Part 37

In western Pennsylvania, "its local breeding range is correlated rather closely with the distribution of the white pine and the hemlock. Where these conifers prevail, the Black-throated Green appears, although in the mountains it is by no means averse to hardwood timber, if high and dense" (Todd, 1940). And, in the Pymatuning Swamp region, "wherever tall black birches and equally tall, slender hemlocks grew side by side, the Black-throated Green Warblers were almost sure to be found, and no less than twenty pairs were located" (Sutton, 1928). Referring to the central Allegheny Mountain region, Prof. Maurice Brooks (1940) says that "this species, in its distribution within our area, presents one of the most puzzling problems with which we have to deal. It occurs everywhere at high elevations, in spruce, hemlock, northern hardwoods, white pine, oak-pine scrub, and oak-hickory."

Still farther south, on Mount Mitchell, in western North Carolina, Thomas D. Burleigh (1941) found it to be "a plentiful breeding bird in the thick fir and spruce woods at the top of the mountain, appearing in April when the ground is frequently still covered with snow and lingering in the fall until early October."

_Spring._--From its winter home in Mexico and Central America, the black-throated green warbler, starting early in March, migrates northward through eastern Texas and up the Mississippi Valley, mainly in the forested areas. I noted it in the great wave of warblers migrating along the Texas coastal islands early in May. The fact that it is so rare in southern Florida, and still rarer in Cuba, suggests that many individuals must make the perilous flight from Yucatan across the Gulf of Mexico to the Gulf States. From Louisiana it takes a more northeasterly route, mainly along the Alleghenies, to New England and beyond. It is one of the earlier warblers to arrive in Massachusetts, often during the last week in April. The birds come along in waves, the first wave consisting mainly of males and later waves containing the females in larger numbers. The passage of individuals seems to be fairly rapid, but the species may be present for nearly a month at any point along its migration route. While migrating it may be seen, like other warblers, almost anywhere--in the tops of woodland trees, in roadside trees and shrubbery, in gardens and in parks, before it settles down in its favorite breeding haunts. There must be a very heavy migration through Ohio, for Milton B. Trautman (1940) says that in the "larger flight 50 to 125 were daily recorded, and it was evident that there were several thousands present."

_Nesting._--Although the black-throated green warbler is one of our commonest breeding warblers, I have never found its nest in my home territory, though I have spent many hours hunting for it in its favorite pine woods. While hunting through a somewhat open tract of pitch pines on Martha's Vineyard, Mass., on June 8, 1919, with Frank C. Willard, we found a nest with four fresh eggs 8 feet from the ground in a small pine; it was saddled on an upward-slanting limb and partially supported by a whorl of three small branches. It was a pretty nest, made of grasses, seaweed, and strips of inner bark, and was lined with fine grasses, cowhair, horsehair, and a few white feathers. The male was incubating and was very tame, coming within a few feet of us; he also returned and sat on the empty nest after Mr. Willard had removed the eggs.

On June 4, 1910, Herbert K. Job showed me a nest near New Haven, Conn., in mixed deciduous woods; it was about 11 feet from the ground, built against the trunk of a large chestnut sprout and supported by a small dead branch and two live twigs; the leaves on this twig screened the nest from above, one leaf forming a complete canopy over the nest, the tip of it being tucked into the rim. It was made largely of materials similar to those in the one previously described, there being three large feathers on the rim and many small feathers in the lining.

The only other nest I have ever seen was found on the island of Grand Manan, New Brunswick, on June 11, 1891; it was placed only 3 feet from the ground between two horizontal branches and against the trunk of a small spruce beside a cowpath in coniferous woods. It was a compact, deeply hollowed, structure made of fine twigs, mosses, birch bark, strips of inner bark, and weed stems, and it was lined with white cowhair and a few feathers.

There is a set in my collection, given to me by Fred H. Carpenter, said to have been taken from a nest only 8 inches from the ground in a small red cedar in an old neglected pasture in Rehoboth, Mass. The nest, now before me, seems to be typical of the species.

