|
Wood Thrush
Hylocichla mustelina
Contributed by Florence Grow Weaver
[Published in 1949:
Smithsonian Institution United States National Museum Bulletin
196: 101-123]
The nature lover who has missed hearing the musical bell-like
notes of the wood thrush, in the quiet woods of early morning or
in the twilight, has missed a rare treat. The woods seems to have
been transformed into a cathedral where peace and serenity abide.
One's spirit seems truly to have been lifted by this experience.
These birds are found in low, cool, damp forests, often near
streams. This probably follows because of the need of mud and damp
plant material, which are used in the construction of the nest.
Undergrowth and the presence of saplings seem to help determine
the suitability of an area during the breeding season. I found no
nests in conifers, which were numerous in the mixed coniferous and
deciduous forests in which my studies of this species were carried
on, but short dead branches of these trees were often used as song
perches. There are citations in the literature, however, that
record nests in conifers. A hemlock was used in New York, cedars
in Florida, and recently many nests have been found in coniferous
bogs in northern Michigan; two nests were found in balsam firs.
Thickets were usually not chosen by the wood thrush, although one
pair built in a sapling ash-leaved maple in a dense growth of such
saplings.
Dr. A. A. Allen (1934) believes that this bird dislikes bright
sunlight, probably because its eyes are so large that too much
sunlight makes the bird uncomfortable, so that it keeps to thick
woods or ravines where there is plenty of vegetation and resulting
shade.
Besides the locations already mentioned, a number of birds
choose places near human habitations, or in parks or gardens.
Tracing this adaptation of habitat back through the literature, it
seems that this change took place during a 20-year period, from
1890 to 1910. Widmann (1922) reports a nest inside the
conservatory in Shaw's Garden, St. Louis, Mo. Orchards are seldom
chosen as locations for nests.
There is considerable evidence of the gradual northward
extension of the breeding range of the wood thrush. In reviewing
the literature for this paper, I find a recent breeding record for
Montreal, Quebec, Canada, which is a little north of previous
records for the vicinity (Cleghorn, 1940).
Root (1942) reports records for Cheboygan County in northern
Michigan in Canadian Zone coniferous bogs. Roberts (1932) has
noted the northward spread of this bird into the Canadian Zone in
Minnesota. Dr. Fred Lord in Hanover, N. H., has witnessed the
northward spread in New Hampshire, saying that 30 years ago there
were none in the village, while at the time he was writing, 1943,
they were common.
M. W. Provost (1939) writes as follows: "Before the advent
of the white man, the Wood Thrush was not found farther north than
the Lake Region in central New Hampshire and Hanover in the
Connecticut Valley. In the two decades 1890-1910 there was a
remarkable invasion of the White Mountain valleys by this bird.
Today it is by no means rare in the transition valleys throughout
the mountains and even up into the forests on slopes up to 2,000
feet. I have found a Wood Thrush on July 8, 1937, in the deep
forests of the Mountain Pond region of Chatham, at an elevation of
over 1,500 feet and three miles from the nearest settlements in
North Chatham."
This statement from Minot (1895), which is a footnote by the
editor, William Brewster, will give a basis for the comparison of
the distribution then and at the present time: "A summer
resident, very common and generally distributed in Connecticut,
less numerous and more local in Massachusetts, and rare or
accidental north of the latter State, excepting, possibly, near
shores of Lake Champlain in western Vermont, where it is said to
breed regularly and in some numbers." Goss (1891) also gives
habitat as "north to Massachusetts."
Some early records of the northward movement are as follows: A
note from F. H. Kennard, written in 1910, states that Horace
Wright recorded wood thrushes in Jefferson, N. H., which is in the
northern part of State. But Wright (1912) says that in 1904, 1905,
and 1908 the wood thrush was as yet a rare bird. He heard it
at1,600 feet. F. H. Kennard also heard these birds at Averill,
Vt., in the northeastern tip of the State, June 21, 1912, at 1,850
feet. William Brewster (1938), on May 14, 1896, heard a wood
thrush singing at the Pearly White farm, which is on the Maine
side of Umbagog Lake.
Spring.--These data are from
records in the files of the United States Fish and Wildlife
Service, which divides the range into three sections: the
Atlantic, the Mississippi, and the Western. I will deal with each
in order. Most wood thrushes have spent the winter south of the
United States. This will be discussed in more detail in the
section called "Winter." Spring migration begins
in March when birds have been reported in South Carolina, Alabama,
and Georgia, at about the 33d parallel north latitude. Some
records show that some birds are still south of the United States
at this time; therefore migration is not really in full swing
until April. There are reports of birds in North Carolina on April
3, in Maryland on April 6, in Pennsylvania, and in New Jersey on
April 11. A few early individuals have been reported for New York
on April 9 and 12. They progress northward rapidly and by the end
of April are seen in Connecticut, and by May 19 they have already
reached the northern limits of their range. They have been
reported from Vermont, Nova Scotia, and New Brunswick.
In the Mississippi Valley, in spring, wood thrushes appear in
the United States between March 26 and 30. (Audubon seems to be
the source of statements saying that the wood thrush winters in
southern Louisiana, but more recent studies do not bear him out in
this.) Ten days later they have usually advanced northward to
Dunklin County, Mo.; in the next 10 days up to April 20 they have
advanced to the parallel of St. Louis; by April 30 they have
reached Glen Ellyn, Ill.; by May 10 they average northward as far
as London, Ontario; and in the next 10 days they reach the
northern boundary of their range.
For the western part of their range, we have very few records
for the early spring months. The birds reach the southern limits
of the western flyway about April 1 and advance northward to the
44th parallel and westward to the 102d meridian by May10.
In summarizing, we find that wood thrushes appear earliest in
the Atlantic Coast States and move northward there earlier than in
the Mississippi Valley or west of it. The speed of the advance,
however, is greater in the Mississippi section than east or west
of it. In the western flyway, the birds are slow in moving
northward, but they do not move as far northward as in the other
two flyways.
