of construction to its completion and the laying of the first egg,
covering a period of 4 days.
Construction was first observed at 7:45 a. m., on June 12, 1939, when a
female Yellow Warbler was seen carrying a tuft of plant-down into a
small boxelder sapling. Upon examination, a mass of plant-down about one
and one-half inches in diameter was found at a measured height of two
feet three inches from the ground in the fork of the sapling. During an
hour of observation the female continued to carry plant-down at
intervals of about four minutes although once it did not bring any
material for twenty minutes. At noon the plant-down mass had increased
to about three inches in diameter and was more compactly pushed into the
fork. By 6:45 p.m., there were many strands of plant fibers and grasses
woven around and through the plant-down in such a way as to wrap and
bind the plant-down around the small twigs of the fork. The nest was
just assuming a cup-shaped structure. The female was now bringing large
loads of a mixture of grasses and plant fibers and working at a rate of
about one trip every four minutes. The first day's building was
completed at 7:55 p.m. The nest was now partially surrounded with woven
plant fibers and grasses with a slight formation of a rim.
On the second day the work continued and the "rim consisted of plant
fibers and grasses woven partly into the original down but mostly into
the sides and around the top. At 6:45 p.m., the nest appeared completed
with a well-formed cup, plant-fiber and grass rim, and a plant-down
floor." The third day was partly rainy and little was accomplished but
"by 8:00 on the fourth morning, the plant-down inside the nest was
smoothed out and contained a few strands of fine grasses. * * * During
all the observations on the building of this nest the male at no time
was seen to bring any nest material. However, since there were many
hours during the day when no observations were made, it is possible that
he might have helped at some time. * * * At 6:30 a.m., the following
day, one egg was found in the nest. * * * The dates of the beginning of
construction and the dates the first eggs were laid were obtained for
two other nests, and the time which elapsed in both cases was four
days."
Only the female was seen to take part in the building of the nest that
Mr. Smith (1943) watched, but my experience was somewhat different. On
May 10, 1942, I found a pair of yellow warblers building a nest in the
top crotch of a blueberry bush, close to the side of a country road.
They were very tame and gave me an unusual opportunity to watch them for
over an hour at short range. I parked my car within 5 feet of the nest
and took motion and still pictures, with cameras even nearer. The nest
was nearly done and they were putting in the lining. Both birds helped
in the work, but the female did nine-tenths of it. She came at frequent
but rather irregular intervals, bringing a billful of soft plant down
that looked like the down from ferns, some of which I found growing
nearby, and to which I saw her making frequent trips; the fronds of the
cinnamon ferns were just unfolding. This material she deposited in the
cup of the nest and settled her body down into it, smoothing the lining
into place by turning her body around in different directions, pressing
it down with her body and up against the sides of the cup with a
sidewise motion of the wings. Occasionally she reached over the rim of
the nest, smoothing it with her neck and tucking in the loose ends with
her bill. The bottom and outside of the nest seemed to be about
finished; one side of it, opposite the most exposed side, was anchored
to a nearby twig with strands of plant fiber. The female seemed utterly
fearless; the male was more shy, but his streaked breast was
occasionally seen at the nest.
Robie W. Tufts tells me that he has seen the male at the nest; he saw a
male come to a partly finished nest sit in it for over a minute as
though testing the workmanship and sing twice while sitting there. The
male is always very attentive during nest-building, following his mate
back and forth on her trips for material and keeping close to her most
of the time. His interest in the nest is so keen that it would be
strange if he did not sometimes help.
The eastern yellow warbler builds a neat, strong nest, the materials
being firmly and smoothly interwoven and the lining compactly felted.
Five local nests before me show quite a variation in the materials used
and in their arrangement. The most obvious material, occurring more or
less in all of the nests, consists of the silvery-gray strands from the
last-year's stalks of milkweed, Indian hemp, or other similar dead
weeds. One nest has a great mass of such material below it on one side,
evidently to fill in space in the fork that supported it; mixed with
this material are a few strands of grasses, other shredded weed stems,
bits of wool, and gray fur. Although this nest is far from neat
externally, the cup of the nest is well and firmly made of finer silvery
fibers and fine grasses, cinnamon-fern down, with which it is profusely
lined, and a few fine white hairs. The rim is strongly reinforced with
horsehair and decorated with the cinnamon down. This nest, the largest
of the lot, measures nearly 5 inches in height and 3 inches in diameter,
externally. The smallest and the neatest of the five is made of finer
strands of similar materials, without a trace of cinnamon-fern down, the
whole being very firmly and smoothly woven into a compact little nest;
the rim is neatly made of very fine grasses, and it is smoothly lined
with white plant-down; it measures only 2 inches in height and 2-1/4
inches in diameter, externally. Grasses enter largely into the
construction of all the nests. One in particular is lined with both
white and buff plant-down and a little very fine grass, and has a
solidly built rim of strong grasses very firmly interwoven; the
foundation consists of dry brown and gray lichens, or mosses, and a lot
of cotton waste, such as is used to clean machinery. A two-story nest,
which measures 4 inches in total height, is profusely lined with white
cotton in both stories. There is little difference in the internal
measurements, which vary from 1-3/4 to 2 inches in diameter, and from
1-1/4 to 1-1/2 inches in depth.
