As far as my own observations go, healthy, smooth-barked aspens are always selected as suitable nesting sites by these birds. The trees used vary from 12 to 18 inches in diameter near the ground, and taper very gradually. The cavity is usually excavated below the first limb of the tree, say from 15 to 25 feet from the ground. The entrance hole seems to be ridiculously small for the size of the bird--perfectly circular, from 1¼ to 1½ inches in diameter only--so small, indeed, that it seems as if it took considerable effort for the bird to squeeze himself in and wriggle out of the hole. The gourd-shaped excavation varies in depth from 6 to 10 inches, and it is from 3 inches near the top to 4 or 5 inches wide at the bottom. The finer chips are allowed to remain in the bottom, forming the nest proper, on which the eggs are deposited. Frequently they are more than half covered by these chips. The interior of the entire excavation is most carefully smoothed off, which must consume considerable time, considering the tough, stringy, and elastic nature of the wood when filled with sap, making it even more difficult to work when partly decayed, which seems to be the case with nearly all the aspens of any size. Probably eight or ten days are consumed in excavating a satisfactory nesting site. All the larger and coarser chips are dropped out of the hole and scattered about the base of the tree. Johnson A. Neff (1928) says: “The nests of these birds are placed in whatever trees are abundant in their vicinity. In Klamath County, in the foothills and in the lower valleys, alders, cottonwoods and aspens were utilized; in the higher altitudes, firs were the common site, with the alder and willow along the small streams. In the Willamette Valley the firs, cottonwoods, willows, alders, and others, are used indiscriminately.” Near Blaine, Wash., Mr. Dawson (Dawson and Bowles, 1909) found an almost inaccessible nest of this sapsucker 50 feet from the ground in a big fir stub, “sixteen feet around at the base, above the root bulge, and perfectly desolate of limbs.” He managed to reach the nest with the help of a rope and cleats nailed on the barkless trunk. He says: “By the time I had a hole large enough to thrust in the hand, the eggs were quite buried in chips and rotten wood. But when they were uncovered, they were seen to lie, seven of them, in two regular lines, four in the front rank with sides touching evenly, and three in the rear with points dove-tailed between.”