SWIFTS 349 



Northern Black Swift. Cypseloides niger borealis (Kennerly) 



Field characters. — Larger than any of our swallows or the WTiite-throated Swift, but 

 resembling the latter in its long slender wings; tail very broad. Plumage black; 

 no white marks ordinarily apparent. Flight more swalloAv-like, less erratic, than that 

 of White-throated Swift. Voice: A high-pitched twitter, not so shrij] or long-continued 

 as that of White-throated Swift. 



Occurrence. — Flock of about 15 seen by us over Yosemite Valley, May 17, 1919; 

 also noted there June 17 and 18, 1920 (C. W. Michael, MS). Others seen singly or in 

 pairs by us during June and July, 1920, at Dudley, east of Coulterville. Forages in 

 the open air. 



The Northern Black Swift is a species notable, at least in California, 

 for the irregnlarity of its distribution. It is a bird often watched for 

 but seldom seen except in a very few well-known localities where it may 

 be counted upon to occur year after year. So it was a matter of genuine 

 surprise, on the morning of May 17, 1919', to see a flock of 15 of these 

 birds coursing in level formation over the dense stand of slender young 

 pines just north of Stoneman bridge. 



The first glance at the flock showed it to consist of swifts rather than 

 swallows, and then a few minutes' study disclosed many important differ- 

 ences between these birds and the smaller, better known. White-throated 

 Swift. The Black Swift is distinctly the larger, and it appears to be 

 all black except for the brownish forehead which sometimes reflects in 

 strong sunlight almost like white. The fore margin of the two wings as 

 viewed from below is a double convex, and not a single continuous arc 

 as in the White-throated Swift ; moreover, the movements of the wings 

 are more deliberate than in that species. The tail, nearly square-ended 

 in the larger swift, was broadly spread in fan shape. The birds indi- 

 vidually wove courses in and out among their companions, all remaining 

 on about the same level. None was seen to indulge in the downward 

 tumbling flight so characteristic of the smaller, pied species, nor were 

 any of the Black Swifts heard to utter notes of any kind. Our attention 

 was attracted to other birds, and a little later when looked for again the 

 big swifts were gone and were not seen at any other time during the 

 remaining week of our stay in the Valley. None was seen during any 

 of our previous visits to the region. 



On July 20, 1920, a pair of these birds was made the subject of special 

 observation at Dudley, where the species had been seen almost daily during 

 the month preceding. Sometimes the two birds were seen together but 

 more often there was one bird alone. They flew very high as a rule so 

 that it took much peering into the blue to descry them. Occasionally they 

 were heard to twitter, in a voice high-pitched but not having nearly the 



