Contributed by Alfred Otto Gross
[Published in 1948: Smithsonian Institution United States National Museum Bulletin 195: 113-141]
*** One of the earliest recollections I have of birds is a pair of energetic little house wrens that built in a rustic box placed inside an open porch of our Illinois home. These little brown birds (unknown by name to me at that time) had an intriguing fascination, with their constant going and coming with flitting upcocked tails, their innumerable visits to the nest with food to satisfy their clamoring young, their chattering vibrant songs, and their saucy scoldings when I ventured too near; all those early experiences have left indelible and pleasurable memories. For similar reasons the house wren has gained countless human friends who cherish the presence of these birds as tenants about their homes.
Unfortunately, individual house wrens, especially those inhabiting populated areas, have displayed, too much aggression for Lebensraum in their relations to other birds. This Nazi trait has brought them into disfavor by persons who now hold a strong prejudice against this attractive and useful bird.
The house wren because of its depredations on the nests, eggs, and young of other birds has been hailed into court where notable witnesses both for and against his character have taken the stand. The controversy raged during the twenties as evidenced by the numerous articles and communications published in the ornithological journals. Sherman (1925) in a spirited article, "Down with the House Wren Boxes," took a venomous stand against the wren. She reviews at length the statements made by numerous observers, of the destructive tendencies of the house wren, especially toward those species that come into direct competition with it, through their nesting in the same environment. Miss Sherman's paper stimulated the writing of many of the articles for and against the wren that followed.
Chapman (1925) in an editorial on the wren controversy stated in part as follows:
The day that I returned from Florida I found the House Wren here to greet me. . . . The bubbling music which springs so uncontrollably from his quivering throat is too characteristic a part of the season's chorus to be spared. The box which has been hanging so patiently on my grape arbor would be but a sad reminder of past joys if it should not again be animated by his bustling little body.
Tried in a court of men and he no doubt would be convicted of the charges made against him; but a court of Wrens would dismiss the case and commend the culprit. Purely as a matter of justice which verdict should we take? Should we judge Wrens by their standards or by ours? That we may insist that they conform to our standards is quite a different matter. . . .
The so-called nature-lover who takes his own standards, personal likes and dislikes afield with him, is apt to find quite as much to condemn in animal as in human life. Nature attracts us primarily because she is natural. It is the wild not the tame animal which appeals to us; and we want it to exhibit the traits which have won for it a place among competitors. . . .
The House Wren has become abundant with our help and through the exercise of the instincts which have made it a successful species. But is there any reason why we should call him a criminal? As a matter of fact we are the guilty ones. Inspired by the best motives and encouraged by those in authority, in an excess of zeal we have embarked on a campaign in the behalf of the hole-nesting birds without perhaps stopping to think just where it will lead us.
McAtee (1926b) reviewed the evidence from the standpoint of an economic ornithologist in his article "Judgment on the House Wren." He writes in part as follows:
Recently the relations of the House Wren to other birds have been fully discussed in our ornithological journals. The Wren has had its supporters as well as defamers, but few on either side have taken a justicial view of the controversy. The evidence that House Wrens sometimes destroy the eggs and otherwise interfere with the nesting of other birds is indisputable, but it is not so positively realized that this is only one of the factors we must take into consideration in forming a judgment (in the technical sense of the term) on the economic value of the species.
Many birds are so free from special vices or virtues that their economic status is decided upon the basis of their food habits alone. Were this true of the House Wren, the species would receive a very high appraisal, for it is almost exclusively insectivorous, and that, too, in chiefly commendable directions. . . . The House Wren is as worthy of approbation as any of our birds on the score of its food habits. It has a better rank in this respect than most of the species whose eggs it occasionally destroys. Egg and nest destruction by the Wren is of local, not general, occurrence and the remedy should be local. It is simple to eliminate bird houses that only Wrens can use, a measure to be applied in places where serious depredations have been noted, or to close temporarily, or reduce in number, houses that have proved bases for sporadic marauding. Most problems in economic ornithology resolve themselves into local irregularities of bird behavior, and the wisest treatment in almost every case proves to be that adapted both in kind and degree to local needs.
The relations of the house wren to other birds make him a much more interesting, even though it be less desirable, personality. His aggressions toward other birds have not been recently acquired but constitute an old and well-established trait. His behavior is evidence of his superior intelligence in the battle of the survival of the fittest. He is activated to secure and dominate a definite area during the reproductive season for the sake of his own preservation. For this reason this small enterprising midget making his way in the world, often against superior odds, deserves our respect rather than our condemnation. If man upsets the balance of nature by his interference, for example by erecting too many nesting boxes, then man alone is to blame for the conditions which prevail in certain localities.
Spring.--The first arrivals of the house wren make their appearance along the southern limits of the breeding range during the latter part of March, but it is not until the middle of April that they become common. Certain individuals remain on the southernmost wintering grounds until the second week of April. In Florida a series of 8 years of records of birds last seen in the spring range from April 12 to April 22, an average date of April 17. The first house wrens arrive in New England and a corresponding latitude in the Midwest during the last week of April or early in May, but it is not until the middle of the month that the nesting activities are in full swing. At Hillcrest, Ohio, according to Kendeigh (1941), who made observations on the time for beginning of the nesting activities of 186 males and 165 females, "The median date for all the males to begin nesting activities is May 11, although the median date for the first male activity is May 1, and for the latest male to begin activity. . .is June 22. Females average later, the corresponding three dates being May 20, May 11, and July1." Kendeigh continues:
Although first-year birds may be among the first to arrive in late April and early May, adults of two or more years of age make up a far greater percentage of the migratory population at this time than they do later in the season. Females arrive about 9 days later than the males.
Adult males that have previously nested almost invariably return to the same territory that they formerly occupied, or they establish a new territory adjacent to it. The return of adult females to their former nesting areas is almost as regular.
With young birds hatched the preceding seasons, there is a marked tendency to scatter in all directions, although they occur in greatest relative numbers in the vicinity where they were hatched.
Territory.--As soon as the male appears on the breeding ground his arrival is announced by the territory song. The male isolates himself and establishes himself in a definite area. Territory is important as a means by which birds become paired and mated and an insurance for adequate nesting sites and food supply. According to Kendeigh (1941)--
The process of courtship and mating can scarcely be separated in the house wren from the phenomena of territory, as they are so vitally interwoven and intrinsically related.
Territory is established and defended chiefly by song. . . . The "territory song" of the house wren is but little different from the "nesting song," and both songs announce to other birds that the territory is occupied. [The territory song is also an advertisement of the male's presence to females, and of inducement to the female to enter a particular male's territory in preference to the territory of some other male.]
The presence of a female is a distinct incentive to song. The male will give his territory song over and over again, day after day, in a purely mechanical manner until a female comes into view. Not really until then does he show emotional excitement. The song is given more energetically, the mating song is interspersed and males from adjoining territory may tune in. Competition between two males in adjoining territories becomes most vigorous when an unattached female enters the area. . . . The male whose song is most stimulating to her ears would seem to have the advantage.
