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May, 1918 THE WHITI?-TttROATI?D SWIFT IN COLORADO 107 could not be reached from this bench, nor was there any secure footing on which the ladder, after being drawn to the third lift, could be placed so as to reach the diagonal crevice to be explored. However, after securing the best rest possible for the upper end, the lower extremity was supported by two men on the insecure footing available, while the third man carefully climbed to the crack in the rock. From this point, and without any disaster, he secured nest number two, with four nearly fresh eggs, placed about two feet back in the crevice. (See fig. 16.) While watching and admiring the powerful, graceful, and apparently ef- fortless flight of these unrivalled masters of the air, I noticed what appeared to be a conflict in midair, in which two birds clinched, fluttered, and fell as if with broken wing, ten or twenty feet before separating. I had heard of their copulating in flight, but was still somewhat skeptical. Neidrach assured me, however, that he had frequently noticed this while in company with Mr. F. C. Lin- coln, Curator of Ornithology, Colorado Museum of Natural History, who had taken them in the act. Mr. Lincoln veri- fies this statement and adds that in May, 1915, while on a collecting trip in the Paradox Valley, Colorado, he frequently observed this curious action. On two oc- casions he collected with a single shot the ?wo birds while in the act, and both times one proved to be a male, the other a fe- male. Examination of the sexual organs showed them to be in full breeding condi- tion. The difference of about a month be- tween the date of his observations and ?ny .., own is accounted for by the difference in seasons, altitude and latitude. The balance of the four days we spent at these cliffs was much a repeti- tion of the foregoing, the nest sites dis- covered being protected by overhanging Fig. 17. F?rT PEET raoa? THE Bcrr- TOiVI, BUT UNABLE TO REACtI NEST projections and mostly on the sides of SITE BENEATtI PROJECTING BOCK. inaccessible pinnacles. In one instance one was located on the face of the main bluff back of some steeples, perhaps one hundred feet below the mesa above, and thirty feet above the top of a chim- ney slide, to which one of the boys laboriously climbed. We anchored and low- ered the swing outfit with a view of raising him to the nest, but the swing in passing the projections, and the manipulation of the rope afterwards, contin- ued displacing such volumes of loose materials that it would have been suicidal to have attempted reaching the nest. A Raven's nest and also a Red-tailed Hawk's nest, similarly located at different points on the main cliff, were aban- doned for the same reason. This year (1917), with three assistants, I revisited this same site by auto- mobile, when a day and a half of hard and conscientious work was but a repe- tition of the foregoing experience, except-that no nests located could be reached from below or above, and none was taken. On my return to Denver,