Part 22

Nesting.--Prior to the beginning of the present century very little authentic information on the nesting habits of the Tennessee warbler was available. Professor Cooke (1904) records two sets of eggs taken by one of the parties of the Biological Survey in 1901 at Fort Smith, Mackenzie, of which he says: "These eggs are among the first absolutely authentic specimens known to science." And Dr. Chapman (1907) remarked: "The Tennessee Warbler awaits a biographer." Since then, we have learned much about it, mainly through the writings of B. S. Bowdish and P. B. Philipp, who found it breeding abundantly in New Brunswick. In their first paper (1916) they describe the summer haunts and the nesting habits of this warbler as follows:

The region in question is particularly well adapted to the nesting requirements of the Tennessee Warbler, as we noted them during the above period. Extensive lumbering has removed the greater part of the large growth spruce and balsam timber, which forms the great bulk of the forests of this region, leaving areas of small trees, which, in the older clearings, have grown thickly, and to an average height of ten feet. These are interspersed with areas of more or less open, large timber, and others where the second growth has reached little more than the proportions of somewhat scattered shrubbery. The essentially level surface is frequently scored by slight depressions which form the beds of tiny streams, bordered on either side by boggy ground, dotted with grass tussocks, bushes and small trees, and overspread with a luxuriant growth of moss. Such areas are most numerous in cleared tracts, but not infrequent in the edges and the more open portions of the woods. These are the summer home-sites of the Tennessee Warbler. * * *

At the time of our visit to the breeding country, in the middle of June, nest building was completed and full sets of eggs had been laid. Altogether, ten nests were located, all built on the ground in substantially the same general sort of situation, and all but two were found by flushing the bird. The nest is built in the moss, usually in a wet place at the foot of a small bush, and in most cases in woods, somewhat back from the more open part of the clearings. A hollow is dug in the moss, usually beneath an overhanging bunch of grass. The nest is in nearly every case entirely concealed and it is impossible to see it from any view-point without displacing the overhanging grass. Consequently unless the bird is flushed it would be all but impossible to find it. The outer foundation of the nest is of dry grass forming quite a substantial structure. Several nests had wisps of grass stems extending from the front rim, as noted in description of the first nest below. It is lined, usually, with fine dry grass, to which in some instances the quill-like hairs of the porcupine, or white moose hairs, are added, and more rarely still, fine hair-like roots which were not identified. * * *

This species seems to be somewhat gregarious. In 1914, in one small clearing, five males were heard singing at the same time. In 1915, in the same clearing, three males were heard singing at once, and two nests were found. In almost every clearing of suitable size at least two pairs of birds were found, the nests being sometimes located rather close together. * * *

On the second day of our sojourn, June 19, we visited one of the typical nesting places of this warbler, a boggy cleared swale, with scattering, small second growth, and soon flushed a female from a nest containing six fresh, or practically fresh, eggs. This nest, typical of the majority of those found in both construction and situation, was placed in the side of a small tussock, bedded in moss and completely overhung by the dead grass of the previous year's growth. The nest was composed entirely of fine, nearly white, dead grass stems. From the front rim protruded outward and downward, a wisp of dead grass tips, lying over the lower grasses in the tussock, and shingled over by the overhanging grass, establishing a continuity of the side of the tussock, thus cunningly adding to the perfect concealment. A tiny tree and one or two bush shoots grew from the tussock, close to the nest and this feature was typical of the greater number of the nests found.

They give the measurements of four nests; the outside diameter varied from 3 to 4 inches, the inside diameter from 1-1/8 to 2 inches, the outside depth from 2 to 3-1/4, and the inside depth from 1-1/8 to 1-1/2 inches. What nests I have seen, in collections, all appeared much flatter than the above measurements indicate, but they were probably flattened in transit. All that I have seen seemed to consist entirely of very light, straw-colored grass rather lightly arranged. Some observers mention moss in the composition of the nest, but the nests are evidently made in the moss and not of it.

Dr. Paul Harrington mentions in his contributed notes four nests that he found near Sudbury, Ontario: "The nests were all similarly situated in a clump or mound of sphagnum, well arched so that to obtain a full view of the nest it was necessary to part the sphagnum, in shaded areas on the borders of black spruce bogs. These, and others I have examined, have always been constructed entirely of fine straw-colored grasses, whereas in those of the Nashville warbler a few hairs or gold-threads were generally incorporated in the structure."

Philipp and Bowdish (1919) record in a later paper the finding of a number of additional nests in New Brunswick, and say: "The experience of the past two years has demonstrated that while the boggy ground nesting, previously described, is the really typical and by far the most common form, not a few of these birds nest on higher and dryer ground. One such nest, found June 24, 1918, was well up on a steep hillside, in rather open woods, on fairly dry ground, utterly devoid of moss and grass cover. It was built among a thick growth of dwarf dogwood, and under a tiny, crooked stemmed maple sapling, very well concealed, and was rather more substantially built than the average nest of this species."