In addition to song, territories are also defended by the wren's assuming threatening postures sometimes accompanied with scolding, chasing, or physical combat.
In the establishment of nest sites, house wrens may destroy the nests, eggs, or young of the same or different species, or even the adult birds. Although there is considerable individual variation in this aggressive behavior, it tends to be most intense during years when the total house wren population on the area is highest. . . .
Territories in the Hillcrest area average 1.0 acre. . .in size. . . . The size of the territory varies inversely with the size of the house wren population and does not exert a limiting influence on the total numbers of the species in the area until it approaches the minimum compressible limit. The adult birds restrict their intensive daily activity to limited parts of the territory but eventually cover the entire area. . . .
The successful mating of two birds of opposite sex appears to depend on their physiological and psychological readiness, their ability to stimulate each other sexually, the location and character of the territory [and] nest site together with nest foundation begun by the male, and finally their freedom from other activities.
Territory is maintained throughout each breeding period and breeding season, although there may be some decrease in activity as nesting progresses. This continuance of territory may be correlated with the tendency toward polygamy manifest in the male, with the use of the same territory for later matings, and it may also involve the need for a constant and readily available source of food and for freedom from annoying intruders. Primarily, however, the territorial behavior is most closely linked with the acquiring of a first mate. There is no evidence that territory is maintained at any other than the breeding season of the year.
Courtship.--With the arrival of the female an ardent courtship begins. They have an extensive repertoire of songs and call notes, which are used for various occasions and for purposes of intercommunication. Both males and females have a habit of quivering their wings when excited, which is most pronounced during the mating process but is evident also when the birds are disturbed or scolding. The position of the male's tale is also a good indicator of the degree of his excitement. During ordinary singing it is kept lowered, but when his courtship song is intensified, or at times when he is scolding, the tail is tilted upward. During copulation it is vertical or tilted forward at an acute angle.
Much excitement is manifested during the inspection of available nesting sites, some of which have already been selected and partially filled with sticks by the male. The female has opinions of her own resulting in violent domestic controversies that intersperse their passionate courtship antics. The female may refuse the nest proffered by the male; sometimes she may accept the nesting box but, disapproving of the nesting material or the way it was arranged by the male, proceeds to throw it out stick by stick. Both birds do their part in the building of the final nest, but the male spends more time singing and guarding the nesting territory.
After the female is busily engaged with her incubation duties the activities of the male are less important since all he does is to sing rather mechanically. Occasionally he spends his time carrying sticks into some nearby box in the pretense of building a new nest, and while doing so he sings his courtship song. In fact, the building of the extra nest has been thought to be one of the manifestations of his peculiar courtship. While so employed he often acquires a second mate while the first is still busy with household duties.
Nesting.--The house wren stands out preeminently as one of the most eccentric of our birds in the choice of its nesting site. In fact, its choice of nesting place exhibits such extreme variation that it is difficult to select one that can be considered typical.
The primitive environment of the house wren was the woodlands and its nesting site the natural cavity of some tree or stump. The nest is seldom exposed, but generally the requirements of the wren demand an enclosure that conceals the nest on all sides except the point of entrance. These birds have readily adapted themselves to the environment of man reaching a state of semi-domesticity. They have availed themselves of houses constructed for their special use or lacking these have built their nests in various contraptions incidentally provided either inside or outside of buildings. They are not particular and are just as apt to accept an old rusty can in a garbage heap as they are a neatly painted house set in the midst of a beautiful flower garden.
Innumerable curious nesting places have been reported, a few of which will serve to illustrate their infinite variety. At a sanctuary located on Wallops Island, Va., 24 empty cow skulls found bleaching on the island were hung up or lodged in the trees and shrubbery. Almost immediately 23 of the gruesome skulls were occupied by house wrens, who were quick to accept these unusual nesting boxes (Forbush, 1916). There are several instances where house wrens have built their nests inside the large paper nests of hornets or wasps that were attached to private or public buildings. Before adding nesting materials the interior of the insect nests were excavated by the industrious birds. This relationship between wrens and wasps was reversed in one instance, as illustrated by a photograph taken by R. E. Hart (1941) on the campus of Keuka College, New York. A wren house was taken over by a swarm of wasps and was completely covered except for a small part of the roof, with successive layers of paper laid down by the insects.
It is not uncommon for the wren to make use of the nests of other birds. At Loring, Va., a pair of wrens built in a deserted barn swallow's nest. At Laanna, Pike County, Pa., Burleigh (1927) writes of a nest containing seven eggs which was in a robin's nest on a ledge above a pillar of a porch. Here the cavity had been deepened and a few twigs and feathers added, but these were not noticeable a short distance away. He found another nest in a barn swallow's nest lodged against a beam in the roof of a barn. Here again the cavity had been deepened and a few twigs and feathers added. Both nests were new and apparently had been appropriated from the rightful owners. Angus (1934) reports finding five young wrens in a phoebe's nest under a bridge, and in this case no nesting material had been added by the wrens. Wilbur F. Smith (1911a) relates a strange partnership in which wrens and English sparrows built a nest in a bird house, the sparrows starting first. Both the sparrow and wren laid eggs that were incubated by the English sparrow. Though wrens are ordinarily antagonistic toward bluebirds and tree swallows, they have been known to occupy different compartments of the same martin house and exist in apparent harmony.
Not only do wrens occupy nests of other birds built in boxes or natural cavities or those in the protection of buildings but also they have appropriated nests built in open situations. Schwab (1899) writes of a pair of wrens that occupied the deserted nest of a Baltimore oriole hung 20 feet from the ground in one of the outermost branches of a large sugar maple tree. Two other cases of wrens occupying oriole nests have come to my attention; hence the above case is not unique. At Bay of Erie, Pa., a pair of wrens departed greatly from their nesting environment when they selected a kingfisher's nesting hole in a sand bank. This nest contained young when discovered (Sennett, 1889). Still another unusual nesting site in relation to other birds was that of a pair of wrens which built in the deeper interstices of an osprey's nest located on Plum Island, N.Y. (C. S. Allen, 1892).
Other interesting nesting sites of the house wren have been in a fish creel or watering pot hung on the side of a shed or fence, rusty tin cans in garbage piles, old threshing machines and other farm machinery, in tin cans, teapots, and flowerpots left on shelves of sheds, in a soap dish, in old boots and shoes, and even in a bag of feathers. Outdoors they have been known to nest in the nozzle or main part of pumps, in the hat or pockets of a scarecrow, in an iron pipe railing, in a weather vane, in holes in a brick wall or building, and in a coat hung up at a camp site. One pair of wrens built their nest on the rear axle of an automobile which was used daily. When the car was driven the wrens went along. Even under these most unusual circumstances the eggs were successfully hatched (Northcutt, 1937).
The individual wrens have one trait in common in that these energetic creatures strive to fill the container they select with nesting material. Regardless of its size it is usually well filled except for a narrow passageway leading to the comparatively small nesting cavity that contains the eggs or young. This trait is probably one that has developed through the protection the birds derive by keeping out certain intruders. This fact is often considered in the construction of wren nesting boxes by cutting an entrance large enough to admit the tiny body of the wren but too small to admit the passage of competitors the size of an English sparrow or a starling.