Courtship and Territory.--According
to my observations, borne out by those of Brackbill (1943), the
male arrives in the territory he chooses and stays there waiting
for his mate to arrive. In one case, which I was able to watch
from the moment of arrival, the male arrived first and the female
two days later. These two birds were circling in their courtship
performance on this second day. A banded male came back to the
same territory for three years in succession. The choice of the
actual nesting site seems to be made by the female. She was seen
to alight upon a branch, hop to a crotch, stick her head barely
above the leaves, and turn around several times. This particular
spot was not chosen, however, so this may have been of no
significance.
The territory of the wood thrush may be as small as one-fifth
of an acre or as large as two acres.
In defense of this territory the wood thrushes I studied seemed
to vary in their reactions. To birds smaller than themselves they
appeared to pay little attention. Birds that disturbed the
thrushes most were other wood thrushes, veeries, and robins,
although even then reactions varied greatly. Sometimes other wood
thrushes were driven out, but at other times they were not.
Sometimes the male would challenge the intruder with a burst of
his most complete song, which would last as long as 10 minutes. On
other occasions the intruder was merely chased from the territory.
Most robins were chased, but some were not. All degrees of alarm
and retaliation were displayed from the mildest form, in which the
adult sat quietly and merely raised the feathers on the head, to a
real bird fight. When the young in one nest were 10 and 11 days
old, the male fought the most furious fight I have ever witnessed.
He flew upward attacking the robin in the air. The two birds flew
at each other with wings beating rapidly and feathers fluffed from
the body. They attacked each other over and over again, and peace
was not restored until the robin was chased from the territory. A
veery chased two wood thrushes from its territory in an area
containing five wood-thrush nests. A scarlet tanager was attracted
by the call of a young wood thrush when it was just a day out of
the nest. The tanager flew away unchallenged while another wood
thrush, which alighted on the same branch as had the tanager, was
driven out. Brackbill (1943) notes that the territory was defended
against other wood thrushes but that the birds seemed very
tolerant of other species. He says the only birds toward which
they displayed hostility were a blue jay and a purple grackle.
The males arrive first on the breeding grounds, as the records
of Cornell University show that the first wood thrushes reported
for 12 different seasons were singing birds. In one instance the
female of a pair arrived in the territory three days after the
male. Early in the morning the male bird sat high up in a leafless
tree singing. A low trrrr, which I have often heard both
male and female give as if in acknowledgment of its presence,
could be heard. There was a sudden flight to the ground. This was
followed by six or seven swift, circular flights of about 30 feet
in diameter, one bird in pursuit of the other. They both alighted
contentedly in the same shrub and began feeding among the fresh
leaves. This circular flight was accompanied by swift turnings to
bank with the curve. A few low notes were uttered during this
performance. Four days later the song of the male in this
territory was noticeably loud and long. Loud calls of excitement
were also heard, leading me to believe that the territory was well
established. Another observation of a similar performance was
made. The female stood on a low branch and fluffed her feathers
and raised her wings. The male chased her in half a dozen circular
flights. Between flights both birds fed among the fresh leaves,
often biting off pieces which fell to the ground. In this case the
female arrived six days after the male. He used the very highest
tree in the area as his song perch. This form of courtship was
observed even after the nest was built. Dr. A. A. Allen (1934)
states that he believes the act of copulation normally takes place
on the ground. On one occasion I observed what appeared to be
copulation but it took place in flight. The birds made several
circular flights after which one went to a small trickling stream
for a drink. Then the two met in the air. With a flutter of wings
and with wings spread, the male lowered himself to contact the
female. This took place about 8 feet above the ground, just over
the top of a bushy shrub. They continued to fly around after each
other.
Nesting.--The nest of the wood
thrush is much like that of the robin. Both contain a middle layer
of mud or plant material mixed with mud. The wood thrush's nest
can be distinguished from the robin's by the presence of dead
leaves and sometimes moss. Each wood thrush nest I examined was
lined with brown rootlets, whereas the robin's nests were lined
with dried grass.
All except two of 20 nests examined contained paper,
cellophane, white cloth, or some white material. One of the two
exceptions had long pieces of dried grass hanging from the bottom,
yet this was in a position within easy access of paper. The other
was away from habitations where such materials were not available.
These pieces of paper or rags used in the foundation of the nest
would seem to make it more conspicuous. Dr. A. A. Allen (1934)
suggests that perhaps enemies do not recognize such large affairs
as nests. My interpretation is that its use follows the theory of
concealing coloration in that it breaks the nest contour. The
bird's white underparts were sometimes used also. The female
fluffed her flank feathers so much that they and the under tail
coverts were visible, thus breaking the contour lines of the bird.
Also, the incubating bird, in holding her head high, shows the
white triangle of the chin and throat. It was also noted that when
something happened to frighten the incubating bird, she pressed
her body more deeply into the nest and held her head back farther,
pointing her bill upward. This made the white throat still more
conspicuous.
In all cases where rags, cellophane, and paper were used
they were white or transparent. In two instances in which it was
known that nests had been broken up or new ones were started,
pieces of colored paper, cellophane, and tinfoil were scattered
about to see if these would be used. In one case the second nest
was already built; in the other the birds moved beyond the area of
the scattered materials so the experiment came to naught. White
paper was used in both these second nests.
The nest is a firm, compact cup of grasses and weed stalks with
a middle layer of mud or leaf mold. In a few cases where the nest
was saddled on the branch, the nest was cemented to the branch
with mud. Every nest observed had dead leaves or leaf skeletons
tucked into the bottom. The nest is loosely lined with fine dark
rootlets. Inside, the nest measures 2 inches deep and 3 1/2 inches
wide.
The nest is usually fixed in a fork in saplings or undergrowth,
but some were found saddled on horizontal branches. Several nests
were found in shade trees near houses. Nests ranged from 6 to 50
feet from the ground. The average height of 15 nests was 10 feet.