The nesting history of the Tennessee warbler would not be complete without mentioning two authentic records made in 1901. J. Parker Norris, Jr. (1902), reported receipt of a set of four eggs, collected by Major Allan Brooks on June 15, 1901, at Carpenter Mountain, Cariboo, British Columbia. This is apparently the first authentic set of eggs ever taken, as those mentioned above by Professor Cooke were taken a few days later. In this far western locality, the birds "generally frequented the clumps of aspen trees and Norway pines, where the ground was covered with a thick growth of dry pine grass." Major Brooks found several other nests in the same locality, and says in his notes: "The nests were always on the ground, sometimes at the foot of a small service berry bush or twig. They were all arched over by the dry pine grass of the preceding year, this year's growth having just well commenced."

The Fort Smith nests, referred to by Professor Cooke, were recorded by Edward A. Preble (1908) as follows:

Nests containing eggs were found by Alfred B. Preble on June 20 and 27, the eggs, five in number, being fresh in each instance. The first nest was embedded in the moss at the foot of a clump of dead willows near the edge of a dense spruce forest. It was rather slightly built of dead grass with a lining of the same material, and was protected from above by the overhanging bases of the willows, and by the strips of bark which had fallen from them, so that the nest could be seen only from the side. The second nest was more bulky, was composed outwardly of shreds of bark, coarse grass, and Equisetum stems, and was lined with fine grass. It was placed on the ground beneath a small fallen tree, in a clearing which had been swept by fire a year or two previously.

W. J. Brown, of Westmount, Quebec, tells me that he and L. M. Terrill in an hour found 16 nests of this warbler in a corner of a sphagnum bog, and, "there must have been about 100 pairs nesting in this ideal spot at the time."

Eggs.--The Tennessee warbler lays large sets of eggs, from four to seven, with sets of six common. Philipp and Bowdish (1919) state, "it appears that more full layings of six eggs are to be found than of five."

The eggs are ovate to short ovate and have only a slight luster. The ground color is white or creamy white, and the markings, in the form of speckles and small spots, are in shades of "chestnut" and "auburn," sometimes intermingled with "light vinaceous-drab." On some the markings are well scattered over the entire surface while on others they are concentrated at the large end, often forming a loose wreath. Only occasionally do the spots assume the proportions of blotches. The measurements of 50 eggs average 16.1 by 12.4 millimeters; the eggs showing the four extremes measure =17.8= by 12.7, 16.8 by =13.1=, =14.8= by 12.3, and 15.8 by =11.4= millimeters (Harris).

Young.--Nothing seems to have been recorded on the period of incubation, which is performed by the female alone. Nor do we know anything about the care of the young or their development.

Plumages.--Dr. Dwight (1900) says that the young Tennessee warbler in juvenal plumage, in which the sexes are alike, is similar to the young Nashville warbler in similar plumage but lacks the brownish cast and has a faint transocular stripe. He describes it as "above dull grayish olive-green, the rump brighter. Wings and tail clove-brown, the primaries whitish edged, the secondaries, tertiaries and wing coverts greenish edged with two yellowish white wing bands. Below grayish buff rapidly fading when older to a greenish gray; abdomen and crissum pale straw-yellow. Trace of ducky transocular streak."

The incomplete postjuvenal molt, involving the contour plumage and the wing coverts, but not the rest of the wings or the tail, begins about the middle of July. This produces the first winter plumage, in which the young male is "above, bright olive-green, gray tinged on the pileum. Below, olive-yellow darker on the flanks, the abdomen and crissum white. Superciliary line and orbital ring buff. Transocular streak dull black." The young female "differs from the male in having the lower parts more washed with olive-green." Young and old birds are now practically indistinguishable.

Dickey and van Rossem (1938) say that the prenuptial molt "begins in late February and is not finished before about the middle of March. The molt involves most of the anterior body plumage, but progresses so slowly that this species never has the ragged 'pin-feathered' appearance so often seen in Dendroica aestiva at the spring molt." Dr. Dwight noticed the beginning of this molt as early as January 14. He says it "involves chiefly the head, chin and throat. The ashy gray cap is acquired, the chin, throat, and superciliary line become white, the throat is tinged with cream-buff and the transocular streak black. The yellow tints of the feathers retained below are lost by wear." In the female, this molt is less extensive than in the male, and "the crown never becomes, even in later plumages, as gray as that of the male, but always has a brown or greenish tinge."

