Part 11

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.

"Last November 14 a Tennessee warbler behaved most surprisingly. The grass in the yard had grown very long, and I had it cut with a machette. Late in the afternoon, after the usual rain, a lone Tennessee warbler flew down on the fallen grass and began to hop over it, catching small insects.

"It also entered the uncut grass, about a foot high, and disappeared momentarily amidst it. Twice driven up by passing people, each time it promptly returned to the grass. Its third visit to the cut grass was longest. While I stood quietly watching, it hopped deliberately about, much in the manner of a house wren, and gathered an abundant harvest from the fallen herbage. Once it found a caterpillar about an inch long, which it carefully bruised in its mandibles before swallowing it. The warbler was amazingly bold, and hopped over the grass within a yard of my feet, and allowed me to follow closely as it moved away. Early the following morning, and again at the close of the day, the warbler foraged over the lawn in the same fashion. In the evening, it continued to creep slowly over the mown grass and after all other birds had disappeared into their roosts, and the light was becoming too dim to see it clearly."

_Behavior._--Much of the behavior of the Tennessee warbler has been mentioned above, and there is little more to be said. It is a very close sitter on its nest, when incubating, and has been caught there by throwing a hat or a net over it; but, when flushed, it is rather shy about returning to it, usually making its demonstrations of protest by flitting about at a safe distance and nervously uttering a sharp _chip_.

The Prebles (1908) witnessed a rather remarkable flight behavior at Fort Resolution, Mackenzie:

During the forenoon of June 25, an extremely windy day, we observed a remarkable movement of these warblers. They came from the northward, flying over the point of land on which the fort is built In loose flocks of from 10 to 20 individuals. After passing the point, they either struck out directly across the bay or skirted the shore, in either case having to face a strong southeast wind. Some paused a few moments among the low bushes on the point, but the slightest alarm started them off. The flight lasted over two hours, and, during this time, upward of 300 birds were seen from our camp. Two specimens, a male and a female, were collected. The ovaries of the female contained eggs only slightly developed.

_Voice._--Aretas A. Saunders contributes the following: "The song of the Tennessee warbler is a rapid series of short, loud, unmusical notes. It has been compared to the song of the chipping sparrow, but it varies more in pitch, time, and loudness, and is distinctly in two or three parts. To my ear it is much more like the chippering of a chimney swift.

"In 35 records of this song, the number of notes varies from 9 to 25, the average being 17. Only one song has a true trill in it, that is, notes so rapid that they cannot be counted. Each song is of either two or three parts, each part composed of a series of notes on the same pitch and in uniform rhythm. The parts differ from each other in pitch, time, or loudness. In a number of songs, one of the parts is a repetition of 2-note phrases. Loudness generally increases to the end of the song, but sometimes the reverse is true. Some songs rise in pitch to the end and others fall; my records are about evenly divided in this matter. A typical three part song would be something like

_tit it it it it it it pita pita pita pita pita chit chit chit chit chit_.

"Pitch varies from G´´´ to E´´´´, or four and a half tones. Single songs vary from half a tone to three and a half tones, averaging one and a half. The length of songs varies from 1-4/5 to 3-1/5 seconds. An individual bird may sing a dozen different variations of the song in a short time. On the other hand, I have heard three birds in one tree singing alternately, the songs of all three being exactly alike so far as my ear could determine."

Francis H. Allen gives me his impression of the song as follows: "The song bears some resemblance to that of the Nashville warbler, but is easily distinguished. I have written it

_wi-chip wi-chip wi-chip wi-chip, wi-chip wi-chip chip chip chip chip chip chip chip_.

The higher notes in the middle sometimes appear to be monosyllables, and they are sometimes omitted. The series of _chips_ at the end are very emphatic, and the last one is perhaps accented somewhat. All the notes are staccato."

Various other renderings of the song have appeared in print, but they all give the same impression of a variable, loud, striking song which, once learned, can be easily recognized. The bird is a very persistent singer rivaling the red-eyed vireo in this respect. Bowdish and Philipp (1916) write: "As a basis for estimating the frequency of song repetition, counts were kept on three singing birds for a period of 5 minutes each, with a result of 32, 36, and 22 songs, respectively, within the period. In one instance, a bird was observed to sing while on the wing, repeating the song twice in the course of a short flight." Albert K. Brand (1938) found the pitch of the Tennessee warbler's song to be well above the average, the approximate mean count being 6,600 vibrations per second, the highest note about 9,150 and the lowest 4,025; this compares with an approximate mean of 8,900 vibrations per second for the black-poll warbler, and about 4,000 for the average passerine song.

_Field marks._--The Tennessee warbler has no prominent wing-bars and no very conspicuous field marks. It might be mistaken for one of the small vireos, but its bill is much more slender and acute. The male has a gray crown, a light line over the eye, and a dusky line through it; the upper parts are bright olive-green and the under parts grayish white. The female has a greener crown and more yellowish under parts. For more details, see the descriptions of plumages.

_Fall._--The fall migration starts early in August, but is quite prolonged, many birds lingering in the northern States until early in October and in the southern States all through that month. During some seasons and at certain places the Tennessee warbler is exceedingly abundant, sometimes far outnumbering any other species, but it is very variable in its abundance.

Mr. Trautman (1940) says that at Buckeye Lake, Ohio, "during some years not more than 20 individuals could be recorded in a day in the southward migration, nor more than a 100 in the season. In other years the bird rivaled the Myrtle Warbler in numbers, and as many as 1,000 individuals could be seen in a day and several thousands during a migration. * * * Throughout the southward migration the species did not confine itself to the upper sections of the taller trees as in spring, but was found in almost equal numbers in smaller trees and brushy thickets, in bushes and saplings along fence rows, and in weedy fields."

Professor Cooke (1904) says of the fall migration route: "The principal line of migration is from the Mississippi Valley across the Gulf of Mexico to Mexico and Central America. The eastern part of this route probably extends from the southern end of the Alleghenies across northwestern Florida to the coast of Yucatan and Honduras." A. H. Howell (1932), however, gives several records for central and southern Florida, and says: "In autumn, Weston reports a large migration on October 26 and 27, 1925, when 31 birds were killed at the lighthouse near Pensacola on the two nights, and large numbers seen on the morning of October 26 in vacant lots in the city."

Dickey and van Rossem (1938) say of the migration in El Salvador:

During the fall migration of 1925, Tennessee warblers arrived in the vicinity of Divisadero on October 13. No advance guard, that is, individuals arriving ahead of the main flights, was observed in this case. On the above-mentioned date they were suddenly found to be present in numbers, and from then on were common in every lowland or foothill locality visited. In point of relative abundance this was by far the most common warbler (resident or migratory) throughout the coastal plain and in the foothills, but it was greatly outnumbered by _Dendroica virens_ above 3,000 feet.

The manner of occurrence was usually as small flocks of six or eight or even twenty or more birds. These combined with several other species to make up larger flocks which worked ceaselessly through the crown foliage of low, semi-open woodland. However, many were found even in the tall, dense swamp forests along the coast and also in the oak woods on Mt. Cacaguatique.