The nests mentioned in some notes sent to me by Miss Cordelia J. Stanwood, of Ellsworth, Maine, were in spruces or hemlocks at low or moderate heights, but Knight (1908) says that "near Bangor the species builds fifty to seventy feet up in the larger, taller pine trees." Robie W. Tufts tells me that, of some 20 or 30 nests that he has seen in Nova Scotia, "all have been built in conifers, including hemlock, spruce, and pine." In New York and Pennsylvania, hemlocks seem to be the favorite nesting trees, but nests are sometimes placed in beeches or yellow birches; the nests in hemlocks are usually placed on horizontal branches at a considerable height from the ground and generally well hidden in the foliage. A nest examined by Dr. George M. Sutton (1928) at Pymatuning Swamp "was saddled on a horizontal bough only about twenty-five feet from the ground, in a comparatively small hemlock. The nest was very deep and beautifully constructed, its lining including bits of hair, fur, and soft feathers, and its foundational material consisting chiefly of slender and uniform twigs of dead hemlock."

The two nests studied by F. A. Pitelka (1940), in northern lower Michigan, were on horizontal branches of Norway pines (_Pinus resinosa_), 23 and 12 feet from the ground, respectively. The materials used in the nests were largely similar to those mentioned above, with the addition of woollike plant fibers and short pine twigs in the lining, and with "a considerable quantity of hypnaceous mosses and bits of birch bark" used as trimmings.

Dr. Paul Harrington writes to me: "I have found this bird nesting in pure deciduous forests on two occasions." One nest was 40 feet up in the crotch of an ironwood, and the other was 20 feet from the ground in a small elm, both in Ontario. Edward R. Ford has sent me the following note: "On Gull Island, about ten acres in extent, which lies in northwestern Lake Michigan, we found the black-throated green warbler in an unusual nesting niche. About half of the island's area is northern hardwood forest, whose floor cover is largely of American yew (_Taxus canadensis_). At a height of but two or three feet, among the sprays of this ground-hemlock, we discovered two nests of the species named. Each of these, July 12, 1918, held four eggs. There was a third nest, empty but evidently used that season."

Nests have also been found in maples, in white, gray, and black birches, in alders and probably in other deciduous trees and bushes. And the following unusual nesting sites are of interest: William Brewster (1906) mentions a nest that he found "in a barberry bush growing in an open pasture at Arlington Heights, one hundred yards or more from the nearest woods." He also has a nest, taken by C. H. Watrous in Connecticut, that was on the ground "among a large clump of ferns in a very low and damp place under a heavy growth of hemlocks" (Brewster, 1895). John C. Brown (1889), of Portland, Maine, mentions a nest that was built in a grapevine growing luxuriantly about a pagoda at some distance from any woods; it was well hidden from the outside by the foliage, but in plain sight from inside the pagoda. And B. S. Bowdish (1906) records a New Jersey nest that "was built between the stems of a 'skunk cabbage' plant, and fastened to a catbriar and the twigs of a dead bush, and was about fourteen inches from the ground, in a very wet part of the swamp."

Miss Stanwood (1910) watched a pair of black-throated green warblers building a nest in a fir tree, of which she writes:

First they laid knots of spider's silk and little curls of white birch bark in the shape of the nest, on the horizontal fork about midway of a branch six feet long. Next bits of fine grass, a little usnea moss, and cedar bark fibre. Both the male and female worked on the nest, until observed, the female shaping it with the breast each time they added a bit of material. Around the top were carefully laid the finest gray spruce twigs. These were bound together with masses of white spider's silk. The white curls of birch bark, the much weathered twigs, the fluffy shining bands and knots of spider's silk, made a very dainty looking structure. After the first morning, I did not see the male about the nest. As a general thing, I find that, if birds are observed building, the male usually leaves his part of the work to the female. The lady bird continued to shape the nest with her breast, turning around and around, as if swinging on a central pivot, just her beak and tail showing above the rim. If I came too near, she stood up in the nest as if to fly. If I withdrew to a respectful distance, say three yards, she went on with her work of shaping the nest. On the second day the rim of the nest seemed about completed. It was narrower than the rest of the cup and beautifully turned. Nothing to speak of had been done to the bottom. On the fourth day, by touching the inside of the nest with the tips of my fingers, I judged that the lining was about finished. It consisted of rabbit-hair and horse-hair, felted or woven together so as to be very thick and firm. Between the foundation of twigs and bark and the hair lining was a layer of fine hay of which the mouth of the nest was chiefly shaped. I never saw a more substantial looking little nest. It was also one of the most beautiful I have ever found, a perfect harmony in grays.

