The nests were small and compact and well hidden in their cavity. Only twice did protruding material betray the location. In one case nesting material protruded from a woodpecker hole, and the other was a bulky nest that showed from each side of a split branch. This last nest I thought must belong to a House Finch, but investigation showed warbler ownership. Nests were made of bark, weeds, and mesquite leaf-stems, and lined with fine bark, horse and cow hair, a few feathers and sometimes a little rabbit fur. The site averaged six and one-half feet from the ground, the lowest being 18 inches and the highest 15 feet. * * * In nest-building the female seems to do all the work, her mate sometimes accompanying her on trips to and from the tree, but more frequently flitting about the tops of adjacent trees, occasionally uttering his little warble. One pair I watcht had a nest in a Texas Woodpecker hole in a palo verde tree about 15 feet from the ground. The female brought material to the nest three times in two minutes, then a seven minute interval, followed by two trips in three minutes. The male accompanied her on two trips then made himself scarce. He indulged in no singing and both birds were silent, tho in many cases one or both gave the call note at intervals. Others have mentioned nests of Lucy's warblers in verdins' nests, probably all old winter nests of the male verdin, relined to suit the warbler. O. W. Howard (1899) records such a nest and adds: "Other nests were placed in crevices along river banks where roots of trees were sticking out and one or two were found in natural cavities of the Giant Cactus, or in woodpecker holes therein." We found a nest with young in a cavity in the bleached skeleton of a fallen giant cactus, where I set up my camera and took several photographs of the bird feeding the young. A very pretty nest of this warbler is in the Thayer collection in Cambridge; it was evidently built in the fork of a mesquite limb, supported by a cluster of old and fresh, green twigs; it is made externally of the leaves, petioles, fine green twigs, and flower clusters of the mesquite and is decorated with a few feathers of the white-winged dove; it is lined internally with fine fibers, white cows' hair and black horsehair, and more dove feathers; it measures 4 by 3 inches in outside diameter and 2 by 1-1/3 inside; the outside height is nearly 3 inches, and the inside cup is about 1-3/4 inches deep. A set in my collection was taken from a hole 3 feet above the base of a sandy bank along a wash near the San Pedro River, in Arizona.