Part 22

At about 5:30 a.m. on July 3 the writer was attracted by a peculiar rolling motion of the egg in the nest, and noticed upon closer observation, that the shell bulged out in a ring around the middle or a little nearer the smaller end; and soon it began to crack at this place. The egg raised on the small end, leaning against the side of the nest, and the young bird freed himself from the shell by a series of pushes and kicks by the head and feet, respectively. The head escaped from the larger part of the shell and the lower part of the body from the smaller end. The crown of the head and the median line of the back of the nestling were downy. This entire process covered a period of less than four minutes.

The empty shells were broken up and eaten by the parents. He says that brooding was carried on entirely by the female, except that he once saw the male brooding for 7 minutes, and adds:

The female was more careful in brooding the young during the first few days. She would stop for intervals throughout the day, while feeding, and brood the young. Her way of completely covering the brood was to fluff out the under coverts against the rim of the nest and bring the wings down, just inside, so as to effectually close the nest.

* * * The female had different brooding attitudes for the varying circumstances. For protection against the cold of early morning she brooded in the manner described above, completely covering the young. Through the rains she brooded in much the same way as for cold, sheltering the young, so that after an unusually heavy downpour, the nest remained perfectly dry inside. During the heat of midday she usually stood in the nest with wings spread, shielding the young, but without shutting off the circulation of the air. On the contrary, at times she gently flapped her wings, as if fanning the young. During the strong winds she stood in the nest with wings outstretched, and leaned in the direction of the wind, so as to secure a delicate balance and at the same time keep the young in the nest.

Feeding of the nestlings was carried on about equally by both male and female parents for the first 7 days, after which the male was frightened away by a snake and did no more feeding, the female carrying on for the next 4 days. During observations covering nearly all of 10 full days and part of another there were 2373 feedings, 813 by the male and 1560 by the female, there being only 33 feedings during the whole of the last day. "During the first three or four days when the female was brooding, usually the male gave her the food, which she distributed to the nestlings." Some of the food had to be broken up before it was given to the young; and sometimes it had to be thrust down their throats. There were 331 feedings of unrecognized food, and 553 of unidentified insects. The identified food consisted of 659 green worms, 326 fly worms, 162 other worms, 147 May flies, 103 moths, 75 millers, 65 mosquitoes, 26 larvae, 25 grasshoppers, 23 spiders, 18 ants, 14 grubs, 8 beetles, 4 damsel flies, 2 tree hoppers, and 1 bee. Feeding began at from 4:29 to 4:50 a. m., and ended at from 7:36 to 8:04 p. m., the average feeding period being 15 hours and 30 minutes per day. The parents were not seen to follow any system of rotation in feeding the young. "At no time while the nest was under observation did the parents feed by regurgitation," though the parents on several irregularly occurring occasions were seen to insert an apparently empty bill into the mouth of a nestling, but it was long after hatching. The excreta were removed by both parents; they were eaten during about the first half of the nest life and carried away after that; the female did most of this. The parents were very watchful of the young, and were seen to drive away such birds as the cowbird, blue jay, wren, chickadee, brown thrasher, kingbird and blackbird, if they came too near the nest; the only bird that was not driven away was a catbird. The presence of a garter snake at the base of the bush caused great excitement; the snake was seen to climb up into the bush and carry off one of the young when it was about six days old; the young bird was dead before it could be rescued.

Schrantz (1943) writes: "The Yellow Warblers are hatched naked except for a scanty amount of down and are an interesting sight with their large bulging eyes and abdomen. It was observed that the eyes were commencing to open on the third day after hatching. By the fifth day the young can completely open their eyes, but in many cases would immediately close them when the nest was approached. At this age they would also duck down in the nest as if trying to hide. A slight tapping on the nests would cause a rapid outstretching of necks with open mouths." Bigglestone (1913) found that almost any slight noise near the nest would produce the same results. Studies of weights by Schrantz showed that--

the young averaged, when hatched, 1.27 gms.; at one day old, 1.87 gms.; at two days old, 2.95 gms.; at three days old, 4.36 gms.; at four days old, 5.57 gms.; at five days old, 7.26 gms.; at six days old, 8.20 gms.; and at seven days old, 8.78 gms. * * *