A very pretty nest in my collection is largely made, externally, of usnea and is profusely decorated with masses of the curly outer bark of the yellow birch. The larger of two nests before me measures about 4 by 3-1/2 inches in outer diameter, the smaller about 3 inches; both are about 2 inches high, nearly 2 inches wide and 1-1/2 deep inside.

_Eggs._--The black-throated green warbler usually lays 4 eggs to a set, but quite often 5. These are ovate to short ovate and slightly glossy. The ground color is grayish white or creamy white. The markings consist of specks, spots, blotches, or small scrawls of reddish browns, such as "auburn," "chestnut," "bay," "Mars brown," or "russet," with underlying spots of "light brownish drab," "deep brownish drab," or "light purplish drab." Generally the markings are concentrated at the larger end, where they usually form a wreath, but occasionally the spots are well scattered over the entire egg. There is considerable variation. Some eggs have a faint wreath of the pale drab coloring which is relieved with a few bold spots or scrawls of dark "bay" or "Mars brown." Others are richly spotted and blotched equally with browns and drabs, or they may have a solid ring of "russet" blotches which completely covers and conceals the drab undertones. The measurements of 50 eggs average 17.0 by 12.7 millimeters; the eggs showing the four extremes measure =18.8= by 12.8, 17.2, by =13.4=, =15.5= by 12.2, and 18.0 by =12.0= millimeters (Harris).

_Young._--It is generally conceded that the period of incubation is about 12 days and that the young remain in the nest from 8 to 10 days, depending on the amount of disturbance. Probably the female does most, or all, of the incubating and brooding, but both sexes assist in feeding the young and in swallowing or removing the fecal sacs. Miss Stanwood (1910b) refers to the development of the young as follows: "On the third day the young birds grow rapidly, burnt-orange in color, covered with an abundant supply of burnt-umber down. The quills and pin feathers showed blue-gray through the skin, and the eyes were just beginning to open." At another nest, "on the eighth day, the nest was simply stuffed full of little green-gray birds, strikingly like the color of the nest.

* * * On the eleventh day, quite early in the morning, as I neared the nesting place, I heard the fledglings calling from the tree-tops. Soon I caught a glimpse of the Black-throated Green Warblers marshalling their little band away."

Margaret M. and L. B. Nice (1932) made detailed studies of two nests of this warbler, to which the reader is referred. I quote from their summary:

1. The young in the first nest were raised with no assistance from the male until the last two days, when he brought 11 meals in contrast to his mate's total of more than 245. The young in the second nest were raised entirely by the female. 2. The first female incubated for periods ranging from 34 to 50 minutes, absenting herself for periods ranging from 9 to 26 minutes. The second female once incubated for 99 minutes at a stretch; her absences varied from 13 to 20 minutes. 3. Both females brooded for longer periods than the majority of arboreal Warblers that have been studied, averaging 15.1 and 18.3 minutes respectively. 4. Both females fed at slow rates, the average for the first being once in 19.7 minutes, for the second once in 16.3 minutes. * * * (6). Both females made definite efforts to get their last young out of the nest and to lead them to a distance.

Pitelka (1940b) gives many interesting details on the home life of the black-throated green warbler, illustrated with charts and tables that are not suitable for inclusion here, but his paper is well worth careful study.