Nesting materials varied considerably with the availability of
materials. Where paper was in abundance much was used. In some
nests more leaf skeletons were used than in others. One nest
contained many weed stalks because they were available. The
outside depths of nests varied greatly with their location. On a
horizontal branch the nest was shallow, to fill a crotch it was
deep.
I was not fortunate enough to observe the entire construction
of a nest. In one case building a blind frightened a pair from its
chosen site while a nest was under construction. In another
instance I found a deserted, partially built nest, so that the
progress could be traced. In one instance a pair was observed to
start the nest. Five days later it was finished and the first egg
was laid.
There seems to be little choice in selecting the kind of tree,
shrub, or vine used. The following list is a summary of 14 nests:
one nest each in basswood, juneberry, birch, locust, and a
grapevine; two nests each in maple, witch-hazel, and hawthorn; and
three nests in elms. Many references state that many kinds of
trees are used.
Territories used in 1936 and 1937 were used also in 1938. In
one case a pair built in the identical spot it had used the year
before, since I had removed the old nest after nesting was over.
I have no evidence of this species ever using the same nest a
second time or a second season.
The only reference to the fact that the wood thrush nests on
the ground is in the "Key for Identifying Bird's Nests,"
prepared by Helen Blair (1935). Mary H. Benson, a former student
at Alleghany State Park Nature Camp, has informed me that a wood
thrush's nest was found on the ground there and that Aretas A.
Saunders photographed it.
A wood thrush's nest, after being used by a family, is a
well-worn and sorry-looking abode. Pieces of loosened lining are
removed by the adults so that finally there is little left; bits
of the rim break off leaving it quite irregular; bits of feather
sheaths from the young are found on the bottom despite the
immaculate care given the nest by the adults.
The time of nesting is probably determined by the character of
the food of the young and also the concealment of the nesting site
and the young out of the nest. In Ithaca, N. Y., the nesting
season extends from May 12 until the end of July.
Nesting instincts are very strong in both the male and female
birds. The female often gives evidence of this by remaining on the
nest while a person walks up to it and stands within 3 feet of
her. An attempt was made to reach out and touch an incubating
female; she sat quietly until the hand was within a few inches of
her before she flew. The female, after banding, returned to the
nest within 15 minutes, while it took the male bird an hour to
quiet down after being excited. Several times the female returned
to the nest while the male bird was still uttering the quirt,
quirt call of alarm. The least movement in the vicinity of
the nest would cause the male to utter a low trrrr call.
Eggs.--The eggs of the wood thrush
are smooth, ovate in shape, plain in color. According to Ridgway's
"Color Standards" (1912), the color is "beryl
green" if the egg is dark; "pale sulphite green" to
"Nile blue" if it is light; or, in common parlance,
greenish blue much like those of the robin. The eggs of the wood
thrush are smaller than those of the robin and are more pointed
toward the small end.
[AUTHOR'S NOTE: The measurements of 50 eggs in the United
States National Museum average 25.4 by 18.6 millimeters; the eggs
showing the four extremes measure 28.5 by 19.3, 28.2 by 19.8,
and 22.4 by 16.5 millimeters.]
Authors give varying figures as to the number of eggs in a
clutch, varying from two to five. Data from my study show that in
no case was a clutch composed of five eggs. A fifth egg was laid
in one case after the removal of a punctured egg. Of 16 nests
observed in 1937, the average number of eggs per nest was three.
In 1938 the average number in 15 nests was four. Together they
average three.
In 1938 in 15 nests, 51 eggs were laid out of which 33 young
were produced from which 22 survived. This is a survival of 43
percent of the eggs laid, and 66 percent of the young hatched.
Evidence at hand does not show more than two clutches of eggs
for any pair of birds. In one case positive evidence was obtained
by marking birds that the second clutch was a second brood. This
will be discussed later. In many cases when the first nest was
broken up a second nest with a second clutch was found. In one
instance a pair built three nests, but in the second no eggs were
laid.
An egg is laid each day until the clutch is complete. In one
case I observed and timed the laying of eggs and found that they
were laid about 10:30 o'clock on two successive mornings.
Incubation.--Eggs were marked
so that the incubation period could be determined. It was found to
be 13 or 14 days. Incubation begins with the laying of either the
second or third egg. These conclusions are drawn from observations
on two closely watched nests of four eggs each. Eggs were marked.
The first two eggs in each case hatched in 14 days and the last
two in 13 days.
The brood spot occupies the region of the abdomen. It is deep
red in color and is devoid of all feathers. This was found only on
female birds and was used to identify the females when banding
them.
The eggs were turned by the female by clasping the egg between
the angle made by the bill, chin, and throat when the head was
pointed downward into the nest. With a raking motion she turned
the eggs.
Incubation is performed solely by the female wood thrush. In
order to prove this, a unique method of catching nesting birds was
employed. William Montagna had learned this in Italy. At the time
of this study he was assistant to Dr. G. M. Sutton, of the
Laboratory of Ornithology of Cornell University. He employed a
piece of orchard grass 2 1/2 feet long. The leaves were stripped
from it and a slip knot was tied at the end. The grass was moved
up to the bird on the nest without frightening her. It was slipped
over her head and tightened, and the nesting bird was captured.
These birds were then marked with colored feathers, as well as
aluminum bands, for identification purposes. Since no desertions
resulted, the method was considered successful. Subsequent visits
to the nests of birds marked in this fashion and observations on
other banded birds give evidence of the fact that only the female
incubates. Several birds were trapped with a drop trap as the
young were about to leave the nest. Only one bird of each pair had
a brood spot. Examination of the gonads of a bird, believed to be
the male of a pair with young in the nest, indicated that the bird
on the nest was the female. Brackbill (1943) also states that only
the female incubates. His study was made with marked birds.
