Part 18

Eggs.--From 4 to 7 eggs may be found in the nest of the blue-winged warbler; 5 seems to be the commonest number, and sets of 6 are not very rare. The eggs are ovate, with a tendency to short ovate, and they have only a slight gloss. The white ground color is finely speckled or sparingly spotted with "chestnut brown," "mummy brown," and "sayal brown," with under markings in shades of "drab-gray." Some sets have three or four eggs that are almost immaculate, with one egg sparingly spotted; other sets occasionally are prominently spotted with "drab-gray," "light Quaker drab," and "dark vinaceous-drab," or, less often, with spots of dark "mummy brown." Usually the majority of the markings are confined to the large end. The measurements of 50 eggs average 15.7 by 12.5 millimeters; the eggs showing the four extremes measure =16.8= by =13.0= and =14.2= by =11.6= millimeters (Harris).

Young.--An egg is laid each day until the set is complete, and incubation generally begins when the last egg is laid. The period of incubation is 10 or 11 days, and the young remain in the nest from 8 to 10 days. Mr. Burns gave Dr. Chapman (1907) the following full account of the nest life:

The task of incubation falls on the female alone. It appears that an airing is taken in the early morning or a little before midday, and again in the early evening, though perhaps not regularly every day. I have not seen the male about the nest with food at this period. The female will allow a close approach, looking into one's eyes with that hunted look so common in wild animals, and often flushing without a protesting note. The period of incubation in the one instance was exactly ten days.

On June 13, at 6.30 p. m., five young just hatched were blind, naked and prostrate from chin to sternum. The shells were disposed of immediately, in what manner I am unable to state; the female was reluctant to vacate.

On June 15, at 2.45 p. m., the young were able to raise their heads slightly and a fluffy bit of down had appeared about the head, also a dark stripe along the back bone. The female appeared, accompanied by the male, and fed the young with small green larvae--such as may be found on the under-side of oak and chestnut leaves--and then shielded the callow young from the hot rays of the sun.

On June 16, at 6.30 p. m., when the young were three days old, a downy puff appeared between the shoulders, wing quills being dark. The strongest bird had the eyes partly open and the mouth wide open for food.

On June 18, at 7 p. m., the heads and bodies were no longer flesh-colored but were well enough covered to appear dark. The eyes were open. At a cluck from me their mouths flew open. Both parents fed them with green-colored larvae. When the male rested a moment on a brier above the nest, the female flew down and drove him away, fed the young, re-appearing with excrement in her beak, which was carried in an opposite direction from the regular approach via maple bough and poplar sapling. The male fed the young from a mouthful of very minute larvae or eggs, which were gathered from the silken nests in the unfolding leaves of a nearby poplar; after this (7.30 p. m.) the female covered the young for the night.

On June 20, at from 6.50 to 7.35 p. m., the young had been seven days in the nest. They were well feathered and of a yellowish-green cast, the short tails being tipped with yellow. The parents were more suspicious. The female came to the maple bough with something in her beak and flew down to the briers and back again several times before she dropped to the edge of the nest and fed her young. The male appeared immediately but swallowed a green grub himself upon discovery of me twenty-five feet away. The female came again in five minutes with a brownish object in her bill, but appeared more timid and refused to drop to the nest until the male set her an example of courage.

On June 21, at 6.12 p. m., the young were fully fledged in green plumage above and dirty yellow beneath. They showed fear of me for the first time, eyeing me in the same manner as the parent bird when on the nest. They were evidently ready to vacate at a moment's notice or hasty movement on my part. The parents appeared, scolding rapidly. The female fed the young as soon as I retired to my old stand under a bush, with a rather large green grub (6.20 p. m.) and flew out to the top of a blackberry bush, followed immediately by the topmost fledgling. It could do little more than run. The adults flew to within a yard of my head, making a great outcry, and in the midst of the excitement the remainder of the young vacated the nest with feeble chips. The male gave his attention to them, while the female followed me as I beat a hasty retreat to enable them to collect their little family before dark. Eight days had elapsed since incubation was completed, and it is not at all unusual for the young of this species to leave the nest while so tiny and ragged.

