SWIFTS 351 



"White-throated Swift. Aeronautes melanoleucus (Baird) 



Field characters. — Resembling a swallow but wings much longer and more slender, 

 and tail longer; outline in flight crossbow-like. Plumage black save for white on 

 throat and mid-breast, and white patch on either side of rump. (See pi. iGg.) Flight 

 swift and erratic, with very rapid beats of the wings which at times appear to operate 

 alternately. Voice : A series of shrill twittering notes. 



Occurrence. — Summer visitant locally in small numbers Avest of the Sierran crest, 

 and belQW the Canadian Zone. Seen at Pleasant Valley and El Portal, and in Yoscmite 

 Valley. Extreme dates of observance, April 27 (1916) and September 29 (1915). 

 Courses about in the open air, usually high over sheer cliffs. 



Through our field observations we have come to associate the White- 

 throated Swift W'ith open, canons or valleys flanked by bare rocky cliffs ; 

 and as the canon of the Merced River affords locally just these conditions, 

 it was no surprise to find numbers of these birds at Pleasant Valley and 

 El Portal and in and about Yosemite Valley. 



The White-throated Swift may be distinguished from any of the 

 swallows by its crossbow-like outline of body and wings, the latter notably 

 slender, its black plumage sharply relieved by white on throat and middle 

 of breast (pi. 4:6g) and on sides of rump, and by its more reckless manner 

 of flight. Its shrill twittering notes, of insistent quality, are also different 

 from those of swallows. 



The much frequented vantage places on the walls of Yosemite Valley, 

 such as Columbia, Yosemite, Union, Sierra and Glacier points, afford good 

 places from which to see White-throated Swifts on almost any day during 

 the summer season. The birds often pass very close to an observer 

 stationed on one of these points, sometimes dashing downward into the 

 valley below at lightning speed, again pursuing a more level course with a 

 half-mile of clear air between themselves and the Valley floor. They begin 

 early in the morning and are active until late evening, even after the 

 last rays of the evening sun have left the surrounding peaks and dusk is 

 creeping into the gorge below. Thus on June 7 and again on June 23, 

 in 1915, swifts were noted still abroad in the neighborhood of the Three 

 Brothers at 7 :30 p.m. 



In all our watching of White-throated Swifts we have never seen one 

 alight on the ground or upon any sort of perching place. But on one 

 occasion, birds were seen to disappear in the face of the beetling cliff above 

 the upper zigzag on the Yosemite Point trail. Their roosting and nesting 

 places are located in narrow crevices of the rock walls, within which the 

 birds cling, and such sites are, of course, practically inaccessible to any 

 animal save the birds themselves. 



