evinced by the loss of these twigs and by the simple manner in which the nest twigs rested one upon another. The irregular form of the twigs doubtless serves a good office in helping to hold the structure together. A few down feathers from the adult birds clung to the leaves in the nest.

When visited on May 7 the nest contained one egg; the next morning there were two, the usual complement for this species. As the nest was approached on the second morning, one of the hawks flushed at long range from its perch in the adjacent dead tree and circled for some minutes high overhead, giving at intervals a loud prolonged cry that was clearer and more sustained than that of a Red-tailed Hawk. This bird, presumably the male, was evidently acting as 'observer'; for the mate remained on the nest until we approached within 50 feet, when it, too, took to flight. Both birds soon disappeared, and were not again seen. The area beneath the nearby dead tree was splashed with 'whitewash' (excrement), showing that it had been occupied frequently as a roost. It was doubtless the accustomed perch and lookout post for the mate of the sitting bird, and its proximity may have determined the selection of the nest tree itself.

Incidentally, it may be remarked that this perching tree of the hawks was tenanted by a pair of Plain Titmouses, with their brood of young, and a pair of Western Bluebirds with a completed set of eggs; while a likely looking hole higher up was being prospected by a pair of Violet-green Swallows. The close proximity of this pair of birds of prey, representatives of a species which rarely if ever eats small birds, was evidently of no more concern to the titmouses and bluebirds than would have been the presence of a pair of California Woodpeckers within similarly close range.

A Swainson Hawk observed in flight showed a light throat (pl. 44h), dark chest, rather narrow but bluntly ended wings, and a light patch at the side of the rump. All of these points aided in differentiating the bird from the Red-tailed Hawk. Of course, there is no red on the tail of the Swainson at any age. In motion this bird's wing-beats are quicker and more frequent than those of the Red-tail.