Plumages.--Dr. Dwight (1900) calls the natal down "mouse-gray," and describes the juvenal plumage, in which the sexes are alike, as, "entire body plumage olive-yellow darkest on the back and throat. Wings and tail slate-gray largely edged with plumbeous gray, the tertiaries and coverts with olive-yellow; the greater and median coverts tipped with white, yellow tinged. Rectrices largely white. Lores dusky."

A partial postjuvenal molt begins early in July, involving the contour plumage and the wing coverts, but not the rest of the wings or the tail. This molt produces the first winter plumage in which the sexes are very much alike, the female being duller in color, especially the streak through the eye, and having less yellow on the crown. Dr. Dwight (1900) describes the first winter male as "above, bright olive-green, lemon-yellow on the crown veiled by greenish tips. Below, bright lemon-yellow, the crissum white or merely tinged with yellow. Transocular streak black. Wing coverts plumbeous gray, edged with olive-green, the greater and median tipped with white, yellow tinged, forming two broad wing-bands."

The birds are now practically adult in plumage. The first and subsequent nuptial plumages are acquired by wear, which produces little change beyond removal of the greenish tips. Subsequent winter plumages are acquired by a complete postnuptial molt each July.

The interesting hybrids between this and the golden-winged warbler are discussed on pages 3 and 4. Kumlien and Hollister (1903) mention a probable mating of this with the Nashville warbler.

Food.--Nothing seems to have been published on the food of the blue-winged warbler beyond that mentioned above as food given to the young, which is doubtless eaten by the adults as well. It is apparently wholly insectivorous, seeking its food near the ground in the weed patches and underbrush where it lives and among the lower branches of the trees in its haunts. Probably any small insects that it can find in such places, as well as their larvae and eggs, including many small caterpillars, are eaten. Small grasshoppers and spiders are probably included. Prof. Aughey (1878) observed it catching small locusts in Nebraska. It is evidently a harmless and a very useful bird in destroying insects that are injurious to foliage.

Behavior.--Dr. Chapman (1907) writes: "It is rather deliberate in movements for a Warbler, and is less of a flutterer than the average member of the genus Dendroica. Some of its motions suggest those of the tree-inhabiting Vireos, while at times, as the bird hangs downward from some cocoon it is investigating, one is reminded of a Chickadee." And he quotes Burns as follows:

Perched inconspicuously near the top and well out on the branchlets of a tree or sapling, preferably facing an opening, if in a thicket; it is in itself so minute an object as to be passed unseen by many, more especially as it is much less active than most of our Warblers. With body feathers puffed out to a delightful plumpness, except for the backward sweep of the head while in the act of singing, it remains motionless for quite a while. When it moves it is with a combination of nervous haste and deliberation, and its song may be heard from quite another part of the landscape with no apparent reason for the change. While it has its favorite song perches, it is quite a wanderer and not infrequently sings beyond possible hearing of its brooding mate, but oftener within fifty to two hundred feet of the nest.

Voice.--Aretas A. Saunders contributes the following study of the songs of this warbler: "The territory song of the blue-winged warbler consists of two long, buzz-like notes, the second usually lower in pitch than the first and rougher in sound, bzzzzzzz-brrrrrrrr. The pitch interval between the two notes varies from one tone to four and a half tones, but the smaller intervals, one tone and one and a half tones, are much commoner. The second note is lower in pitch than the first in about 75 percent of my records, and higher in most of the others. In a few songs the second buzz is a double note, and one may hear both lower and higher notes from a medium distance, only the lower from a greater distance, and only the higher when very near the bird.