I should like to describe the hatching of eggs by giving an
account of an all-day observation period beginning at 4:10 a.m. on
June 22, 1937, in Ithaca, N. Y. The female sat deeply huddled in
the nest. The male was singing soon after 4 a.m. From this time
until 7:15 a.m. the female would raise herself from the nest, back
off, and look in. Sometimes she would peck in the nest, then
settle on again with a rolling motion. She repeated this over a
period of four hours on the average of once every 15 minutes. At
9:15 a.m. her anxiety was relieved by the hatching of one of her
four eggs. Male birds of this species had not been observed to
feed the female on the nest, and so it was thought that perhaps
the male in this case was acting in anticipation of the coming
event when he arrived at the edge of the nest in the absence of
the female with a small green caterpillar dangling from his mouth.
He stood on the edge of the nest, looked in, ate the caterpillar,
then sang his full song. This was four hours before the hatching
of the first egg.
It took six minutes for the first egg to hatch. Four minutes
later the young was free from the shell and it called and opened
its mouth. The female fed it with a small insect she had picked up
in the nest. She waited 15 minutes after the hatching before she
carried away the shell. After leaving the blind, I found the shell
about 50 feet southeast of the nest. She took the small end first,
then six minutes later carried away the other piece. After she had
disposed of the first piece, the male brought food. The female
tried to give the food to the young but gave up and ate it
herself. Later the male came again with food. The female took it
from him and swallowed it.
The time required for the hatching of an egg varied greatly. In
one case it required 22 hours after the shell was pipped. Another
egg in the same nest required only 5 1/4 hours. In another
instance the shell was pipped one-half inch at 8 p.m., but the egg
did not hatch until 4:25 the next morning. The time probably
varies with the vitality of the young bird as well as with the
temperature of the egg.
The actual hatching is not a consistent procedure. The
movements of the young cause the shells to open differently, so
the young must use various means of freeing themselves from the
shell. In one case 10 minutes after the shell was completely cut
the left wing protruded from the opening. In another 10 minutes
the right wing and head were free. The feet were freed last. The
head of the bird lies in the large end of the egg. The head is
bent downward causing the egg tooth to cut the egg at the large
end at a distance of about one-fourth the length of the egg.
The egg tooth is a small whitish dot on the upper mandible near
the tip. It is still visible at the time when the young birds are
ready to leave the nest.
No one procedure was followed consistently in disposing of the
eggshell. In one instance the female carried the two halves
separately to a distance of 50 feet. Another time she carried away
the larger part but ate the smaller part. In one case she ate the
broken bits of the shell as it was being opened by the young.
| Progress of a typical wood-thrush nest: |
| Building nest, 5 days, May 28 to June 1. |
| Eggs laid, 4 days, June 2 to June 5. |
| Incubation, 13 days, June 3-4 to June 16-18. |
| Hatching, 2 days, June 16 to June 18. |
| Brooding, 12 days, June 16 to June 30. |
The number of young hatched from 43 wood-thrush eggs laid in
1937 was 27, or 63 percent. In 1938, of 51 eggs, 33 young were
hatched, or 64 percent. In 1938, of the 51 eggs laid, 43 percent
of the young survived to leave the nest.
In 1937, of the four nests which contained four eggs each, in
only one instance did all four young survive to leave the nest.
In 1938, of eight nests containing four eggs each, in two cases
all four young survived, and in one of these two. A cowbird
survived with the four young wood thrushes.
Young.--The first plumage of this
species is the natal down, which is light gray in color. Young
wood thrushes, at hatching, average 5.08 grams in weight. They are
approximately 46 millimeters in length; the tarsus averages 17
millimeters; the wing 9 millimeters; and the gape 9 millimeters.
On the second day the eye slit breaks through the skin but the
eyes are not open. The eyes open between the fifth and seventh
days (Brackbill, 1943). On the third day the first feathers, wing
primaries, and tail rectrices pierce the skin. The first wing
fluttering occurs between the ninth and twelfth days (Brackbill,
1943).
The female alone broods the young. Brackbill (1943) states that
there was no progressive daily decrease in brooding at either of
the nests he observed. During the cool hours of early morning the
female brooded oftener and for longer periods than during the
hotter part of the day. Brooding lasted throughout the nest life
of the young even on the day they left the nest.
Both females on the nest and young wood thrushes were observed
to sleep occasionally. The nesting adult would open her eyes quite
frequently only to close them again. The young slept both in the
nest and after they had left it. On one occasion a young bird that
had been out of the nest four days sat for 10 minutes on a small
branch with its feathers all fluffed out and its head under its
wing. A young bird in the nest was so relaxed during sleep that
its head hung down over the edge of the nest.
Young birds in the nest were marked with small pieces of
colored feathers glued to the tops of their heads so that
individual records of their activities might be kept. Both male
and female birds feed the young in the nest, each bird being fed
about every 20 minutes when the birds were seven and eight days
old. Young in the nest were fed mulberries and honeysuckle berries
as well as animal matter. The food call of nestlings is very weak.
It is a single chip in a high-pitched tone. Sometimes the adults
gave a squeaky call uttered with the mouth full of food, to get
the young to open their mouths. Once the male bird pecked the
female on the head to get her to move so he could feed the young.
At times the female flew away while the male fed the young, but at
other times she stood on the rim of the nest. Both adults disposed
of excreta either by swallowing it or by carrying the excretal sac
away. The adult that happened to be present at the time the sac
was expelled attended to the disposal.
Brackbill's (1943) calculations showed that the male made
two-thirds of the feedings while young were in the nest. The
feeding day corresponds roughly to the time between sunrise and
sunset. He also states that each bird was fed 47 times per day.
However, he found that birds of the second brood were fed every 39
minutes in comparison with l9 1/2 minutes for the first brood,
which resulted in but 24 feedings per bird per day, or half as
many as the first brood received.
The female birds observed by both Brackbill (1943) and myself
seemed to use some care in the type of food given the young. She
fed them caterpillars and small insects. If the male brought large
or hard-shelled or winged insects she ate the head, wings, and
other less easily digested parts before offering the remainder to
the young. The female was seen to divide food brought by the male
among several young instead of allowing one to have it all.
