T. E. McMullen has sent me the data for 22 nests, found in the Pocono Mountains, Pa. All of these were built in rhododendrons in woods, two on hillsides, one on the edge of a road, one on the edge of the woods, one near a creek, and three along a creek bank. Most of Mr. Brewster's (1938) Lake Umbagog nests were placed low down in yews (_Taxus canadensis_). Apparently, the favorite nesting sites of the black-throated blue warbler are in the broadleaf evergreens, mountain-laurels and rhododendrons, where these are available; next in popularity come the other evergreens (spruces, firs, and hemlocks) of small size; but nests have been found in many places in deciduous seedlings, saplings and sprouts, mainly maple and beech, or in various other bushes or tangles. Mrs. Harding gave me an account of the building of a nest, which she watched during a period of four days. Most of the work was done by the female, but the male helped shape the nest occasionally. The beginning of the nest and much of the main part of it was made of thin strips of the paperlike bark of the white, or canoe, birch firmly bound in place with great quantities of cobwebs; during the early stages of building the rim was anchored with several strands of cobweb to the surrounding leaves and twigs to secure it while the nest was being shaped; this the bird did by sitting in the nest and turning around in all directions, molding it inside with her feet and breast and pressing her tail down over the edge to smooth the exterior. The male sang in the vicinity and brought some of the material, and once he drove away another male. The nest was finished on the fourth day. This process is described in more detail in Mrs. Harding's (1931) paper, where she notes "there is usually an interim of at least twenty-four hours before the first egg is laid. The female lays the eggs at intervals of twenty-four hours--frequently early in the morning. * * * On the morning of the fourth day when the clutch is complete the female commences incubating." _Eggs._--The black-throated blue warbler lays normally four eggs, three are not a rare complement, but five are seldom found. Richard C. Harlow tells me that in over 200 nests that he has examined he has found only 4 sets of five.