"The pitch is not high as compared to other warblers, ranging from C´´´ to D´´´´, one tone more than an octave. The territory song commonly begins on some note from A´´´ to C´´´´. It varies in time from 1-1/5 to 1-4/5 seconds, the first note being either equal to or shorter than the second. The second note is often twice as long as the first. In some songs the second note is broken into two notes, and in one record it is in four short notes, so that the song is essentially like that of the golden-winged warbler.

"After the birds have been on the breeding grounds for a week or two, singing of the nesting song begins. This song has the same buzz-like quality as the other, but it is exceedingly variable, considerably longer, and hardly ever twice alike. The song often begins with a series of short notes, like tsit tsit tsit, or contains such notes somewhere in the middle. There are usually long buzzes that change pitch by slurring upward or downward. On one occasion, I found a bird that sang a territory song and four different nesting songs. Often the nesting song is sung in flight. By June this song is heard about as frequently as the territory song, and in late summer, after the molt, it is the one most commonly heard.

"The song of this bird is heard from its arrival in spring until early July, when it ceases for a time. It is usually revived in late July or early August, and from then on may be heard fairly frequently until the birds depart about the last of August."

In his notes sent to Dr. Chapman, Burns describes the song as, "a drowsy, locust-like, swe-e-e-e-e ze-e-e-e-e, the first apparently inhaled and the last exhaled. * * * Another song heard on the first day of arrival, on one occasion, uttered by several males in company, possibly transients here, and may be the mating song, suggests the Chickadee's che-de-de-e, che-dee-e, and che-de-de-dee, uttered repeatedly in one form or other in excitement, and while running out on the branchlets. The call and alarm note is a rather weak chip." Dr. Chapman (1912) records a longer song, heard later in the season as "w[=e][=e]-ch[)i]-ch[)i]-ch[)i]-ch[)i], ch[=u]r, ch[=e][=e]-ch[=u]r."

Francis H. Allen tells me that the final note, ze-e-e-e-e, as rendered by Burns, "is really a very rapid series of pips, as if the bird had lips like ours and vibrated them by forcing the air through them--in other words, giving a sort of avian Bronx cheer, but high in pitch. The individual pip notes are clear, but the effect of the rapid succession is somewhat buzzy."

The songs of the hybrid forms may be like the song of either parent form, more often like that of the goldenwing, or a mixture of the two.

The flight song, as heard by Frank A. Pitelka, is recorded as follows:

tsee- zweé- zweé tzip- tzip- zee-zee-zee-zee-zee-zee- zee-zee-zee-zee-zee-zee-

The song of the blue-winged warbler is one of the high-frequency songs; Albert E. Brand (1938) gives the approximate mean as 7,675, the highest note about 8,050 and the lowest note about 7,125 vibrations per second; this compares with an approximate mean for the black-poll warbler of 8,900 vibrations per second, the highest frequency of any of the wood warblers, and an average for all passerine birds of about 4,000 vibrations per second.

Field marks.--A small warbler with a greenish olive back, yellow forehead and under parts, with a black line through the eye and two white wing bars, is a blue-winged warbler. The female is merely more dull in coloration than the male, and the young even duller. The hybrids between this and the golden-winged warbler are more puzzling, but in a general way they can be recognized; a nearly typical blue-winged warbler with a black throat is probably a Lawrence's warbler; and a golden-winged warbler without a black throat or cheek and with a variable amount of white and yellow on the under parts and in the wing-bars, is probably a Brewster's warbler. But there is an immense amount of individual variation between the two species, due to frequent crossing.

Fall.--Most of the blue-winged warblers move southward during August and September, though a few may linger in the southern part of the breeding range into October. Professor Cooke (1904) says: "Most of the individuals of the species migrate across the Gulf of Mexico, apparently avoiding Florida on the east and Texas and Vera Cruz on the west, as there is no record of the occurrence of this warbler in fall in Texas, and but one in Florida--that of a bird taken at Key West August 30, 1887." But this remains to be proved.