Brackbill states that young birds begin to forage for
themselves when 20 to 23 days old, although they may beg for food
from adults anywhere up to 32 days.
The adult male birds were usually in the close vicinity of the
nest to defend the young. The degree of their attentions varied
greatly with the individual bird. There is some indication that
the protective instinct is stronger early in the season. In one
case the male spent most of the time while the female was off the
nest perched above the nest. Other males perched in view of the
nest but sometimes as much as 20 feet away. The male at one nest
early in July was very inattentive. He did not guard the nest
closely, almost never helped in feeding the young.
During the two days before leaving the nest, the young birds
engaged in preening their feathers and occasionally beating their
wings rapidly. They would also stretch one leg or a wing its full
length and at times raise the whole body while standing on and
stretching both legs. A few times one was observed to shake the
whole body to fluff all the feathers. Sometimes one bird would
spend as many as five minutes exercising while the other two in
the nest remained quiet. When the one that had been exercising had
finished, it would settle down to rest while another would take up
the business of exercising. At times all the birds fluffed
feathers, preened, and stretched at the same time. In doing so
they crowded each other to the edge of the nest so far that a
sudden stretching of a wing was necessary to prevent the bird from
falling from the nest. Between periods of exercising the young
spent a considerable amount of time sleeping.
Few references were found in the literature to the number
of broods raised by the wood thrush in a season. Minot (1895)
indicates second broods near Boston, saying that first sets were
laid last week of May and "those of the second, if any, in
the early part of July." Harbaum (1921) observed a pair
through two nestings, but no evidence of the birds being marked is
given. The writer set out to find definite proof with marked birds
(since also found by Hervey Brackbill in Baltimore, Md., 1943). In
Ithaca, N. Y., young from a nest under observation were placed in
a drop trap just previous to the time for their departure from the
nest. First one adult was caught. This one was kept at a distance
in a collecting cage. The food calls of the young in the trap
attracted the other adult. When caught the adults were marked with
colored celluloid bands, as well as aluminum bands. A colored
chicken feather was glued to the tail feathers of each bird.
The first egg was laid in the first nest on May 19. The young
birds left the nest on June 15. On July 2 the second nest was
found. The same birds had mated and two eggs were in the nest.
These hatched on July 16 and 17. This second nest was located
about 10 feet from the first nest. If a pair of birds has to make
two or three trials before being successful in raising a brood,
the season is too far advanced for a second brood; if, however,
the first nest is successfully raised a second brood may follow.
The young birds unceremoniously leave the nest 12 or 13 days
after hatching. I observed no coaxing or "teaching" on
the part of the adults. The first in one case flew and alighted on
the ground about 20 feet south of the nest. The second, when
frightened, stood on the edge and flew, alighting on a small
branch near the trunk of a hemlock tree 20 feet above the ground.
The third bird in this nest remained quietly resting for half an
hour. Without being disturbed it stood on the edge of the nest and
flew to the ground alighting about 10 feet away.
The male bird seemed to defend the entire feeding territory
although he took charge of feeding certain of the young out of the
nest while the female fed certain others. This seems to need
further study. Brackbill (1943), in a case of three birds in a
brood, says that the male fed two out of the three in each of two
successive broods, while the female fed the third bird.
After leaving the nest the young stay in a limited territory
near the nest for several days. As their ability to fly increases
they move about. Birds were found in the vicinity of nests six to
nine days after they had left. They were still being fed by the
adults. The adults would return to the spot where the young was
fed last. The food getting was usually confined to an area close
to the young. The young bird would often lift and flutter its
wings rapidly when approached by the parent with food, at the same
time uttering rapid, squeaky calls.
Plumages.--The newly hatched wood
thrush is clothed in natal down. The juvenal feathers are a
continuation of this down, which is carried out on the tip of the
new feathers and is finally rubbed off. The down is still present
when the young leave the nest. The loss of the down is the
postnatal molt. The juvenal plumage is the first complete plumage
of the bird following the natal down and is acquired by the growth
of new feathers. Sheaths are short and are lost quickly, as a bird
when ready to leave the nest has no sheaths on the short body
feathers. Therefore, when sheaths are found approximately six
weeks later, they are known to be those of new feathers. Then, at
six weeks the juvenal plumage is lost by an incomplete postjuvenal
molt in which the body feathers are lost but not the flight
feathers, neither in wings nor tail. This molt brings the bird
into its first winter plumage.
The first nuptial plumage is supposedly acquired by abrasion or
feather wear accomplished by casting the points of the feathers.
This takes place on the wintering grounds before spring migration.
The postnuptial molt is complete, both body and flight feathers
being lost. Specimens were found in molt at the end of July. These
birds were practically "bob-tailed." At this time the
birds are secretive in habits, of necessity.
Wetmore (1936) states that a female weighing 60.4 grams had
2,075 feathers, which weighed 3.2 grams.
Brackbill (1943) banded a partially albino female wood thrush.
It had a white feather in the crown, some white feathers among the
upper tail coverts, and four white rectrices. The eyes were
normal. No sign of the inheritance of this character could be
noted in any of the two broods of three young.
Food.--Thrushes are insectivorous but
are fond of fruit. The U. S. Fish and Wildlife Service supplied
the following data on the food of this species, based on 179
stomachs examined. These birds were taken from 19 States, 5 from
Ontario, Canada, and 19 from the District of Columbia. They were
unequally distributed over nine months of the year, the months of
May and July yielding more specimens.
In the 179 examinations, 62.25 percent of the material
consisted of animal matter and 37.75 percent vegetable matter. Of
the latter, 3.49 percent was cultivated fruit and 31.2 percent
wild fruit. In general, this bird is beneficial, although 2.17
percent of its food is composed of useful Coleoptera, 8.38 percent
of Arachnida, and 3.49 percent of cultivated fruit, making a total
of 14.04 percent of food substances useful to man. This percentage
is canceled by its consumption of the following predators:
Orthoptera, 2.1 percent; Rhynchophora, 2.16 percent; and
Lepidoptera, 11.29 percent, making a total of 15.55 percent of
food substances in the harmful class.