The bulk of a house wren's nest is generally composed of relatively long and coarse twigs and sticks and grass. According to Godard (1915) if the wrens are given a choice of dry and green sticks they select the dry dead sticks and reject the green ones. The nesting cavity is usually lined with finer and softer materials such as feathers, hair, wool, spider cocoons, and catkins.
McAtee (1940a) analyzed the materials in 33 complete or partial nests found at the Bureau of Plant Industry Experiment Station located near Glen Dale, Md. His report is as follows:
Foundations include (in the number of nests indicated): twigs (33), feathers (16), chestnut spikes (13), wool (12), leaves (7), cord (6), and weed stalks (5). Materials used in fewer instances were: rootlets, red-cedar bark, cotton, grass, chestnut shell, paper, a large fragment of snail shell, exoskeletons of milliped and sowbug, and a spider cocoon. The twigs were characteristically coarse and included some up to 8 inches in length and a few that were branched. Rose twigs with plentiful thorns were frequently employed, and in a few cases callow young were raised in such nests with little or no cushioning to protect them from the spines. The twig bases of nests were often from 4 to 6 inches deep. Flecks of wool and cotton were scattered through the twig bases to no conceivable purpose. The lining of the 33 nests included grass in 19 cases, hair, chiefly horsehair, in 16, feathers in 13, and rootlets in six. Other items were red-cedar bark, chestnut spikes, weed stalks, and grass. The material in one nest, loosened up in the process of analysis, filled a 2-gallon bucket.
The house wren may use other than the traditional nesting materials. Mrs. Gilbert Drake (1931) describes a nest built in a chicken house in West Park, N.Y., that consisted largely of small pieces of rusted chicken wire. A nest observed by Helen P. Williams (1931) was made up entirely of metal consisting of rusty bent nails, double-pointed tacks, and pieces of wire. An analysis made of a nest found at Ames, Iowa, by Harriet C. Battell (1925) was made up of the following rubbish: "52 hairpins, 68 nails (large), 120 small nails, 4 tacks, 13 staples,. . .10 pins, 4 pieces of pencil lead, 11 safety pins, 6 paper fasteners, 52 wires,. . .1 buckle, 2 hooks, 3 garter fasteners, and 2 odds and ends." Goelitz (1918) reports finding a nest made up entirely of rusted pieces of wire. In fall a tangle of rusted chicken wire was thrown behind a shed, and the following spring a pair of house wrens in search of nesting material found that the wire would break easily into pieces just suited for the purpose. The birds used this wire to the practical exclusion of all other usual materials.
The house wren has the habit of frequently building dummy or extra nests, a trait common to other members of the wren family. Many of these nests are built by the male prior to the arrival of the female in the spring, but a mated male may use its superfluous energy in building extra nests in the neighborhood of the one where his mate is incubating the eggs. Even if a male is unsuccessful in obtaining a mate, he may continue to build several nests during the course of the season. The nests built by the male are crude structures, and it is probable that some of the curious nests made of rusted wire nails and other metallic material previously described are to be attributed to the work of the male. In central Illinois I observed both members of a pair of wrens build three complete nests in different boxes before selecting one for final occupancy.
Mrs. Daisy Dill Norton (Forbush, 1929), of Lewiston, Maine, reports a case in which an unmated female built a nest in a bluebird house. It went through all the manifestations of a maternal wren with a family in prospect. She allowed no birds on her house or near the nest and was ready to do battle with anything that appeared regardless of size. The wren remained until the end of August, and in all this time Mrs. Norton never saw another wren, nor did she hear the song of the male. After the wren left, the box was taken down, and inside was found an exquisitely built nest containing 12 (sterile) eggs. From these observations it is apparent that the nesting instinct is strongly developed in both the male and female house wren.
One cannot watch a pair of wrens in their repeated attempts to get long unwieldy sticks through a narrow box entrance scarcely large enough to admit their tiny bodies without being greatly impressed by their dogged persistence, energy, and skill. At first the wren, especially if it is a young individual, may attempt to enter a nesting hole with the beak grasped at the center of a long twig, but very quickly through trial and error it learns to thrust one end of the stick through the opening and then to inch it along with the beak until well inside the nesting box. After the technique is mastered it is not unusual for them to add four or five such sticks during the course of a minute. In a single day they may accumulate a mass of sticks several inches in depth, and in 2 or 3 days the entire structure is completed and ready to receive the eggs.
Eggs.--The number of eggs in complete sets varies from 5 to 12, but the range in numbers is usually 6 to 8 in the vast majority of nests. Harlow (1918) in reporting on 47 nests of the house wren found in New Jersey and Pennsylvania states that the average set was 6 or 7 eggs, but in his series there was a range from 5 to 8 eggs in complete sets. Baldwin (Baldwin and Bowen, 1928) found that of 21 pairs that had two broods that he had under observation, the average was 6 eggs for the first and 5.5 eggs for the second brood. Of 19 pairs known to have but one brood the average number of eggs laid was 6.3 per female.
Birds may be classed as determinate with respect to egg production when they lay a definite number of eggs in a set and indeterminate when they can be induced to continue laying by egg removal. Cole (1930) found that if eggs, presumably from the same female house wren, were removed daily, the bird laid an unusually large number of eggs. Detailed measurements he made revealed that the length of the eggs increased in general to a certain point, then rested, then increased to a second high point, then rested, and for a third time increased to a high point; following this there was a downward trend. Thus there appeared to be four cycles, separated by rest periods. It is suggested that the process of incubation may react on endocrine glands to cause cessation of egg production.
The eggs vary from short-rounded-ovate to oval in shape. The ground color is white, usually with a vinaceous tinge. They are thickly speckled with minute dots of brownish red or cinnamon-brown, which are often so dense as to conceal the ground color giving the entire egg a uniform salmon-colored or reddish-brown cast. The color is deepest at the rounded end, and in many eggs there is a wreath of spots concentrated around this end of the egg. The eggs vary in their long diameter from 0.58 to 0.70 inch and in their short diameter from 0.46 to 0.53 inch. The average dimensions of 100 eggs are 0.64 by 0.50 inch. The measurements of 50 eggs in the United States National Museum averaged 16.4 by 12.7 millimeters; the eggs showing the four extremes measure 18.3 by 13.2, 15.8 by 15.5, 14.7 by 12.2, and 16.3 by 11.7 millimeters.
The house wren has two distinct breeding periods. The first, according to Kendeigh (1940), who has made very extensive observations at the Baldwin Bird Research Laboratory, Cleveland, Ohio, begins in the middle of May and lasts until the end of June; the second begins late in June and lasts to the middle of August. Egg-laying occurs most regularly during the first 2 weeks of each period, but occasional sets may be deposited at any time. One egg is laid each day during the egg laying period until the full complement of eggs is completed. Certain observers have credited the house wren with as many as three broods in a season, but these cases are unusual, and it is extremely doubtful whether three broods are ever successfully reared.