Reading and Hayes (1933) made some intimate studies of these warblers at their nest; referring to the food of the young, they say: "Observations at less than two feet revealed the tremendous value of these birds as insect destroyers. Spiders, may-flies, green caterpillars (Anisota), ants, small noctuid moths, ichneumon flies, crane flies, and many smaller diptera made up the whole of their menu. While the few spiders and ichneumon flies were harmless or possibly beneficial, many of the other insects were injurious."

_Plumages._--Dr. Dwight (1900) calls the natal down sepia-brown and describes the juvenal plumage, in which the sexes are alike, as "above, sepia-brown or drab. Wings and tail dull black, edged with ashy or olive-gray; two wing bands white; the outer three rectrices largely white. Below, dull white, dusky on the throat, spotted on the breast and sides with dull olive-brown. Indistinct grayish white superciliary line. Dusky transocular streak."

A partial postjuvenal molt, beginning in July and involving the contour plumage and the wing coverts but not the rest of the wings or the tail, produces the first winter plumage, in which the sexes are distinguishable. He describes the young male as--

above, greenish olive-yellow, the upper tail coverts ashy or plumbeous gray edged with olive yellow. The feathers of the crown and back especially have concealed black shaft streaks. The wing coverts are black, edged with olive green; two broad white wing bands tipped faintly with yellow. Below, faint primrose-yellow, white on the crissum; the breast and a spot on the flanks canary, the chin, sides of head and neck and superciliary line bright lemon-yellow; a variable area on the throat seldom including the chin, black, veiled by long narrow edgings, the sides and flanks broadly streaked and similarly veiled. Transocular and rictal streaks dusky; lores grayish. * * * In first winter plumage the female is browner than the male, without the black throat and the side streaks obscure; some specimens with much black may, however, easily be mistaken for dull first winter males.

The first nuptial plumage is acquired by a partial prenuptial molt, "which involves chiefly the head, chin and throat and not the rest of the plumage. The black chin is assumed by the male and the forehead becomes yellower by moult, wear removing the edgings everywhere so that the streakings below and the throat become jet-black. Young and old become practically indistinguishable, except that the wings and tail of the young bird will average browner and more worn with the edgings duller." In the female, "the first nuptial plumage differs very little from the first winter, wear bringing out the streaking, while a few feathers are assumed by moult on the chin."

A complete postnuptial molt occurs in July, producing the adult winter plumage, in which the male "differs somewhat from the first winter, the black of the throat extending uninterruptedly to the apex of the chin, further down on the throat, and in broader stripes on the sides; the wings and tail are blacker and the edgings grayer, especially on the tertiaries; the concealed black of the back more extensive. The veiling is conspicuous on the throat." The adult winter female is much like the first winter male, "and may have considerable black on the throat, and even the chin."

The adult nuptial plumage is acquired mainly by wear, with only slight indications of molt, as in the young bird. Dr. Dwight says of the female: "The adult nuptial plumage is, in extreme examples, hardly distinguishable from the male, but usually the black is much restricted and the chin yellow, merely spotted with black."

_Food._--We have only scattering reports on the food of the black-throated green warbler. S. A. Forbes (1883) examined the stomach of one taken in an orchard infested with canker-worms in Illinois, and found it to contain 70 percent of these destructive caterpillars, 15 percent beetles, 5 percent Hemiptera, and the remaining 10 percent Hymenoptera, gnats, coleopterous larvae and mites. Five stomachs of Nebraska birds, collected by Professor Aughey (1878), contained an average of 23 locusts and 21 other insects. Of twelve specimens examined by F. H. King (1883) in Wisconsin, "one had eaten a moth; three, seven caterpillars; one, two diptera; one, six larvae--probably caterpillars; three, eleven beetles; and one, a heteroptera."

Knight (1908) from Maine writes: "The food consists almost entirely of insects, including beetles, flies, moths, spiders, grubs, larvae and in general the sorts of insects found on the limbs and foliage of the various evergreen trees and especially on the pines. Only rarely do they take their prey in the air, preferring to diligently seek it out among the branches and foliage."