Of the 168 eggs in forty-one nests, 119 eggs, representing 70.83%, hatched. Thirty-four eggs, representing 20.24%, disappeared due to wind, abandonment of nest, and unknown causes. Fifteen eggs, representing 8.93% were addled, two of which were buried with a Cowbird's egg. Of the 119 nestlings, twenty-eight disappeared. This represents 16.66% of all eggs laid. Four of them were seen dead in the nests. The others disappeared from unknown causes. Therefore a total of 91 fledglings, representing 54.17% of the original 168 eggs, left the nest. * * *

After all the young left a nest, the parent birds could be found feeding them in the immediate vicinity of the nest for a period of about three days. After this time the birds became more dispersed from the nesting site, but could still be found in the vicinity for a week or ten days.

An unusual casualty is recorded in the following note sent to me by Dr. Harrison F. Lewis: "A nest of this species which I found in a sheep-pasture, was largely built of wool, presumably gathered from the neighboring bushes, where it had been left by the sheep. One of the young birds in this nest died as a result of having threads of the wool in the nest become entangled about its tongue and bill. Another member of this brood became entangled in a similar fashion, but I released it."

_Plumages._--Dr. Dwight (1900) calls the natal down "mouse-gray," and describes the juvenal plumage, in which the sexes are alike, as "above, pale olive-brown. Wings clove-brown broadly edged with bright olive-yellow paling at tips of the quills, the edge of the outer primary bright lemon-yellow. Tail pale clove-brown, the inner webs of the rectrices lemon-yellow, the outer edged with olive-yellow. Below, pale sulphur-yellow, unstreaked."

The first winter plumage is acquired by a partial postjuvenal molt early in July that involves the contour plumage and the wing coverts but not the rest of the wings or the tail. He describes the young male as "above, pale yellowish olive-green, the edgings of the wing coverts paler. Below, dull lemon-yellow obscurely, narrowly and sparingly streaked on the throat and sides with pale chestnut." The female is paler throughout and has no streaking.

The first nuptial plumage is acquired by a partial prenuptial molt in early spring, "which involves most of the body plumage, the wing coverts and the tertiaries, but not the primaries, their coverts, the secondaries, nor the tail. The whole plumage becomes golden lemon-yellow, greener above and [in the male] brightly streaked on the throat, breast and sides with pale chestnut, somewhat veiled by the feather edgings. The forehead and crown are yellower than the back and usually chestnut tinged. The tertiaries and wing coverts are broadly edged with bright lemon yellow." The female in this plumage is yellower than in the fall and has a few obscure chestnut streaks below. Old and young birds are now very much alike, often practically indistinguishable, except for the worn juvenal wings and tail.

Adults have a complete postnuptial molt in July before or while they migrate and a partial prenuptial molt, as in the young bird, before they arrive in the spring. In El Salvador, according to Dickey and van Rossem (1938), "both adults and young of the year were in complete fall (postnuptial) plumage by the time they arrived. * * * An adult male taken April 10 is in the midst of the spring (prenuptial) molt and presents an extremely ragged appearance. Another, collected on April 24, has entirely finished this molt."

In both adult male and female plumages the colors are richer and the streakings below heavier than in the young bird, but the female is always duller in color and the streaking is less prominent or entirely missing.