Young.--The incubation period of the house wren is 13 days. The egg temperatures in the nest of the house wren according to Kendeigh fluctuate between 33.9 C. and 36.9 C. The temperature of 35 C. may be considered the temperature at which incubation to hatching is normally accomplished in 13 days. Based on the rate of gaseous exchange the most favorable incubation temperature for rapid development falls between 35 and 37.8 C. On the basis of Kendeigh's computations, if we take into account the total amount of oxygen absorbed and assume the respiratory quotient to be 0.72, development at a controlled temperature of 37.8 C. would require only ten days, while at 32.2 C. it would require 18 days. Temperature is an important factor in determining the length of incubation. Reports by different observers present a variation in length of the incubation period from 11 to 15 days, but this discrepancy can be explained in part through the lack of proper consideration in the factors involved and especially through the lack of accurate determination when incubation actually starts.
Baldwin and Kendeigh (1927) made a detailed study of the behavior of nesting house wrens, including their attentiveness and inattentiveness. Their information was obtained by direct observations and from continuous records secured by the use of special apparatus involving the principle of thermoelectricity to determine the presence or absence of the birds from the nest. It seems desirable to quote their statements at considerable length.
The differentiation between the periods of attentiveness when the bird is actually engaged in nesting activities and the periods of inattentiveness when it is feeding or resting is best developed with the female for it is she who is most active in the reproduction of the species.
After the female becomes mated with the male, she soon begins to carry in lining for the nest, the rough part of which has been begun or finished by the male some time previous. The female, however, does not carry nesting material into the box continuously for long at a time, getting her food at odd moments when she is looking for material. On the contrary, she works assiduously at building the nest for a period of a few to several minutes, and then goes off and hunts actively for food for herself, only to come back when this period is ended to carry more material for another stretch of time, and so on. While building her nest she is not concerned with looking for food. Likewise, when she is away looking for food, she does not concern herself with nesting duties. She usually spends a great deal longer time away from the box than at the box during this phase of her nesting activities.
The same holds true for the days during which she is laying her set of eggs. Her inattentive periods are usually much longer than her attentive periods, although she comes to the box at regular intervals throughout the day. As her set nears completion and the duties of incubation approach, the inattentive periods gradually shorten, and the attentive periods not only lengthen but become more numerous.
The day on which the eggs hatched the activities during the early morning started at the normal rate. However, at one nest studied, beginning at 7:11 her record indicates considerable uneasiness.
The reason for this became apparent when at 7:35 the first young bird was found to have just broken out of the shell. All of her eggs hatched during the rest of the day. The number of her attentive and inattentive periods during the day was 81, although the average number per day during the incubation period had been only 43 1/2. The unusual restlessness, however, was exceptional, since our records for other females are much steadier.
The female during the next few days gradually resumed her normal rate of activity. During the next 6 days when she spent considerable time brooding the young, the periods of attentiveness averaged about 13 8/10 minutes and her periods of inattentiveness about 4 6/10.
When both adult birds were busy from morning till night with the feeding of the young, periods of attentiveness and inattentiveness still were the rule. The adults would feed the young several times in succession and then take a short period off when they would get some food and rest for themselves. Sometimes they would feed the young repeatedly and rapidly nine, ten, or more times before they would stop. Then again the number of feedings per period would be only three or four, and in many cases, but one. Usually the number of feedings per period averaged higher in the morning than in the heat of the day.
Baldwin (1921) through his exhaustive banding operations at Cleveland, Ohio, has shown that house wrens are not permanently mated. Not only do they change mates from season to season but also they shift mates between the two nesting periods of the same season. His banding records indicate also that the house wren breeds the season after hatching when it is one year old. Out of 156 wrens banded during the 5 years between 1915 and 1920, 10, or 6 2/3 percent, returned either to the same or to other nesting boxes on his premises. In more recent banding results Kendeigh (1941) reported a 75 percent return ratio of adults. Baldwin observed the details of the life history of seven different nests of which the following is typical: The nest was started on July 4 and completed 2 days later, July 6. The set of eggs was completed on July 13 and hatched on July 26, an incubation period of 13 days. The young left on August 10 after spending 15 days in the nest. The total cycle required 36 days.
Col. S. T. Walker, of Milton, Fla., made the following detailed observations of a pair of nesting house wrens (Ridgway, 1889):
I was sick at the time, and watched the whole proceeding from the laying of the first stick to the conclusion. The nest was placed in one of the pigeonholes of my desk, and the birds effected an entrance to the room through sundry cracks in the log cabin.
The time spent by the young in the nest, as reported by various observers, varies from 12 to 18 days. Burns (1921) states the complete nesting cycle of the house wren is 35 to 45 days, whereas Bewick's wren and the chickadee require 52 to 53 days.
Baldwin and Bowen (1928) state that out of 104 nests under observation at Gates Mills, Ohio, 86 broods were successful. "The total number of eggs laid by all females under observation was 581. Of these 424 or about 73 percent hatched, and 390, or about 67 percent left the nest as normal young. The remaining 33 percent perished at one stage or another."
The instincts of the house wren are so strongly developed in certain individuals that curious situations sometimes occur. Mrs. Bridge (1911) reports a single pair of birds nested on her premises, but two nests were constructed, one in a gourd and the other in a birdhouse. When the young were hatched the brood in the birdhouse were fed by the male alone but the young in the gourd were fed by both members of the pair. The inference is that after the female laid both sets of eggs she incubated the eggs in the gourd while the male took care of those in the box.
Kendeigh (1941) records cases of multiple nesting as follows:
Although the female ordinarily remains with the young until they become independent, there is a tendency towards the end of the first period when the nestlings are being cared for in the box for the female to begin preparations for a second brood. She may inspect other boxes either of the same male or of other males in different territories. If acceptable, mating may occur very soon, nest-lining inserted, or even egg-laying begun before she is through caring for her first brood. It is but a small step to actual desertion of the first brood by the female in order to start a second brood that much sooner, but desertion does not ordinarily occur without provocation. When the female leaves, the male will ordinarily care for the young alone. He mostly stops singing and applies himself assiduously to the task of hunting food for his offspring. However, he does not brood nor does he stay in the box at night. If the female deserts before the young have acquired self-regulation of their body temperature, death usually follows, but after a week's development, the male is often able to bring them off successfully.
It has been observed that house wrens that for some reason or other fail to raise a brood of their own, and sometimes individuals that do not succeed in obtaining a mate, will satisfy the urge for caring for offspring by feeding the adults or young of other species. Hills (1924) reports a case in which a house wren fed the adults of young of grosbeaks as well as a family of English sparrows. His account is as follows: "The female Grosbeak was on the nest and a House Wren was bringing small caterpillars to her, which she took from the Wren's beak and fed to her young. At first it seemed to me as though the Wren was liable to be cited as co-respondent, but soon the male Grosbeak came and relieved his mate on the nest, yet the Wren continued to come with food which the male Grosbeak likewise received and fed to the young. . . . Both of the Grosbeaks sometimes themselves ate the Wren's offerings, in place of feeding them to their young. The Wren made more trips to the nest than both Grosbeaks combined." After the young grosbeaks left the nest the wren persisted in feeding them directly. A few days later this same wren was observed feeding a family of English sparrows.