During my observations the following foods were fed to young
birds: Several species of moths, ants, spiders, caterpillars,
mulberries, honeysuckle berries, earthworms, and cankerworms.
Economically, then, the wood thrush is to be encouraged, for
its food habits prove that it is a valuable aid in the destruction
of many injurious insects and but few beneficial ones.
It was observed that soon after their arrival the birds fed
from the foliage of the newly leaved trees. In their feeding they
sometimes broke off pieces of leaves which fell to the ground.
Later most of the feeding was done on the ground. Their presence
in an area can often be detected by noticing them turning over
leaves with the bill. A letter from D. J. Nicholson to A. H.
Howell contains an interesting incident in which the writer saw a
wood thrush eating pokeberries by springing up18 inches and
plucking off a berry. He also took a picture of these birds eating
fallen gallberries.
Behavior.--When alarmed, wood
thrushes, both adults and young, raise and lower the feathers of
the head, giving the appearance of a crest. The young have been
observed to do this only just previous to the time for leaving the
nest, or after the fear instinct has been developed.
While incubating and brooding, when the temperature was high,
the female lifted her wings from her sides and raised the feathers
of her back and sides to allow air to circulate beneath them. She
and the young in the nest often sat with mouths open when it was
hottest.
The wood thrushes' reactions to storm and rain were noted by
Brackbill (1943) and by the writer. Brackbill observed a female in
a heavy downpour. She sat closely, holding her head at an angle of
60o, presumably to compress the
feathers at the nape of the neck. During a late afternoon storm it
became very dark and the male bird I was watching, who had been
guarding the nest in the absence of the female, settled on the
nest and covered the young. It rained and the wind blew quite
hard. During a very heavy wind, Brackbill watched an incubating
female. At times the eggs seemed perilously near falling from the
nest, as it was tilted by the wind, but the female remained calm.
A few times she almost lost her balance.
[AUTHOR'S NOTE: When living in our towns and cities, the wood
thrush loses much of its natural shyness and timidity. We often
see it leave the shelter of the shrubbery or leafy thickets in the
more secluded borders of our grounds and come out onto the lawn in
search of food, almost as fearless as a robin. It may even visit
the bird bath or take a shower bath under the automatic lawn
sprinkler, provided that we are careful not to frighten it by too
close an approach. It seems to be more trustful of its human
neighbors than does its shy relative in the woodlands.]
Voice.--Saunders says: "The
song of the wood thrush is long continued, made up of a number of
different phrases, sung in varied order, with rather long pauses
between the phrases. It sounds like eeohlay----ayolee----ahleelee----ayleahlolah----ilolilee,
etc." Elsewhere (1924) he writes: "Each phrase may have
three parts, an introduction of two or three short notes, usually
low in pitch and not especially musical; a central phrase of two
to five notes, most commonly three, loud, clear, flute-like and
extremely musical; and a termination of three or four notes,
usually high-pitched, not so loud, and generally the least musical
part of the song. Phrases may be sung either with or without
either introduction, termination or both, and sometimes,
especially late in the season, birds indulge the habit of singing
only introductions and terminations, leaving out the beautiful
central phrases." Saunders made records of 115 wood thrush
songs, which showed the pitch to range from D'' to D'''', two
complete octaves. The average bird has a range of a tone or two
over an octave.
The song of the wood thrush early in the season is more
elaborate, performed with more vigor, and is of longer duration
than songs later in the season.
The calls fell into three classifications discussed here in
order of the degree of feeling seemingly expressed by them. When
slightly disturbed, or uneasy, apparently to indicate his or her
presence, both male and female utter a sound that can be expressed
by trrrrrr, trrrr, a sort of rattle or trill. The other
bird would then often respond with the same call. If they became
alarmed they used the pit, pit, pit call. When greatly
alarmed, as when danger threatened nest or young, the call changed
to quirt, quirt, quirt, quirt, usually accompanied by swift
zooming flights at the intruding person, bird, or object. During
this defensive demonstration the bill was snapped and the birds
came within a few inches of the object of their fury. This
happened once upon the erection of a blind.
Another sound made by both male and female was a squeaky
whistle. During the nesting period both male and female were heard
to give this clear whistle upon several occasions. This was used
by either adult upon arrival at the nest with food, especially
when the young did not open their mouths to receive it. Sometimes
it was necessary for an adult to repeat this at least four times.
It can be described by saying that it seemed to have been produced
by inhaling with the bill almost closed. It was often given when
the bill was filled with food. The female sometimes gave this
sound while she was on the nest. It was also used by the male when
he sat at some distance from the nest or when he arrived with food
and the female did not leave the nest so that he could feed the
young.
Brackbill (1943) describes a "rudimentary or vestigial
song"--an explosive one used by the female in defense of
territory.
The young birds uttered a faint chip, which was the food
call. This was not loud enough to be heard at any distance but
could be heard easily from the blind. My first record of such a
call was made, as mentioned before, four minutes after the young
was free from the shell. This call also serves to indicate the
location of the birds after they have left the nest. Brackbill
(1943) says that the juveniles began using a rudimentary form of
the adults' rattle or trill, which consisted of three or four
notes, at the age of 21 days. Also when chased a young bird bursts
into a series of calls similar to the adult call I have described
as pit, pit.
Early in the season wood thrushes perched in the tops of the
highest trees in their territories to sing their loudest, most
complete, and most varied songs of the season. A week later
perches were about 15 feet above the ground. Often they chose
short, dead branches of hemlocks. Others were known to sing from
the ground, from large logs, in the nest tree, or even from the
edge of the nest in the absence of the female.
