Contributed by Alfred Otto Gross
[Published in 1940: Smithsonian Institution United States National Museum Bulletin 176: 206-234]
The nighthawk, because of its piercing calls and the extraordinary evolutions and gyrations of its flight, attracts many persons, even the casual observers who ordinarily pay no special attention to birds. A bird so unique and striking, one that during its breeding season plays such an important role in our experiences out of doors, is destined to be the recipient of many common names.
Long before the white man came to America the nighthawk was well known to the Indians, and we find it taking a prominent place in their myths and traditions. Apparently the notes of this bird appealed most, since the names chosen by the various tribes were usually graphic allusions to the calls or to the characteristic booming noise heard during the courtship season. To the tribes along the Connecticut River this booming was the sound of the Shad Spirit announcing to the schools of shad, about to ascend the river, of their impending fate. The nighthawk was known to the Seminoles of Florida as "Ho-pil-car." In the Milicite Indian Natural History there is the name "Pik-teis-k wes," and according to W. W. Cooke (1884) the Chippewas not only had the name "Besh-que" for the nighthawk but recognized it as a species distinct from the whip-poor-will, to which they gave the name "Gwen-go-wi-a." That the Chippewa Indians differentiated these two species is all the more remarkable when we recall that this distinction was confused by Catesby and the American ornithologists of the next 50 years who followed him. It was Alexander Wilson who first noted that they were distinct species.
When the first European settlers came to our coast they compared the nighthawk and the whip-poor-will with the nightjar of their old homes, and hence we find this name in the earlier ornithological writings used as a synonym for the American bird. In certain districts of England and Scotland the nightjar is called the goatsucker, a name that originated from the queer superstition that this bird with its enormous mouth sucked the teats of goats. Like the name nightjar the name goatsucker also crossed the Atlantic, as is manifested by such names as long-winged goatsucker and Virginia goatsucker to be found in the older books and papers dealing with the American birds. The name goatsucker is still applied to the order and family but is seldom used today in designating the species.
In parts of the United States, especially in the South, nighthawks are known as bats, since the birds are usually seen at dusk when their erratic flight resembles somewhat that of the common mammal. This resemblance linked with the bellowing or booming sound produced by the wing feathers during the courtship plunge has given source to the commonly used name bullbat. Audubon (1840) used the synonym Virginia bat and stated that the French Creoles of Louisiana knew the nighthawk by the metaphorical French name "crapau volans," or flying toad. In the Bahamas, as well as in certain localities of America, a common local name is "pick-a-me-dick" a crude imitation of one of its notes. The name mosquito hawk was well earned by one individual that, according to the Biological Survey, had eaten 300 mosquitoes. Other names sometimes applied to the nighthawk but less frequently than some of those previously mentioned are pisk, pork and beans, will-o'-wisp, burnt-land bird, and bird hawk.
The commonly accepted name nighthawk probably originated because of the bird's resemblance to the smaller hawks when observed in flight. However, it has sometimes proved to be an unfortunate choice, since to the layman it suggests a bird of the true hawk type. This name on occasions has been a source of trouble to an innocent bird as illustrated in the following cases. According to B. H. Warren (1890) the Pennsylvania Game Commissioners, in their interpretation of the Scalp Act of 1885, took the stand that they were obliged to allow bounty on all nighthawks because they were known as hawks. Mr. Warren also states that there is a somewhat prevalent idea that nighthawks are destroyers of young poultry, the name doubtless having given origin to the absurdity. The following clipping taken from the Portland (Maine) Press is another example of the way the name has misled well-meaning persons. "The Press building acquired a new claim to distinction yesterday as the haunt of wild fowl when janitor Phillip Ward, upon making an ascent to the roof, discovered two hen hawk's eggs there. Apparently some bird of the genus so despised by farmers had found the top of Portland's skyscrapers the right kind of nesting place, and had laid her plans to hatch a few juvenile hen hawks up there. Janitor Ward's unexpected arrival put an end to such plans, however, and farmers may rest assured that the breed of distasteful birds who pillage their chicken yards is two the less." Arthur H. Norton, director of the Portland Society of Natural History, investigated the story and found the victim to be an innocent nighthawk. Adverse criticisms of the name nighthawk have been numerous but the name, although inappropriate, is destined to persist.
Spring.--The vanguard of the nighthawks in the spring migration reaches Florida and the Gulf States about the middle of April. There have been March arrivals reported, but these are exceptional. Large flocks, some of them numbering thousands of individuals, have been seen during May. Many of these southern records may be representatives of the southern form, Chordeiles minor chapmani.
It is not necessary to search the isolated retreats away from the habitations of man for the first nighthawk arrivals. In fact, they are more likely to appear in the midst of our populous cities and towns, where they may be seen flying high above the graveled roofs that later are to be the scene of their nesting activities.