There is evidence that polygamy may be practiced among house wrens. Kathleen M. Hempel (1919) gives an account of two families of wrens that were served by one male. The lone male carried food to both females during the course of incubation and assisted in feeding each of the broods of offspring. John W. Taylor (1905) cites a similar case at St. Paul, Minn., in which a male wren carried food to two nests, one located in a stump and the other about 60 feet away in a birdhouse. Metcalf (1919) writes that he had eight house wren nests on his place at Foreston, Minn., but at no time did he observe more than two males.
After the young leave the nesting box in which they were reared, they seldom return, but many observers have reported seeing the entire family brood rounded together by the parents, at the end of the day, to roosting places. These places may be other nesting boxes, a platform provided by an unused robin's or chipping sparrow's nest, or the dense foliage of a pine tree or shrub. Such roosts may be used for a week or more before the family disperses and the young assume a more or less independent role. Usually the adults remain with their young about 12 or 13 days, and for the first part of this period the parents feed the young practically everything they receive. During the last few days of this period they acquire the ability to hunt food for themselves, and the parents spend less and less time with them. Finally, when the young are able to take care of themselves, the relationship of parent to offspring ceases and becomes that of individual to individual.
Plumages.--The natal down is sepia brown in color. This first plumage is very scant, being represented in typical specimens by not more than 25 neossoptiles or down feathers. Of these there are five on each side of the crown and four on each side of the occipital region. On the back of the bird there are three on each side and usually a single one at the posterior end of the median line.
The down undergoes disintegration by wear and abrasion in the nest, and by the time the young are ready to fly only a few filaments remain attached to the tips of the juvenal feathers. The juvenal plumage of the house wren is described by Dwight (1900) as follows: "Above, Prout's-brown, russet tinged on the rump and deep grayish sepia on the pileum, sometimes faintly barred. Wings and tail Prout's-brown, darkest on the wings both with wavy, dusky barring, the palest areas on the outer primaries. Below, including sides of the head, dull grayish white with dusky mottling, washed strongly with russet on the flanks and crissum. Orbital ring dusky buff. Bill and feet buffy sepia-brown, becoming darker." The juvenal plumage differs from that of the adult in the blackish mottling of the breast, but these markings disappear with the postjuvenal molt.
Boulton (1927) has presented a detailed and exhaustive study of ptilosis of the house wren in which his general conclusions are as follows:
The first appearance of feathers and the sequence of their development in the various regions follow in definite predetermined order, constant for any one region but varying among different regions.
Development usually begins at one side or end of a region and spreads progressively over it until growth is completed.
In at least one case (primaries), development begins in the middle of the region and proceeds simultaneously toward each end.
In another case (Ventral Tract), there are two centers of development. One appears in the middle of the tract and spreads both posteriorly and anteriorly. The other starts in the inter-ramal region and spreads backward until it meets the anterior portion of the other development center. In the Spinal Tract is found a somewhat parallel case.
The feather sheath, after emerging from the skin, has no function and its rate of disintegration is primarily correlated with the amount of abrasion to which it is exposed.
The growth of feathers appears to be retarded until the second week of nestling life, but, to a large extent, this is actually due to the fact that development is going on beneath the skin during the first week and is often overlooked, while the rupture of the feather sheath and consequent exposure of the feather during the second week makes growth appear more noticeably.
According to Dwight (1900),
the first winter plumage is acquired by a partial postjuvenal moult, beginning late in August, which involves the body plumage and wing coverts, but not the rest of the wings nor the tail. The young and old become practically indistinguishable. [This plumage is] similar to the previous plumage but darker and grayer with faint barring above, the wing coverts, chiefly the lesser, with whitish spots; below whiter without mottling, the throat and sides obscurely barred with pale drab, the flanks and crissum boldly barred dull black which is bordered with russet.
First nuptial plumage acquired by wear, excessive by the end of the breeding season, which brings out the barring more conspicuously and makes the bird grayer and paler, especially below.
Adult winter plumage acquired by a complete postnuptial moult in August. Practically indistinguishable from first winter, perhaps averaging grayer with darker wings and tail.
Adult nuptial plumage acquired by wear as in the young bird. . . . The sexes are alike and the moults correspond.
Albinism and melanism, which occur frequently in many families of birds, are apparently rare in the Troglodytidae. Ruthven Deane, who gave this subject a great deal of attention, knew of none and emphasized the absence of these plumages in certain families, including the Troglodytidae. He offered no explanation for its absence. In a search through the literature I have failed to find a single record of an albinistic or a melanistic form of the house wren. Hence these phases of plumage in this species are remarkable for their rarity if not their absence.
Wetmore (1936) counted the number of contour feathers in various passeriform birds including two house wrens. A male secured on June 11, 1933, weighing 13.3 grams had 1,271 contour feathers, the latter weighing 0.6 gram. Another male, obtained on July 9, weighing 11.5 grams, had 1,178 contour feathers weighing 0.7 gram.
Poole (1938) in studying the ratio of wing area to weight and the effect of this ratio on flight, determined the wing area of a house wren weighing 11.0 grams to be 48.40 square centimeters. The wing area per gram is shown to be 4.40 square centimeters. As a means of comparison, it is interesting to note that in the case of the loon, a poor flier, there is the ratio of only 0.56, while that of Leach's petrel, which spends much of its time in flight, has a ratio of 9.47. ***
Food.--As far as its feeding habits are concerned, the house wren may be considered entirely beneficial to the interests of mankind. The food is almost all animal life, the small amount of plant material found in stomach examinations being purely incidental and taken in the course of capturing insects poised on the vegetation. Much of our knowledge of the food habits of the house wren is based on field observations, but the most precise information we have has been derived from the detailed analyses of the stomach contents of individuals collected in all sections of the distributional range of the species.
According to Beal (1897), 98 percent of the food is made up of insects or their allies and only 2 percent is vegetable matter. One-half of the food consisted of grasshoppers and beetles, the remainder caterpillars, bugs, and spiders. The examination of 68 stomachs of house wrens, reported in a later publication by Beal (Beal, McAtee, and Kalmbach, 1916), substantiated the above findings. The largest four items taken in order of their amounts are bugs, grasshoppers and related forms, caterpillars, and beetles. The bugs, made up chiefly of stinkbugs, negro bugs, and leafhoppers, constituted 29.34 percent of the food. Grasshoppers, crickets, and locusts are represented in the food throughout the season and aggregate 17.61 percent of the food. Moths and caterpillars, including such forms as cabbage worms and gypsy moths, make up 13.9 percent, and beetles trail closely in amount at 13.8 percent. Ants are eaten to the extent of only 8 percent of the yearly food, but during March they are more significant, being represented in that month by 22.67 percent. Bees, wasps, and flies are taken in smaller amounts; evidently these types of insects are left for the fleeter flycatchers and swallows. Spiders are very acceptable and are captured every month in the season. The latter are found by the inquisitive wrens while searching and exploring under piles of lumber or brush, stone walls, hollow logs, outhouses, and sheds. Only a mere 3 percent of the insects eaten can be considered useful as enemies of destructive species of insects.
