In such situations the nest is built in an upright fork or crotch of a bush or sapling, seldom over 6 or 8 feet from the ground or less than 3. Nests are sometimes built at higher levels in apple trees in orchards or in small trees about houses but rarely as high as 30 or 40 feet. Near human habitations, clumps of lilac bushes, often close to windows or doors, are decided favorites, while various kinds of ornamental shrubs about our gardens or grounds also provide suitable nesting sites.
Mr. Du Bois has sent me the data for 30 nests of the eastern yellow warbler found in Minnesota, Illinois, and New York. Among these, 4 were in willows, 3 each in lilacs and alders, 2 each in elms and boxelder saplings, and 1 each in a grapevine, an ash sapling, a spirea bush, and a currant bush. One of these latter, in an unspecified bush, was 14 feet from the ground, and another, in a wild grapevine climbing on a tree beside a coalbin, was 8 feet from the ground; those in the elms were 12 and 14 feet, respectively, from the ground. The remainder were mostly 5 feet or less above ground, the lowest being at a height of 2 feet, in a currant bush near a vegetable garden. He tells of a nest that was built in a wild rose bush at the edge of a small run near his vegetable garden; “this nest was so compactly fabricated as to hold water for some time; I saw about one-fourth inch of water standing in the bottom of it after a heavy rain.”
On two occasions, he has found the new nest to have been built on top of the old nest of the previous year.
F. G. Schrantz (1943) has published the results of a careful study of 41 nests of the eastern yellow warbler in Iowa, during 1938 and 1939, on the restricted grounds of the Iowa Lakeside Laboratory. Among those at heights from 11⁄2 to 5 feet from the ground were 27 in wolfberry bushes (Symphoricarpos occidentalis), 8 in young saplings of boxelder (Acer negundo), 2 in wild gooseberry (Ribes gracile), 1 in wild currant (Ribes floridum), and 1 in an introduced species of honeysuckle. One nest was in a cottonwood at a height of about 10 feet, and another in a boxelder about 15 feet above ground.
Dr. Roberts (1936) says that in the prairie regions of Minnesota, where underbrush is scarce, the yellow warblers build their nests in the cottonwoods in the tree-claims, “against the trunks of the large trees, supporting them on small lateral branches and twigs. * * * These arboreal nests are often fifteen to twenty-five feet from the ground and occasionally still higher.” And in the huge cottonwood trees along the river, he has seen nests placed at elevations of 40 to 60 feet. Others have also recorded nests at heights of 40 and 60 feet.
In Dr. Kendeigh’s (1941) prairie community, “twenty out of twenty-nine nests were placed in buckbrush, with the rest in boxelder, lilac, willow, or currant. The buckbrush is a low bush usually three or four feet high, growing in rather dense thickets in the open, especially in grassy areas of Poa and Agropyron. Nests placed here varied between two and three feet above the ground. The nest found closest to the ground (18 inches) was, however, in a small boxelder. In taller shrubs and trees, the nests were found up to about seven feet above the ground.”
Mr. Schrantz (1943) watched the building of a nest from the first stages of construction to its completion and the laying of the first egg, covering a period of 4 days.
Construction was first observed at 7:45 a. m., on June 12, 1939, when a female Yellow Warbler was seen carrying a tuft of plant-down into a small boxelder sapling. Upon examination, a mass of plant-down about one and one-half inches in diameter was found at a measured height of two feet three inches from the ground in the fork of the sapling. During an hour of observation the female continued to carry plant-down at intervals of about four minutes although once it did not bring any material for twenty minutes. At noon the plant-down mass had increased to about three inches in diameter and was more compactly pushed into the fork. By 6:45 p.m., there were many strands of plant fibers and grasses woven around and through the plant-down in such a way as to wrap and bind the plant-down around the small twigs of the fork. The nest was just assuming a cup-shaped structure. The female was now bringing large loads of a mixture of grasses and plant fibers and working at a rate of about one trip every four minutes. The first day’s building was completed at 7:55 p.m. The nest was now partially surrounded with woven plant fibers and grasses with a slight formation of a rim.
On the second day the work continued and the “rim consisted of plant fibers and grasses woven partly into the original down but mostly into the sides and around the top. At 6:45 p.m., the nest appeared completed with a well-formed cup, plant-fiber and grass rim, and a plant-down floor.” The third day was partly rainy and little was accomplished but “by 8:00 on the fourth morning, the plant-down inside the nest was smoothed out and contained a few strands of fine grasses. * * * During all the observations on the building of this nest the male at no time was seen to bring any nest material. However, since there were many hours during the day when no observations were made, it is possible that he might have helped at some time. * * * At 6:30 a.m., the following day, one egg was found in the nest. * * * The dates of the beginning of construction and the dates the first eggs were laid were obtained for two other nests, and the time which elapsed in both cases was four days.”
Only the female was seen to take part in the building of the nest that Mr. Smith (1943) watched, but my experience was somewhat different. On May 10, 1942, I found a pair of yellow warblers building a nest in the top crotch of a blueberry bush, close to the side of a country road. They were very tame and gave me an unusual opportunity to watch them for over an hour at short range. I parked my car within 5 feet of the nest and took motion and still pictures, with cameras even nearer. The nest was nearly done and they were putting in the lining. Both birds helped in the work, but the female did nine-tenths of it. She came at frequent but rather irregular intervals, bringing a billful of soft plant down that looked like the down from ferns, some of which I found growing nearby, and to which I saw her making frequent trips; the fronds of the cinnamon ferns were just unfolding. This material she deposited in the cup of the nest and settled her body down into it, smoothing the lining into place by turning her body around in different directions, pressing it down with her body and up against the sides of the cup with a sidewise motion of the wings. Occasionally she reached over the rim of the nest, smoothing it with her neck and tucking in the loose ends with her bill. The bottom and outside of the nest seemed to be about finished; one side of it, opposite the most exposed side, was anchored to a nearby twig with strands of plant fiber. The female seemed utterly fearless; the male was more shy, but his streaked breast was occasionally seen at the nest.