From my observations, wood thrushes begin their morning songs
with the break of day, singing at the end of June at 3:45 a.m. in
Ithaca, N. Y. At this time it is still quite dark and feeding has
not yet begun. This singing continues both through the periods of
incubation and brooding. Evening song usually ceases at dark, or
about 8:00 p.m. in June in Ithaca. Wright (1912) made a study of
morning awakening and evening songs of birds in the White
Mountains of New Hampshire in which he recorded the average of
early wood thrush songs as 3:26 a.m. The earliest sunrise during
the study was 4:02, and so the wood thrushes sang about half an
hour before sunrise.
Song on the breeding grounds begins with the arrival of the
first birds; so it is believed that the males do not wait until
the females arrive before the song period begins. Males arrive and
sing to denote the possession of their territory. There was song
in the evening only, after the young had left the nest.
On one occasion Brackbill heard a wood thrush sing a song of
good quality while on the wing and not in defense of territory.
Forbush (1929) describes the calls and song as follows:
"Notes, a liquid quirt, a low tut tut, a sharp pit
pit or pip pip and a shrill tsee tsee. Song, a
pure, clear, sweet, expressive, liquid refrain, often with a
bell-like ending; usually composed of a series of triplets, each
beginning with a high note, then a low one, then a trill, often
highest of all, but the different phrases varying in pitch. It is
calm, unhurried, peaceful, and unequaled in both power and beauty
by any other woodland songster of New England."
Saunders (1921a) claims that individual male wood thrushes have
characteristic songs by which they can be identified. John
Burroughs (1880) also makes this statement. Saunders says that a
count of pairs merely by singing males is not reliable, but such a
count would be possible if individual songs were studied.
Charles W. Townsend (1924) and Francis H. Allen, quoted by him,
state that they heard catbirds mimic the song of the wood thrush.
The white-eyed vireo, according to Brand, is an imitator of this
bird, and Forbush (1929) reports that it has been known to imitate
the wood thrush.
About the middle of October 1927, at 2 a.m. on a moonlight
night, a large flock of birds alighted in tops of street basswoods
in residential Washington, D. C. (Hazen, 1928). Immediately at
least 10 wood thrushes burst into full song. They sang
continuously for 20 minutes, then one lone bird sang until the
flock disappeared at 2:45 a.m. The thrushes were accompanied by
small tree-top birds, either vireos or kinglets.
The latest songs of the wood thrush in the autumn were recorded
on July 28 and August 10 at Ithaca, N. Y. Brackbill (1943) records
August 2 in Baltimore, Md. Saunders gives July 29 as his average
fall song date. His latest dates are August 8, 1928, and September
7, 1941. As a rule, then, the song period closes about the end of
July, and little is seen or heard from the birds from then on.
During the postnuptial molt birds were located by listening for
the calls of excitement, but no songs were heard.
Field marks.--The members of
the genus Hylocichla have more or less spotting on the
under parts and the young are spotted above and below in the
juvenal plumage. The distinguishing characteristics that separate
this species, mustelina, from the others of the genus are
its larger size (over 8 inches in length) and greater sturdiness.
Its upper parts are bright cinnamon-brown, being brightest on the
head and changing gradually to olive on the upper tail coverts and
tail. (The hermit thrush has the cinnamon-brown most pronounced on
the tail.) The under parts are white, thickly marked with large
rounded dark brown spots, except on the throat and middle of the
belly. This species is more strongly marked than others of the
genus; the spots are larger, more distinct, more numerous, and
more generally dispersed. The spots extend well down on the
flanks, more so than on any of the other thrushes. In
distinguishing this bird from confusing species other than
thrushes, we may eliminate the brown thrasher by the fact that it
is longer-tailed and is streaked below rather than spotted. The
large dark eye of the thrush is to be compared with the yellow eye
of the thrasher (Forbush, 1929). The fox sparrow is
reddish-tailed, under parts streaked, not spotted, and the bill is
thick, conical, and sparrowlike rather than slender like that of
the thrush.
Enemies.--Cats are responsible for
the destruction of some wood thrushes. "Causes of death"
listed on banding returns in the files of the United States Fish
and Wildlife Service show that on 74 returns 8 percent of the
deaths were due to cats.
In 1938 three nests were deserted because of the destruction of
the entire clutch of eggs. In each case a few very tiny bits of
the shells were found in the nests. Those acquainted with the
predators of the region offered the suggestion that the red
squirrel may have been guilty.
Approximately one-fifth of the nests studied were parasitized
by the cowbird. This social parasitism decreases the numerical
strength of the species by causing desertion in some cases. A few
instances will be cited. In a nest containing one cowbird egg and
three wood-thrush eggs, the thrush eggs disappeared, one each day,
until only the cowbird egg was left. The nest was deserted after
the last egg disappeared. In another case the writer removed three
cowbird eggs from one nest. In one nest containing a day-old
cowbird and one thrush egg, the thrush egg did not hatch. In
contrast, however, a nest contained four wood-thrush eggs and one
cowbird egg, all of which hatched and all the young survived to
leave the nest.
Friedmann (1929) in his book on the cowbird gives interesting
information on its relation to the wood thrush. The wood thrush is
larger than the cowbird yet is frequently parasitized and is also
seen caring for young cowbirds. Often the cowbird is the only
survivor in a thrush nest. Records of such parasitism come from
New England, Connecticut, New York, Pennsylvania, and Maryland,
Ohio, and Indiana.
Perry (1908) describes a wood thrush nest in Illinois in which
five cowbird eggs were laid. These were laid by at least two
cowbirds, since two were deposited on the same day. Despite this,
one young wood thrush lived to leave the nest successfully.
In one instance I recorded the feeding times of a young cowbird
which was in a nest with one wood thrush. There are many
uncontrolled factors that would discount any conclusions drawn,
but in this case the feedings were of the same number, averaging
about one every 15 minutes.
Wood thrushes react to cowbird eggs in several ways. There was
some evidence that the wood thrush tried to imbed the intruder's
eggs. Friedmann (1929) said in the majority of cases the eggs and
young were tolerated, and that Lynds Jones knew a case in which
the wood thrush tried to throw the cowbird egg out.
