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
*Original Source: Bent, Arthur Cleveland. 1949. Smithsonian Institution United States National Museum Bulletin 196: 101-123]. United States Government Printing Office