None of my nests contain any feathers, but Dr. Roberts (1936) tells of a
nest that was made entirely of chicken feathers, with "not a bit of
material of any other kind." It was built in a jewelweed (_Impatiens
capensis_), but after a brisk wind and a sharp shower both nest and weed
were completely wrecked. He shows a photograph of a nest built almost
entirely of sheep wool, and speaks also of the use of fine strips of
inner tree bark, which probably occur in many nests, of quantities of
fine, white, silky pappus from various plants, and of a few feathers. Du
Bois mentions in his notes a nest in which five soft, white chicken
feathers were woven into the lining, the largest one when stretched out
measuring 3-3/4 inches; there were also two or three feathers in the
body of the nest. In my collection is a beautifully camouflaged nest
that was built in the upright crotch of a small poplar and seems to be
made very largely of white cotton mixed with fine, light-colored fibers.
It is lined with cotton, and with a few green poplar leaves fastened to
the exterior, the whole being firmly bound with some of the finest
fibers and with spider silk, the light-colored material matches the bark
of the tree so closely that it might easily be overlooked.
T. E. McMullen has sent me his data for over 40 nests of the eastern
yellow warbler found in New Jersey and Pennsylvania. The lowest nest was
only 1 foot from the ground in a small bush, and the highest was 30 feet
up in an elm. In addition to the shrubs and trees mentioned above he
lists arrowroot, blackberry briers, elder, holly, Osage-orange and
button-bushes, birch, wild cherry and oak saplings, and a pear tree.
The well-known habit of building nests one or more stories over
cowbirds' eggs will be discussed under the enemies of the yellow
warbler.
_Eggs._--Four or five eggs made up the usual set for the eastern yellow
warbler; sometimes as many as six are found, or as few as three. In
shape, they vary from ovate to short ovate, or rarely show a tendency to
elongate ovate. They are only slightly glossy. These handsome eggs show
a great variation, both in ground color and in markings. The most common
ground colors are grayish white or greenish white but some eggs have a
bluish white or even a soft, pale green ground color. The spots and
blotches show an even greater variety of colors. Shades of "fuscous,"
"olive-brown," "citrine drab," "buffy brown," "buffy olive," "light
brownish olive," "raw umber," "metal bronze," or "tawny olive" are
intermingled with undertones of "deep gull gray," "neutral gray,"
"purplish gray," "pale purplish gray," "mouse gray," or "buffy brown."
The markings tend to form a wreath around the large end where, on the
heavily-marked types, the blotches overlap the undertones and an almost
endless number of shades are formed. Sometimes a few spots or scrawls of
dark "mummy brown" or "olivaceous black" stand out in sharp contrast to
the other markings. Although the eggs are usually well marked,
sometimes with blotches a quarter of an inch in diameter, often they
are only finely speckled with the gray undertones. The measurements of
50 eggs average 16.6 by 12.6 millimeters; the eggs showing the four
extremes measure =17.8= by 13.2, 17.8 by =13.7=, =15.2= by 12.7, and
15.8 by =11.7= millimeters (Harris).
_Young._--The incubation period for the eastern yellow warbler has been
recorded as from 8 to 11 days (most observers place it as about 11 days
for each individual egg); often, but not always, it begins before the
set is complete, making the period appear shorter for the first egg
laid. Eggs are generally, though not always, laid on successive days,
but at times 1 or 2 days intervene between layings. Incubation is
performed wholly by the female. The male stands guard near the nest and
feeds the female while she is sitting, but she also leaves occasionally
to feed herself. The young remain in the nest from 8 to 15 days,
according to several observers, but here again the normal time is
probably between 9 and 12 days, if they are undisturbed.
Harry C. Bigglestone (1913) describes the hatching process as follows:
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.