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May, 1918 THE WHITE-THROATED SWIFT IN COLORADO 105 The cliffs where the birds were seen, bordering the Grand River, east of Sulphur Springs, are of a mixed lava formation, with some parts of hard, ring- ing material, and others of cracked, crumbling formation, intermixed with seams and deposits of soft lava ash, through which the river has cut its way in ages past. The visible base of the cliffs is at the top of a steep slope of debris, extending to the Grand River several hundred feet below (see fig. 13). The mesa above the cliffs is open rolling country covered with sage brush and na- tive grass. The day following our arrival we felt our way carefully around the base of the bluffs, at times starting displace- ments of rock that rolled, bounded and smashed their way to the foot of the slope below us. In the air there was an abundance of Cliff Swallows, inter- mixed with a number of Violet-greens and an occasional Swift; and we were, of course, constantly watching the last mentioned, alert to locate their entrance to and departure from crevices indi- cating nest sites. Several of these en- trances were spotted which were inac- cessible from above, owing not only to the extremely rotten and treacherous character of the surrounding material, but also to the fact that they were plac- ed in steeples or pinnacles, separated from the main bluff. Crevices selected for nesting sites on the sides of these steeples were generally overhung by projecting rock. (See fig. 14.) The first available prospect, located by Niedrach through the presence of excrement about eight feet up, and to which he was able to climb, was in a horizontal crevice about two and one- half inches in width, sloping slightly downward and partly filled, in places, with lava, sand and vegetable matter evidently deposited by the wind (see fig. 15). Upon reaching the crevice a Swift darted forth nearly in his face, and he caught site of its mate retreating Fig. 15. NESTJNG CREVICE OF WI?ITE- TItROATED SWIFT? SI?OWING METIIOD OF GAINI?NG ACCESS. back into the crevice, from which it was not seen to emerge. Less than an hour's work resulted in collecting, from a point about eighteen inches back, our first nest, containing four fresh eggs. This seemed so "dead easy" that we were greatly encouraged, and we soon spotted a second prospect in a nearly vertical crevice about ten feet up in a V- shaped chimney. This was overhung with suqh suspiciously loose looking ma- terial that we brought a couple of long cotton-wood fence rails from the river bank below and pried loose several hundred pounds of rock, large chunks of