Brewster (1878a) mentions a nest taken from a deep cavity that “when removed presents the appearance of a compact mass of moss five or six inches in height by three or four in diameter. When the cavity is shallow, it is often only scantily lined with moss and a few fine roots. The deeper nests are of course the more elaborate ones. One of the finest specimens before me is composed of moss, dry leaves, and cypress twigs. The cavity for the eggs is a neatly rounded, cup-shaped hollow, two inches in diameter by one and a half in depth, smoothly lined with fine roots and a few wing-feathers of some small bird.”
In Dr. Walkinshaw’s (1938) Michigan nests, “moss constituted the bulk of the nesting material in nearly all cases, completely filling the nest space whether it was large or small. On top of this the nest proper was shaped and a rough lining of coarse grape-bark, dead leaves, black rootlets procured from the river-banks, and poison-ivy tendrils was added. Above this a lining of much finer rootlets, leaf-stems, and very fine grasses was used.”
In addition to the materials listed above Meyer and Nevius (1943) mention hackberry leaves, hairs, pine needles, horsehair, and cedar bark in their Tennessee nests. They say that from 6 to 10 days were required for nest construction, and that from 3 to 5 days more elapsed before the first eggs were laid. Their four nests were all in bird-boxes; one was in an orchard over plowed ground, one over a lotus pond in a wooded ravine, and two were over lily pools near buildings.
Dr. Walkinshaw (1938) publishes a map showing the location of 21 nesting boxes along the winding banks of the Battle Creek River, in Calhoun County, Mich., and writes: “Of the 28 nests found during 1937, 19 were in bird-houses over running water, 6 were in stubs over water (2 of which were over running water), and the other 3 were in natural holes back from the river bank. Of 44 nests found from 1930 through 1937, excluding the 21 in bird-houses, six were over running water in old woodpecker holes, one in a bridge-support in a slight depression, and nine in natural holes over standing water. Seven were in old woodpecker holes from two to a hundred and sixty feet back from the river-bank.”
Many and varied are the odd nesting sites occupied by prothonotary warblers. Dr. Thomas S. Roberts (1936) writes:
The vagaries of this bird in choosing artificial nesting-places are shown by the positions of the following nests. On the La Crosse railroad bridge: in a cigar-box nailed on the engine-house on top of the draw; on one of the piers; in a metal ventilator-cap four inches in diameter, that had fallen and lodged just at the point where the draw banged against the pier, and close under the tracks; in a shallow cavity in a piece of slab-wood nailed to a trestle-support close under the road-bed of the railroad; these all far out in the middle of the Mississippi River. Still others are: in a Bluebird box on a low post by a switching-house and busy railroad platform; in a cleft in a pile in the river; in a tin cup in a barn, to reach which the birds entered through a broken pane of glass; in a pasteboard box on a shelf in a little summer-house; in an upright glass fruit jar in a house-boat; and other similar situations. In most cases the birds had to carry the nesting-material long distances, especially to the places on the bridge.
John W. Moyer (1933) relates an interesting story that was told to him by people living in a farm house along the Kankakee River. A pair of these warblers built their nests and raised their broods for three consecutive seasons in the pocket of an old hunting-coat, hung in a garage; each year the man cleaned out the nest and used the coat in the fall, and the next spring the birds used it again. M. G. Vaiden tells me of a similar case.
Nests have been found in buildings, on beams and other supports. Louis W. Campbell (1930) reports two on shelves in sheds, one in a small paper sack partly filled with staples and another in a coffee can similarly filled. Nests in cans in various situations have been found a number of times, and others have been reported in a tin pail hung under a porch, in a mail box, in a box on a moving ferry boat, in a Chinese lantern on a pavilion, and in an old hornets’ nest.
Dr. Walkinshaw writes to me: “At Reelfoot Lake, Tenn., during July, 1940, I found 8 nests of the prothonotary warbler, all built a few feet above the water in small natural holes in cypress knees. Evidently these are regular late-summer nesting sites.” The knees were farther under water earlier in the season. Most of his 76 Michigan nests were over water, or less than 100 feet from it; but 10 were 300 or more feet away from it and 2 were over 400 feet away. M. G. Vaiden tells me of a pair that nested in the tool box of a log-loading machine that was in daily operation, hauling logs.
Eggs.—From 3 to 8 eggs have been found in nests of the prothonotary warbler, from 4 to 6 seem to be the commonest numbers, 7 is a fairly common number, and at least 3 sets of 8 have been reported; in the J. P. Norris series of 70 sets are 34 sets of 6, 15 sets of 7, and 2 sets of 8.