_Food._--Edward H. Forbush (1907) writes of the food of the eastern yellow warbler in Massachusetts:

It would be hard to find a summer bird more useful among the shade trees or in the orchard and small-fruit garden than this species. Almost entirely insectivorous, it feeds on many of the greatest pests that attack our fruit trees, vines and berry bushes. Whenever the caterpillars of which it is fond are plentiful, they form about two-thirds of its food. It is destructive to the small caterpillars of the gipsy moth and the brown-tail moth, and is ordinately fond of canker-worms and other measuring worms. Tent caterpillars are commonly eaten. Small bark beetles and boring beetle are eaten, among them the imago of the currant borer. Weevils are greedily taken. A few useful beetles are sacrificed; among them ground beetles, soldier beetles, and small scavenger beetles. The Yellow Warbler has some expertness as a flycatcher among the branches, and seizes small moths, like the coddling moth, with ease, but apparently does not take many parasitic hymenoptera, although some flies are taken. Plant lice sometimes form a considerable portion of its food. No part of the tree where it can find insect food is exempt from its visits, and it even takes grasshoppers, spiders, and myriapods from the ground, grass, or low-growing herbage.

He (1929) says elsewhere: "It attacks none of the products of man's industry, so far as our records go, except the raspberry, of which it has been known to eat a few occasionally."

S. A. Forbes (1883) reports that 5 stomachs from a canker-infested orchard contained 94 percent insects; of which 66 percent were canker-worms, Coleoptera 23 percent, spiders 6 percent, Hymenoptera 2 percent, and Hemiptera 1 percent. A. H. Howell (1907) found a cotton-boll weevil in one stomach from Texas; E. R. Kalmbach (1914) reports that of seven Utah stomachs, two contained alfalfa weevils, forming 25 percent of the food in one; and Prof. Aughey (1878) found an average of 11 locusts in 7 Nebraska birds.

_Behavior._--The gentle little yellow warbler is not only one of the prettiest but one of the tamest and calmest of our bird neighbors. It comes to us in the most friendly and confiding manner to build its cozy nest and rear its little golden family in the lilac bush under our window or in the climbing rambler over our porch. Nor does it mind our company in the least as we watch its home life almost within arm's reach. I have sat for an hour within a few feet of a pair of these lovely birds and watched them building their nest. The many fine photographs that I have received show that it is an easy subject for close-up pictures; the near presence of the camera does not seem to disturb them in their feeding routine. Many intimate home-life studies have been very successful, for they are brave and devoted parents. Robie W. Tufts (1927) has had a male yellow warbler come at least twice to feed a brood of young that he was holding in his hand, and once he even wiped his bill on his thumb. It is such displays of confidence that endear us to the little golden gem.

_Voice._--Aretas A. Saunders contributes the following study of the song of this warbler: "The song of the yellow warbler is a bright, sweet and musical refrain of about 8 notes. My records show that the number varies from 5 to 15 and averages 8-1/2. The songs are quite variable in form, so much so that it is the quality, rather than the form, that makes the song recognizable. This quality is difficult to describe, yet that quality, after a little familiarity, is easily recognized; the tones, though musical and pleasing, are not quite clear, but slightly sibilant.

"Two forms of the song are fairly typical, but there are a number of others that vary so much that they are quite unlike either of these. The most common form begins with four or five notes of even time, and all on the same pitch. These are followed by two or three more rapid notes on a different pitch, usually lower; and the song is ended by one or two notes back on the original pitch and time. Such a song, in its simplest form, might be written _see see see see tititi see_. Of my 87 records, 45 may be classed as this form.

"The second form begins in the same manner, but has all the notes of equal time, and the last three or four successively lower in pitch. I have records of 24 such songs. There remain in my records 18 songs so variable that they belong to neither of these forms, and yet no two of them are similar in form. A number of songs of the different forms begin with slurred notes, the slurs being about equally up or down in pitch.

"Songs vary from 1-1/5 to 2 seconds in length, averaging about 1-2/5 seconds. The pitch varies from A´´´´ to D´´´´´, only three and a half tones altogether. Single songs vary from one to two and a half tones in range of pitch, averaging about one and a half tones. Individual birds may sing as many as three different songs, and sometimes sing two different songs in regular alternation.

"Singing continues from the first arrival in migration until the third week of July, ceases for a short time, but is usually revived in August, and is to be heard irregularly until the birds depart for the south."