In addition to the above-mentioned items of food, small numbers of millipeds, ticks, lice, aphids, snails, and small crustaceans are sometimes included in the diet. There is no evidence in the examination of stomach contents that the wren eats fruit or other farm products, thus placing it high in the group of our beneficial birds.
The nestlings are fed very frequently and consume enormous quantities of food. Judd (1900) made field observations of a brood of three wrens that were housed in a cavity of a locust tree at Marshall Hall, Md. The nest with its family was transferred to a baking-powder can nailed to a trunk of a tree to facilitate the observations. In the course of 4 1/2 hours the mother wren made 110 visits, during which she delivered 111 insects and spiders. Among those identified were 1 white grub, 1 soldier bug, 3 millers (Noctuidae), 9 spiders, 9 grasshoppers, 15 mayflies, and 20 caterpillars. On the following day similar observations were made from 9:35 a.m. to 12:40 p.m., during which time the young were fed 67 times. The food included 4 spiders, 5 grasshoppers, 17 mayflies, and 20 caterpillars.
Jones (1913) observed a pair of wrens feeding their young for a period of 65 hours, during which there were 667 visits to the nest, 560 by the male and 107 by the female. "There were 637 [641?] pieces of food brought"--161 geometrid larvae, 141 leafhoppers, 112 young grasshoppers, 56 bugs, 42 spiders, 29 crickets, 10 moths, 5 ants, 4 miscellaneous, and 81 pieces unidentifiable; and 29 visits were made without food.
McClintock (1909) observed a wren feeding her nestlings considerable numbers of blue-bottle flies. Sometimes the flies were stripped of their legs and wings, but oftener they were fed intact.
Perhaps a record for number of feedings by an individual wren in one day is that of a male bird observed by Clara K. Bayliss (1917) at Macomb, Ill. The pair of wrens nested in a bird box nailed to a disused poultry house. The female disappeared, probably killed, after the brood of seven was hatched. On June 26, when the young were 12 days old, the lone male bird, during a continuous all-day watch from 4:25 a.m., the time of the first feeding until 8 p.m., when activity ceased, made 1,217 visits to the nest with food. During the hour from 9:15 to 10:15 a.m. the bird made a record of 111 visits to the nest, or an average of nearly two visits every minute.
Similar observations by various other observers confirm the large number of visits made to the nests by the adult birds, indicating that enormous quantities of food are consumed by the young. Indeed the young as well as the adults spend the major part of their daylight hours in the serious business of feeding.
Stevenson (1933) has shown that the stomachs of the young are consistently larger than those of the adults and has proved the greater food-carrying capacity of young birds over adults. Through a large series of measurements he has found that the average length of the intestine of a house wren one day old is 4.2 centimeters, and by the time it is 11 days old it reaches a maximum of 12.5 centimeters. He finds the value obtained by dividing the length of the intestine by the body weight decreases from 2.80 at the time of hatching to1.31 at 11 days. There is a gradual decrease in this proportion with increasing age until the birds become adults. Tests indicate that food passes through the entire alimentary tract in approximately 1 1/2 hours, and thus the food supply must be constantly replenished. Stomachs examined at all hours of the day reveal that they are seldom empty and indicate that food is taken repeatedly even though the stomach already contains food.
Hervey Brackbill, of Baltimore, Md., has attempted to ascertain the source of the food brought to the nestlings. He carefully watched the adult bird during 152 feedings to determine the places of its foraging. The parent flew out of sight on 107 occasions, but in 45 instances he was able to follow the bird to its hunting grounds. On 21 of the trips it went to the ground, a clipped lawn, wild land covered with tall grass and weeds, and the gutter of an asphalt-paved road. Twenty times it secured the food from a tree, one time climbing up the trunk of the nest tree after the fashion of a brown creeper to pick off a moth. It resorted to a bush three times, and once it hawked its prey by flying out in a swift loop from the nest tree.
Voice.--The loud clear song of the house wren is one of the dominant characteristics of its striking personality. The Chippewa Indians, who were keen observers of nature, fully recognized this trait as revealed by their name for the house wren: O-du-na-mis-sug-ud-da-we-shi, meaning a big noise for its size (Cooke, 1884).
The scolding or alarm note of the house wren is a harsh, grating chatter, but the song is a burst of melody, a rather loud, hurried, strenuous, bubbling outpouring--shrill, ecstatic, and difficult to describe or to translate into written words. It is a varied song, but to human ears it is not musical or nearly so appealing as that of its relative, the Carolina wren. The persistent repetition of its nervous energetic outbursts has after a time a tendency to tire the listener.
Dr. Winsor M. Tyler, in correspondence, writes of the song as follows: "The house wren's song is a simple little smooth-running strain, a common form begins with the chatter of rapid notes and then, without pause, runs down the scale in a cascade of seemingly doubled notes. The syllables tsi-tsi-tsi-tsi-oodle-oodle-oodle-oodle suggest it somewhat. It varies in form a great deal in minor details and is often full-bodied in tone of voice, but it is practically always delivered with the customary gush and tiresome reiteration. When disturbed, and it takes little to disturb a house wren, the bird bursts forth with a sharp, tense chatter of the Baltimore oriole, or with a long series of nervous fidgety chip notes."
In correspondence from Aretas A. Saunders, he presents an excellent analysis of 55 records he made during his extensive study of the songs of the house wren. His remarks follow: "While the song of the house wren is very variable, it most frequently consists of a series of very rapid notes, the pitch rising at the beginning, falling toward the end, with a sudden increase in loudness on the highest notes in the middle of the song. There are commonly groups of three to eight repeated notes on the same pitch. Some of the songs contain trills, but the majority do not. Twelve of my 55 records contain trills, that is, places where the notes are so rapid that the single notes cannot be counted. With these 12 records omitted, and six others that are unusual and all from the same bird, the remaining 37 records average 16 notes per song, the least being 11, in five records, and the most 23 in only one.
"The pitch of my records ranges from D''' to B''' and a great majority have the highest and loudest notes on A'''. The average song ranges from about two and a half tones from the lowest to the highest note. The greatest range of any one song is four tones, and the least one and a half. One unusual song is not considered, since it is all one pitch and therefore has no range. The songs on my records range from 1 2/5 to 2 3/5 seconds in length. The rapid notes seem to be about eight per second in most cases."
Hervey Brackbill, of Baltimore, Md., has observed the house wren sing during the course of its flight. He states: "During May I saw a house wren burst into song on the last 2 or 3 yards of a 50-yard flight from tree to tree, completing the song without interruption after alighting. Again, one or two that were keeping close company several times continued songs while flitting from branch to branch, and once this bird began a song about a foot from the finish of a 5-yard flight."