Subsequent molts consist of a complete postnuptial in July and a partial prenuptial molt in late winter and early spring as in the young bird.

Food.--Bowdish and Philipp (1916) sent four stomachs of birds collected in June to the U. S. Biological Survey for analysis. One of these was empty. Of the other three, one contained 8 small caterpillars (Tortricidae), 35 percent; dipterous fragments, 23 percent; a small spider, 2 percent; and scalelike fragments (perhaps of some catkin), 40 percent. Another held a camponotid ant, 16 percent; at least 78 small caterpillars (Tortricidae), 75 percent; a snail (Vitrea hammoides), 4 percent; and unidentified vegetable fragments, 5 percent. The other contained 3 lampyrids (near Podabrus), 8 percent; a small coleopterous (?) larva, 3 percent; about 15 small caterpillars (as above), 25 percent; a neuropterous insect (apparently a caddis fly), 50 percent; 2 small spiders, 14 percent; and a trace of unidentified vegetable matter.

Several observers have complained that Tennessee warblers do considerable damage to grapes, and this is undoubtedly true. W. L. McAtee (1904), while investigating the damage done by this and the Cape May warbler, found that--

in the arbor under observation, which was a small one, scarcely a grape and not a cluster was missed. The damage, however, was inconsiderable as the birds did not commence to use their appropriated share of the crop until the owner had taken all he desired. * * * Both species were constantly busy catching insects on the vines, and on a walnut and some appletrees near by. Frequently, however, they dashed into the vines and thrust their bills quickly into a grape. Sometimes they withdrew them quickly; again they poked around in the interior of the grape a little, and always after these attacks, they lifted their heads as in drinking. This action suggested a reason for piercing the grapes, that I am satisfied is the true one, that is, the obtaining of liquid refreshment.

A supply of available drinking water for the birds, might help to protect the grapes. And, as the warblers feed on insects that seriously damage the grapevines, the good work they do may compensate for the grapes that they damage. The stomach of one Tennessee warbler examined by Mr. McAtee contained a Typhlocyba comes, an especial pest of the grape, a destructive jassid or leafhopper, 6 caterpillars which were doing all in their power to eat up the leaves remaining on the vines, 2 spiders, a bug (Corizus), a weevil, and one parasitic hymenopteron (the only insect that was not harmful).

S. A. Forbes (1883) found that a stomach taken from an orchard infested by canker-worms contained about 80 percent of these destructive larvae and about 20 per cent beetles. Professor Aughey (1878) observed these warblers catching young locusts in Nebraska. Clarence F. Smith adds, in some notes sent to me, that "in the fall, during migration time, Tennessee warblers often glean their food from dense patches of such weeds as sunflower, goldenrod, and ragweed," and that "sumac, poison ivy, and other berries are sometimes eaten in small quantity."

F. H. King (1883) has considerable to say about the damage done to Delaware and Catawba grapes in Wisconsin; as soon as they are wounded, they are attacked by ants, bees, and flies and soon destroyed. But he thinks the service rendered more than compensates for the harm done. He refers to the feeding habits of the Tennessee warbler as follows:

It is very dexterous in its movements, and obtains the greater part of its food upon and among the terminal foliage of trees. Titmouse-like, it often swings pendant from a leaf while it secures an insect which it has discovered. Small insects of various kinds, not especially attractive to larger birds, are destroyed by this species in large numbers; and its slender, acute bill serves it much better in picking up these forms than a heavier, more clumsy one could. * * * Of thirty-three specimens examined, two had eaten two very small hymenoptera (probably parasitic); seven, thirteen caterpillars; three, fifteen diptera; six, thirteen beetles; three, forty-two plant-lice, among which were two specimens of the corn plant-louse Aphis maidis (?); three, thirty-five small heteroptera, .09 of an inch long; and one, eleven insect eggs.

Alexander F. Skutch has sent me the following interesting notes on the feeding habits of the Tennessee warbler in Central America: "I was surprised to find last month [March] that these warblers were visiting my feeding shelf on the guava tree in the yard. About the only food I ever serve to the birds on this table is bananas and occasionally plantains; and my chief guests are tanagers of about half a dozen brilliant kinds, a few finches, honeycreepers, and wintering Baltimore orioles. But the Tennessee warblers soon formed the habit of visiting the table and sharing the food with the bigger resident birds.

"Some seemed to linger in the vicinity much of the day, making frequent visits to the board and each time eating liberal portions of banana or the somewhat harder ripe plantain. They were intolerant of each other, and one individual would not let a second alight on the board until it had finished its own meal, although there was plenty of room and plenty of food for all. I have noticed also that the Tennessee warblers chase each other as they forage among the trees in wintering flocks. I cannot recall ever having seen any other wood warbler eat banana.