Francis H. Allen gives me his impressions of the two common songs as follows: "One of these I have been accustomed to render as _wee see wee see wiss wiss´-u_. Occasionally the final _wiss´-u_ is doubled. The other of these two songs goes something like _wee wee wee witita weet_, without the drop in the pitch that the first song has at the final note. I have also heard a song of five single notes with no variation in pitch or tempo--_weet weet weet weet weet_. Besides a rather sharp _chip_, which is the ordinary call-note, I have heard a _dzee_ from a yellow warbler."

The yellow warbler is an early riser. Mr. Smith (1943) heard one begin singing at 4:56 a.m., "daylight time," and another at 4:05, "but with only one song until 4:08 when seven were given during the space of one minute. During the song period of fifty minutes, 197 songs were given." Dr. Charles W. Townsend told Mr. Allen that he heard one at Ipswich, Mass., on June 13, 1908, that began singing at 3:10 a.m., but this was standard time.

Dr. Winsor M. Tyler (1937) mentions a peculiar note, heard during the migration in August, which had puzzled him for nearly 30 years until he finally traced it to an eastern yellow warbler. "As we walk under the trees, listening, we hear a long, wild, high, sharp bird-note, abrupt, and very slightly vibratory, lasting perhaps half a second. It is a characteristic sound of this time of year, and we hear it best on these quiet, silent days. It comes from a bird moving restlessly up in the trees, and before we can see the bird, it is gone. * * * In pitch, it suggests the call of a migrating Ovenbird, but it is too long-drawn-out; it suggests the _chip_ of a Northern Water-Thrush in its sharp abruptness, but again it is too long."

According to Albert R. Brand (1938) there is considerable variation in the pitch of the song of the eastern yellow warbler, from 8,775 vibrations per second in the highest note to 3,475 in the lowest note, and with an approximate mean of 5,900 vibrations per second. This is far below the approximate mean of 8,900 for the black-poll warbler, but well above the average of 4,000 for all passerine birds.

_Field marks._--One hardly needs field marks to recognize a yellow warbler; it is the yellowest of all our warblers at all seasons, even the wing and tail feathers are edged with yellow, and there is no white in either wings or tail. The youngest birds likewise show some yellow on the under parts and in the flight feathers. See the descriptions of plumages for details.

_Enemies._--The arch-enemy of the yellow warbler is undoubtedly the cowbird. This warbler is one of the very commonest victims of this parasite, and comparatively few of its nests are not visited at least once by a cowbird in regions where the latter is very common. Dr. Friedmann (1929) has about 500 records of such imposition on the eastern yellow warbler. Everyone who has examined nests of this warbler in any number has found one or more eggs of the cowbird in some of the nests. This parasitic habit has cost this species of warbler many extra hours of unexpected labor and the loss of many eggs and young. But the most interesting fact about it is that the warbler has found a way to combat the evil and, in many cases, to defeat the plans of the cowbird, by either deserting the nest in which the strange egg is deposited or by building a second floor over it and leaving the alien egg to cool off in the "cellar."

The yellow warbler is not the only bird that has learned to do this occasionally, but it is the only one that does it regularly and persistently in spite of repeated contributions from the cowbird. Even if the warbler has one of its own eggs in the nest when the cowbird's egg is deposited it may bury both the eggs by building a story above them, but if there are two or three warbler's eggs in the nest before the alien egg appears, the warbler may feel obliged to incubate and hatch out the stranger, with the usual results of her own young being crowded out and lost. Two or more cowbird's eggs are almost sure to be deserted or buried. But the cowbird is very persistent and keeps on laying, as successive stories are added to the nest by the energetic and persevering warblers. Two-story nests are very common, and as many as three, four, five, and six stories have been recorded. Mr. Forbush (1929) was told by Dr. H. F. Perkins "of one case where a six-storied nest was built, with a cowbird's egg in every one." Mr. Du Bois tells me of a new nest he found in a low bush, with another nest, about half completed and only about a foot below it, containing a fresh, cold cowbird's egg. Out of 43 nests found by Dr. George M. Sutton (1928) in Pymatuning Swamp, Pa., "a Cowbird egg was found in only one nest. This is most unusual, but is due, as elsewhere stated, to the protection against these parasites afforded by the Red-winged Blackbirds which would not tolerate a Cowbird anywhere about the marshes."

