NORTHERN BLACK SWIFT. Cypseloides niger borealis (Kennerly)

Field characters.—Larger than any of our swallows or the White-throated Swift, but resembling the latter in its long slender wings; tail very broad. Plumage black; no white marks ordinarily apparent. Flight more swallow-like, less erratic, than that of White-throated Swift. Voice: A high-pitched twitter, not so shrill 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 irregularity 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 differences 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 individually 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 piercing quality characteristic of the White-throated Swift. There was much sailing along on set wings; when the wings were flapped the beating was slower than it is in either the White-throated or the Vaux Swift. When the birds were at certain angles from the observer, striking flashes of silvery gray were given off from the wings.

Mr. Donald D. McLean believes that the Northern Black Swifts nest in this vicinity in burned-out black oak stubs; and he may be right. There are no rock cliffs short of ten miles away; and he says the swifts have been about the locality each summer ever since he can remember. He occasionally sees one bird of a pair dart down from a great height, always to disappear beyond some ridge or behind some large tree. He showed one of us a prostrate hollow oak about which, before it fell, he says these swifts used to be seen; but he never saw a bird actually enter a cavity. With this hint, someone, sometime, with a stock of time, patience, and favoring luck, may enjoy the thrill of the actual discovery of a Black Swift's nest in the Yosemite region.

W. O. Emerson (1893, p. 179) recorded the Northern Black Swift as "very common high up in all the cliffs, particularly [along] the face of Glacier Point" in June, 1893.