At the height of the singing season the song is repeated with an amazing frequency. In one timing of the song of a male of a pair that nested in a box on an Illinois farm, the full song was repeated three to four times every minute and at one time totaled five times during the course of one minute.
The house wren begins its singing at an early date even before its departure from its winter to its summer haunts. Kopman (1915) writes that it sings freely for 3 weeks or more in its winter retreats of Louisiana before leaving on its northern migration.
Early in the spring one may find a house wren singing a song that is an irregular indefinite jumble of notes, only slightly or not at all suggesting of the usual song of the species, which has been referred to as a "primitive" and by others as an "abnormal" song. Saunders (1929b) relates an interesting experience with a house wren singing these abnormal songs at Fairfield, Conn., as follows:
[The] song was like that of no bird with which I am familiar. In fact the bird possessed nine different songs, no one of them normal, although one or two had a wrenlike suggestion in them. One began with five long, loud whistled notes, a little suggestive of some notes of the cardinal. Another began with two such notes and two others and ended with a single note of this character. One was a series of slurs and somewhat suggested a Swamp Sparrow. Another in form but not in voice, was like a Song Sparrow song, yet no one of these songs suggested any of these birds clearly enough as to make me think them imitations. All these songs were recorded between June 4th and 17th, after which the bird disappeared. When I first heard this bird I had not the slightest idea what species was producing the song.
The song of some birds ceases or deteriorates with the completion of the set of eggs and the beginning of incubation, but in the case of the house wren the full song is continued with great frequency even when the young are being fed. Saunders (1929b) has presented an interesting interpretation of this continued singing from the standpoint of function. During the early part of the breeding season it serves as a territory song, but later when the young appear it acts as a stimulus in prompting the young to a feeding response. Saunders writes as follows:
Many have undoubtedly observed the incessant singing of the male House Wren when feeding young and the habit of approaching the nest with a bill full of insects and singing just before entering the door, without dropping any of the insects. This explains why the bird has this habit. The song at that time does not differ materially from the territory song of earlier spring but it is no longer a territory song, but a stimulus for the young. According to my own observations during the early nest life of the young House Wrens, the male gathers the food and the female stays in the nest with the young, probably brooding, the male passing the food to her at the entrance. Later, when the young are older and need no stimulus, but need a greater quantity of food, both parents gather food and feed the young.
According to correspondence received from A. D. DuBois, the notes of the male, at the time when the wrens had young, changed to a shorter simpler strain consisting principally of two tones: a succession of high notes followed by a succession of low notes.
The song of the house wren is continued to a time well beyond the nesting season. The bird is in full song until the last week of July and then tapers off into August, but it continues to sing during most of the month and has been heard as late as November 5. Evans (1918), a florist at Evanston, Ill., left the door of his greenhouse open in the fall. A house wren entered, and in the evening the song was heard. The bird remained all winter, and the song was delightful in zero weather of January. These late songs, however, are different, often exhibiting a decided change in quality and volume when compared with the territory song. Likewise, the song has none of the spontaneity and vigor of the spring song; rather it is a low rambling warble. They are abnormal songs resembling those that are sometimes heard early in spring. Likewise there comes at this time a correlated change in the behavior of the birds. They no longer cling to the vicinity of human habitations and are more apt to be found inhabiting the rocks and shrubs of wild and unfrequented localities.
Albert R. Brand (1938) has made recordings of numerous bird songs on film, a medium from which sounds can be studied objectively. Such a film reveals a picture of the number of vibrations per second that determines the pitch of sound. He has found that the average pitch of passerine bird songs is 4,280 vibrations, or a quarter of a note higher than C7, the highest note on the piano keyboard. The approximate mean of the notes of the house wren is 4,100. The highest note in its song reaches 7,125, while the lowest is about 2,050 vibrations per second.
In the table below are Brand's determinations of the pitch of
the song of the house wren when placed alongside those of the
crow, which has a low-pitched voice, and those of the black-polled
warbler, a bird with an extremely high voice. This table will
serve to facilitate a comparison in the pitch of these three very
Enemies.--As is true with many birds, the house wren is host to a number of external parasites. Peters (1936) lists five species as having been found on the house wren: Two lice, Menopon sp. and Philopterus subflavescens (Geof.), and three species of mites, Dermanyssus gallinae (Deeger), Liponyssus sylviarum (C. & F.), and Trombicula whartoni (Ewing). While the presence of lice and mites is not usually fatal to the birds, heavy infestations are very annoying and may prove harmful, especially to nestlings, which have no means of ridding themselves of the pests.
Baldwin (1922) cites a specific example in which there was a lone house wren in a nest that received all the food and attentions of the adult birds. This nestling, instead of growing rapidly in size and weight, as might be expected, was far below normal, greatly undernourished, and a miserable skinny-looking specimen. This condition prevailed until a heavy infestation of lice was discovered and a poultry-louse killer applied on the twelfth day. After that there was some improvement, and a considerable gain in weight was noted.
No records of internal parasites and diseases of the house wren have come to my attention, but doubtless a thorough examination of many specimens would reveal them.
Nests of the house wren have been found by Mason (1936) to be infested by the larvae of the blood-sucking fly Protocalliphora splendida sialia. These larvae have been found to be very destructive to the young of such box-nesting species as the bluebird and tree swallow. The nests of the wren are less favorable for the parasites, but even so they have proved to be an important factor in the mortality of nestling wrens. This has been found to be especially serious when the infestations are accompanied by other unfavorable conditions such as bad weather, and lack of food which tend to lower the resistance of the young. These flies are not known to be carriers of diseases, but, when present in sufficient numbers in a bird's nest the larvae often suck enough blood from the young birds to bring about their death.
In the examination of 39 nests of the wren a total of 201 larvae and puparia were found. A secondary parasite, which serves as a natural check on Protocalliphora, is the chalcid Mormoniella, and it is thus desirable to give this little fly every opportunity to increase in numbers. When heavy infestations of the blood-sucking fly Protocalliphora occur, it is important to clear the nesting boxes after the young are four or five days old.
It is well within the range of possibility that pests such as Protocalliphora have been an important factor in the local disappearance of the wren in sections of New England where the English sparrow has shouldered most of the blame.
Spiders hatched from egg sacs carried into the nests with sticks sometimes prove a menace to the wrens. Hathaway (1911) gives an account of a pair of wrens that were driven away by spiders. His story in part is as follows:
About a week after I missed the delightful song, so I started to investigate. Rapping on the stub no bird appeared, and soon I saw that the edges of the hole were alive with small spiders. I took the stub down and examined it, and found the nest swarming with these spiders. The birds in building the nest had used small twigs entirely and had thickly stuccoed them with the white egg sacs of a species of spider, that had hatched before the wren had deposited her own eggs, and instead of making a home for her young, she had unwittingly gathered together a fine family of spiders and provided them with a well-sheltered retreat.