Probably all the items mentioned in the food of the young are also eaten by the adults. Forbush (1929) adds to the list leaf rollers, leaf-eating caterpillars of various kinds, and plant-lice. Evidently these warblers are among the best protectors of our forest trees. W. B. Barrows (1912) says that they are "particularly fond of the berries of the poison-ivy, and to a less extent of those of the junipers." J. K. Terres (1940) saw them tearing open the nests of tent caterpillars, devouring large quantities of the larvae, which were about three-quarters of an inch long.

_Behavior._--Although the black-throated green warbler is one of our tamest and most confiding wood warblers, as shown by the intimate studies of its home life made by several observers, it is much more often heard than seen, for it is a tiny mite and spends most of its time in the tree-tops, gleaning in the foliage of both coniferous and deciduous trees. As Miss Stanwood (1910b) says: "The bird is quick in its movements, but often spends periods of some length on one tree, frequently coming down low to peep inquisitively at an observer, once in a while flying toward a person as if to alight on his hand or head." Forbush (1929) draws a picture of its confidence: "Like all the wood warblers it is fond of bathing, its bath tub often some pool in a mountain trout brook. One day as I stood beside such a brook, a very lovely male, disregarding my presence, alighted on a stone at my feet, and at once hopped into the clear spring water and performed his ablutions, dipping into the stream and throwing off the sparkling drops in little showers. As he stood there in the sunlight which streamed through an opening in the tree-tops, he left an enduring picture in my memory."

Those who have studied the home life of the black-throated green warbler have noted its intolerance of some avian intruders in the vicinity of its nest, and its tolerance of others. Pitelka (1940b) writes:

On the eighth day after the hatching, a red squirrel (_Sciurus hudsonicus_) was observed to approach the blind, coming to within seven feet of the nest. At this time, the female simply left the vicinity of the nest at once and gave no alarm notes. Later the same day, when a young Black and White Warbler approached the nest to a distance of five feet, the female pounced upon it and struck with considerable force. When the intruder returned a second time the female flew at it and drove it away. The indifference to red squirrels and at the same time the offensive reaction toward small passerine intruders (_Vireo olivaceus_ and _Penthestes atricapillus_) has also been noted by the Nices (1932: 160).

Reading and Hayes (1933) write: "While at the nest, we noticed an inquisitive Chestnut-sided Warbler in a maple a short distance away. He hung around for several minutes, peering at us, until suddenly the male, ably seconded by his mate, attacked him and drove him off. A male Blackburnian met the same fate a little while later, while peacefully hunting insects in the big spruce and, about an hour after that a Red-eyed Vireo changed his intended route at the first warning note and promptly withdrew. Curiously enough, a small family of Black-capped Chickadees travelling slowly through the spruce was totally disregarded."

The black-throated green warbler is seldom bothered by the cowbird, although mentioned by several writers as imposed upon.

_Voice._--Aretas A. Saunders has sent me the following full account of the two songs of the black-throated green warbler: "The quality of the songs is sweet and musical and exceedingly pleasing. With the possible exception of the yellow warbler, this species has the most attractive of the _Dendroica_ songs. The quality has something indescribable that is all its own and enables those familiar with it to recognize the song, however variable the form.

"The black-throated green warbler has two distinct forms of song. Both may be sung by the same individual, and both are equally common in the migration and through the nesting season, so that they cannot be considered as territory and nesting songs. I distinguish them as first and second, but my choice is purely arbitrary. Both are delivered in the same quality. The first is a little longer than the second, for it contains more notes; but it is not proportionately longer, for the notes are shorter.

"The first song has notes on three different pitches. The first notes, three to nine but commonly four or five, are all on the same pitch, usually the highest; the next note, usually a major third lower, is the lowest; the next, and last, is between them. Such a song might be written _sree sree sree sree sree tro tray_, all the notes being of equal length. I have 34 records of this song, 23 of which follow this form. A few are arranged with the last note highest, or lowest, or on the same pitch as the first. The first notes are sometimes varied by alternating short and long notes or sometimes are united in a long trill.