Wood thrushes seem to be fairly free from external parasites,
as none were found on the many birds handled during the study made
by the author. There were indications at times that the adults
picked them from the nest; one time, after picking in the nest,
the adult put her bill into the mouth of a young bird seeming to
feed it. Peters (1936) lists two parasites found on this species,
one a louse (Myrsidea incerta Kellogg), on a specimen from
New York, and a tick (Haemaphysalis leporis-palustris
Packard), on a specimen from North Carolina.
A study of the Federal Government's records of bird-banding
shows that, up to May1936, the oldest banded wood thrush was six
years old. From my own records, I had a bird three years old,
which nested in the same vicinity each of the three years.
Fall.--Records of the United States
Fish and Wildlife Service were studied to make this summary of
fall migration. In the Atlantic flyway in September, wood thrushes
are still in their summer range, being found as far north as they
were during the summer months, although there is no way of telling
in what numbers they are present. The autumn migration begins in
October. The northernmost records for October are one for Maine,
one for central Vermont, and one for New Haven, Conn. They are
still numerous in New York, Pennsylvania, New Jersey, and the
District of Columbia. In November there are about a dozen records
of birds in the United States, so that by this time most birds
have left our country. The first actual record of a bird south of
the United States is one for Almirante, Panama, on October 30.
In the Mississippi flyway in September, wood thrushes are
still as far north as they were during the summer, being found in
Ontario, but October records show a southward movement. The last
fall record is at Ozark Beach, Mo., on October 27.
There were only six records on file of fall dates in the
Western flyway. In September a record was made in Sioux Falls, S.
Dak. The last fall record was made at Independence, Kans., near
the end of October.
In comparing these data we find that wood thrushes remain
longest in the United States in the Atlantic Coast States.
There is an interesting note by Weston (1935) about the fall
migration of wood thrushes at Pensacola, Fla.: "A heavy
flight of wood thrushes filled the swamps with birds on October
13." The latest date given by Howell (1932) for Florida is
October 14.
In Ithaca, N. Y., the latest fall record is September 18.
A. A. Allen (1934) and Lincoln (1935) state that the thrushes
migrate at night because light is less intense, they can then
better avoid their enemies, and they can take care of feeding
during the daytime.
Fall migration, then, can be described as irregular since some
birds are found in the United States (Florida) every month of the
year, but most have left the country by the end of October.
A study of migration records leads me to conclude that there is
no definite route of migration either in spring or fall. This is
contrary to the statement that thrushes prefer the Mississippi
Valley flyway.
Winter.--Most wood thrushes have
left the United States by the end of October, but there are a few
records for November some of which are quite far north: New
Hampshire, New York, New Jersey, and Pennsylvania.. The scarcity
of records, however, would indicate that these are stragglers and
that by November most of the birds have left the United States.
The United States Fish and Wildlife Service had but a dozen
records for November at the time this study was made, and of
those, four were from places south of the United States: one for
Nicaragua, two for Costa Rica, and one for Panama. In December
there are records from New Jersey, South Carolina, Alabama, and
Florida, in the United States, and two for places south of our
country, one from Costa Rica and one from Barro Colorado Island,
Panama. The January records are from Georgia, Florida, and Mexico,
only one record in each case. These were the only records in the
files for that month. The February records consist of four from
Florida, with others from Mexico, Guatemala, Honduras, and Costa
Rica.
Roberts (1932) summarizes, saying: "Winters in southern
Mexico and Central America and occasionally in Florida. Casual in
migration in the Bahamas, Cuba, and Jamaica; accidental in
Colorado and Bermuda."
In checking the Christmas bird-census records in Bird-Lore,
I found two records of observations of the wood thrush. At Cape
May, N. J., 1934, one was seen by McDonald and others. Another
record was from Paris, Tenn., where three were seen in 1933.
Howell (1932) lists four records of wintering individuals in
Florida.
O. Salvin (1888), in writing of the birds of the islands off
the coast of Yucatan, says: "A migratory species from the
north, and common in Cozumel Island. It has not been noticed in
Northern Yucatan, but it occurs in Cuba, though rarely. It is
abundant in the winter months in Southern Mexico and Eastern
Guatemala, the southern limit of its range being Northern
Honduras."
Alexander F. Skutch, an American ornithologist in Costa Rica,
writes me that he observed a wood thrush on Barro Colorado Island,
in the Canal Zone, in March1935. He says it "was singing when
I came upon him. Although it is stated by Carriker and others that
the North American birds which winter in Central America are
'almost invariably as silent as so many shadows', this is quite
untrue. Many of the song birds which pass the winter here begin to
sing a short time before their departure for the north."
A note from Mr. Skutch to A. C. Bent summarizes his Central
American observations of the wood thrush: "The wood thrush
winters in Central America throughout the length of the Caribbean
lowlands; but I have found it far from abundant in Guatemala and
Honduras, and exceedingly rare in Costa Rica and Panama. During
the winter months it does not form flocks, but leads a solitary
life, in the undergrowth of the forest, in low moist thickets, or
even in banana plantations. On March 21, 1935, I heard a wood
thrush sing in the undergrowth of the forest on Barro Colorado
Island, Canal Zone. His song was subdued but perfectly distinct,
and beautiful as always. The single thrush was in company with
antbirds of several kinds. My only records that suggest the time
of arrival and departure of this migrant are: Tela, Honduras,
October 1, 1930; near Los Amates, Guatemala, April 4, 1932; and
Barro Colorado Island, March 21, 1935."
Wood Thrush*
Hylocichla mustelina
Contributed by Florence
Grow Weaver
*Original Source: Bent,
Arthur Cleveland. 1949. Smithsonian Institution United
States National Museum Bulletin 196: 101-123. United States
Government Printing Office
Return
to FAMILIAR BIRDS Home Page
Return to
beginning of document
|