Snakes sometimes destroy the young, as related above; squirrels, blue jays, and other predatory mammals and birds rob the nests; and the adults must always be on the alert to escape the many enemies that prey on all small birds.

Harold S. Peters (1936) records only one louse, _Philopterus subflavescens_ (Geof.), as an external parasite on the eastern yellow warbler.

_Fall._--The striking feature of the fall migration of the eastern yellow warbler is its earliness. The birds begin to move away from their nesting haunts as soon as the young are able to take care of themselves, and the southward migration is well under way before midsummer. Smith (1943) says that, in Vermont, "during many seasons, the species is not seen later than July. Departure dates for local summer residents range from July 15 to the 30th. Later records occur between August 18 and September 9th." These later records are probably for birds from farther north. There seems to be a wide spread between the times that the earliest and latest birds leave.

Dr. L. H. Walkinshaw writes to me: "To me it is interesting how soon after nesting has been completed these warblers disappear. After July 10, it is very hard to find one of the species here in Michigan, and after August 10, almost impossible. It does stay some in certain good feeding areas, but the majority have left long before August." According to Milton B. Trautman (1940), the migration in Ohio begins early in July, reaches its height during the first half of August, and only stragglers are seen after September 10.

Arthur T. Wayne (1910) says that, in South Carolina--

the Yellow Warbler is positively uncommon during the spring migrations, but exceedingly abundant in summer and autumn. * * * By July 4, the return migration takes place and a few young birds arrive, but it is not until the 10th or 15th that they are common. * * * The habits of the birds are entirely changed, however, in summer and autumn, for then they frequent the cotton fields, as well as lands which have been planted with peas for forage. It is also not unusual in autumn to see as many as twenty or more of these little birds far out in the salt marshes, where they find food in abundance. The species is so very abundant in late summer and autumn that it is not unusual to encounter hundreds of individuals in a few hours on plantations or in close proximity to salt water.

Prof. W. W. Cooke (1904) writes: "Though in migration the yellow warbler occurs in Florida as far south as Key West and is sometimes fairly common in northern Florida, the numbers that migrate through the southern part of the State must be very small, for not a bird passing north or south has been reported from any of the Florida lighthouses. The migration route of the yellow warblers that breed near the Atlantic coast is evidently southwest to northern Georgia and Alabama, and then across the Gulf of Mexico."

Perhaps the main flight from Florida and the other Gulf States is across the Gulf to Yucatán and then down through Central to South America, for there seem to be no records for Cuba for the eastern yellow warbler. There is a regular migration along the coast of Texas. Dickey and van Rossem (1938) say that "the eastern yellow warbler migrates through El Salvador in fair numbers, but no specimens were taken at any time during the winter. In the fall, particularly, great numbers are in evidence. The first arrivals reached Lake Olomega on August 1, but the main body did not begin to drift through until about the middle of that month."

Frederick C. Lincoln (1939) remarks: "Redstarts and Yellow Warblers, doubtless the more southern breeders in each case, have been seen returning southward on the northern coast of South America just about the time that the earliest of those breeding in the North have reached Florida on their way to winter quarters."

_Winter._--Dr. Alexander F. Skutch contributes the following winter notes: "This morning as I sat at breakfast a yellow warbler flitted among the shrubbery outside the window. Here in Central America, through 8 or 9 months out of the 12, this well-known bird occupies the same place in dooryard, garden, hedgerow and scrubby pasture as during its briefer sojourn in the more northerly regions where it nests. None of the resident warblers of Central America is quite so abundant and familiar about human dwellings. Everywhere it avoids the heavy forest and prefers the sunlight that floods the clearings made by man.