Cats rank as enemy No. 1 of the house wren. Since these birds nest about human habitations, especially on farms, where cats are common, they fall prey to them oftener than do species of birds nesting in remote localities. Cats are especially destructive to young when they leave the nest prematurely. Reports of adults falling victim to cats are common, but young are always in imminent danger of the ravages of these bird destroyers. I vividly recall seeing a cat seize two young wrens in rapid succession when a brood of seven were startled from the nest before some of them were able to fly well. The unfortunate youngsters landed on the ground where a prowling cat was poised for action.
Errington (1935) reports finding the remains of house wrens in the stomach contents of red and gray foxes; hence individuals inhabiting places remote from the houses of man are also subject to prey by predatory mammals. Wrens are also preyed upon by predatory birds such as owls; Fisher (1893) reports finding the remains of a house wren in the stomach contents of a screech owl, and Errington (Errington et al., 1941) found three wrens in the pelletal remains of the horned owl.
While the house wren is notorious for its aggressions toward other birds, sometimes the tables are turned and it is driven away by huskier intruders. Henderson (1931) reports that Carolina wrens nest in boxes at his home, located near a heavy forest at Greensburg, Ind. Although house wrens attempt nest-building on his premises, they have been completely driven out by the Carolina wrens. The same can be said for Bewick's wren in the southwestern section of the range of the house wren, although in some localities the situation is reversed. In the past the English sparrow has offered the severest competition. Indeed, the scarcity of the house wren in certain sections of its range, especially in New England, has been attributed to this persistent and audacious marauder. Knight (1908) states that the house wren was a common bird near Bangor, but at the advent of the English sparrow the species began to diminish about 1885 and none have occurred there since 1887. Similar conditions prevailed in Massachusetts. In recent years since the marked decrease in English sparrows the house wren is coming back and is now nesting in sections where for years it was virtually extirpated.
Other birds have had their innings with the house wren, and even the midget of a hummingbird may spend its wrath on it when occasion arises. Hervey Brackbill submits the following interesting experience: "One late August day I came upon a wren under attack by a ruby-throated hummingbird. Scolding, the wren was hopping and flitting from one place to another close in to the two main stems of a small locust tree while the hummer--apparently unable to follow it through the twigs directly--darted in at it from the outer edge of the tree, then shot back out again to strike in through some other opening at the wren in its new position. The hummer made half a dozen thrusts within the next few minutes; then the wren apparently found a safe spot. The hummer perched for a while, in near the heart of the tree, then flew off."
Snakes are not a common enemy of the house wren, but the following experience of Hunter (1935) is interesting: "Last spring on one of my nature rambles at West Point, Ill., my attention was drawn to the nest of a pair of House Wrens. . .by the alarm notes of the owners. Upon making an investigation I found it necessary to remove a Garter Snake. . .from the nest, while the process of digesting five young wrens continued uninterrupted."
Wasps, bumblebees, field mice, red squirrels, and chipmunks have also been cited as troublesome to nestling house wrens.
Friedmann (1938) has reported two cases in which the house wren has been host to the eggs of the parasitic cowbird. The character of the usual nesting site of the house wren is such that they are seldom imposed upon by these molothrine visitors.
Sometimes man unwittingly becomes an enemy of the house wren by spraying vegetation to kill insect larvae that are eaten by the wrens. Hoffman (1925) writes as follows: "For three successive years the House Wrens have abandoned their nests in the writer's yard when their young were partly grown. The dried remains of the nestlings were found when the nest boxes received a cleaning in the fall. At the time that the nests were abandoned the currant bushes had become infested with the small green currant worms and had been dusted with finely powdered arsenate of lead. It was shortly after the old birds were observed carrying the arsenate-covered worms to their nests that they disappeared and were not seen again."
Philp (1937) reports that house wrens among other birds were blackened by smudge made during a cold wave to protect fruit from a threatening frost. The carbolic acid in the crude-oil vapor that covered both their food supply and their plumage was not enough to prove fatal to the birds, but Philp states the birds were so saturated with the greasy oily deposit that they could not regain their normal colors until the following molt.
During migration fatalities frequently befall the house wren when it flies into lighthouses and tall city buildings. Overing (1938) reports that a house wren was killed by flying against the Washington Monument, thus sharing the fate of many other species of birds. Sometimes wrens are carried out to sea by storms. Sprunt (1931) states that a house wren came aboard a ship when it was well out to sea off Cape Lookout, N.C. It crept under the winches and about the mooring bilts for the better part of an hour.
Fall.--In September the house wren, as we know it as a tenant in our nesting boxes during summer, undergoes a marked change in behavior, in song, and in plumage. At this time it deserts the environment of man and resorts to the deep recesses of the woodlands, where it skulks among the tangled underbrush making its presence more difficult to detect. The song as previously noted may continue, but it undergoes considerable modification. Its plumage is grayer and darker than the garb worn in summer. Little wonder that Audubon thought the bird he observed at this season to be a different and a distinct species, which he described as the wood wren.
In New England and in most of its summer range the last house wrens remain until the middle of October, but the majority of them have departed for their winter quarters in the southern states before this time. A few may linger until the first week of November. On November 5, 1941, one was seen and heard singing at Kingston, R.I., and another was observed on November 7, 1938, at Amherst, Mass., a record for the last-seen house wren in the region. According to A. H. Howell (1932), the first house wrens reach their haunts in Florida during the last week in September or the first week of October. His earliest two records are of one seen at Oxford on September 26, 1928, and one at Orlando on September 27, 1909.
It has been claimed that the name of the House Wren is a misnomer, because in the south during the winter these birds are found in the forests miles away from the nearest habitation. This, however is owing to circumstances over which the House Wren has no control. He is just as much of a House Wren in the south as he is in the north; you will find a pair in possession of every suitable dwelling. The difficulty is that in the winter there are more House Wrens than there are houses, and being of a somewhat irritable disposition, the House Wren will not share his quarters with others of his kind. Late comers, therefore, who cannot get a snug nook about a house or outbuilding, are forced to resort to the woods.
A. H. Howell (1932) writes of the house wren in Florida as
follows: "This little wren, well known in the North as a
conspicuous inhabitant of orchards and dooryards, loses most of
its familiarity while resorting in the South, and during the
winter months frequents palmetto thickets and brushy tangles in
the hammocks. Here the birds are shy and for the most part quiet,
but as spring opens one may occasionally hear snatches of the
bubbling song, which on the breeding grounds is a nearly
continuous performance." In Alabama, Howell (1924) states
that the house wren "is quiet and rather shy, frequenting low
bushes and weed patches in the fields." Of the bird in
Louisiana Oberholser (1938) writes: "It frequents much more
commonly the forests, thickets, and swamps, where it skulks about
among the undergrowth, and is sometimes difficult to observe. . .
. It is seldom found in flocks, but most of the birds move singly
or in pairs."
House Wren* Troglodytes aedon [Eastern House Wren]
*Original Source: Bent, Arthur Cleveland. 1948. Smithsonian Institution United States National Museum Bulletin 195: 113-141. United States Government Printing Office