Courtship.--The courtship of the nighthawk is an ardent and amorous performance on the part of the male. He may be seen at twilight or early dawn uttering his sharp peent calls as he flies in wide circles sometimes hovering or soaring in the air high above the proposed nesting site. At more or less regular intervals he swoops down often within a few yards of his mate. Just as he seems about to dash into the ground he makes an abrupt upward turn, the vibrating primaries producing the well-known boom. After these preliminary aerial performances the male alights on the ground or graveled roof near the resting passive female. He now stands on his feet instead of resting his body on the ground. His tail is widely spread like a fan and wagged from side to side while the body is given a peculiar rocking motion. The throat is frequently puffed out, displaying a large white patch, which is ordinarily concealed when he is at rest. Synchronized with the throat distention is the uttering of guttural croaking notes. In producing these notes the bird holds the beak tightly closed, so that the throat membrane is distended by the pressure of the air emitted from the lungs. Under these conditions the sound waves originating in the syrinx beat against the tense membrane, producing the notes of a striking and peculiar resonant quality. These notes are not uttered under ordinary conditions and constitute a very important part of the courtship.
The female, as far as outward manifestations are concerned, does not seem to be at all impressed by these extraordinary antics.The male at times in seeming desperation flies directly over the female uttering a sharp peent. He may then circle the female several times but even to this she seems unmoved. At times, when he approaches too near, the female will take a short flight, alighting a few yards away. The male follows and the performance described above is repeated. Eventually the courtship terminates in copulation.
The aerial evolutions of the male, including the downward plunges and "booming," are continued throughout the nesting period, but after the young are hatched his effervescent energies are directed in part to securing food for his offspring. With regard to the courtship of the nighthawk, Charles W. Townsend (1920b), who gave the subject of the courtship of birds careful study, stated: "The rapid headlong plunges of the nighthawk may be classed as a display of motion, a form of the dance. Incidentally, and perhaps accidentally at first, a loud booming sound is produced by the rush of air through the wing feathers. This instrumental music is now the important feature, although the dance is by no means a negligible one."
Nesting.--The nesting site, according to the procedure of a pair of nighthawks studied by me at Brunswick, Maine, is chosen by the female. A banded female returned to the same nesting site on the graveled roof of the high school building for four successive years, although the males, during at least two seasons, were different individuals.
The nighthawk is solitary in its nesting habits, though there have been instances where the nests of this species have been placed very near together, approaching a gregarious tendency. For example, E. A. Samuels (1872) states that on "a ledge of rocks back of the settlement known as Wilson's Mills, which seemed a favorable breeding place for these birds, and, in the space of every four or five rods, a female was sitting on her eggs." B. H. Warren (1890) writes that he has found several nighthawks breeding within a few yards of each other. A similar case of this kind was noted at Gardner, Maine, where five pairs of birds nested in a very restricted area of an old deserted dock. I am inclined to believe that the existence of a good nesting site rather than a social tendency is the more important factor in causing these birds to nest in proximity. In general, each pair of birds has a relatively large nesting territory, which is vigilantly guarded. I have never noted any marked tendency of the birds to flock together until after the nesting season prior to and during the migrations.
The nests of the nighthawk located on the ground are found in a diversity of situations as far as the surroundings are concerned. It prefers gravel beaches or open barren areas of rock or soil unobstructed by tall shrubbery or trees. It never builds a nest in the seclusion of a forest. In regions where forests abound it nests in places where vegetation is sparse or preferably where forest fires have left a barren waste. C. F. Batchelder (1882) found the nighthawk frequenting burnt lands in the region of the upper St. John River near Fort Fairfield, Maine, and it has also been found to be common in the burnt lands of the Restigouche Valley, New Brunswick. R. W. Chaney (1910) found a nest in a burnt-over area near a partly burned log in Mason County, Mich. I found three nests of the nighthawk in a burnt-over area near the Biological Station, Douglas Lake, northern Michigan, and C. E. Johnson (1920) saw two young on a scantily moss-covered and stick-strewn rock outcrop in Lake County, Minn., in a district previously burnt over. It has been noted that in regions that have been burnt over the nighthawk population increases; hence the burning of timber land, which is so destructive to many species of birds, is not a hindrance but possibly an aid to the general welfare of the nighthawk.
The nighthawk has also been found to breed in cultivated areas. I. E. Hess (1910) noted its nesting in plowed fields in central Illinois, and T. G. Gentry (1877) states that old stubble fields are frequently selected as nesting sites. H. J. Rust (1911) has reported the western nighthawk in cornfields in Idaho and California. The Texas nighthawk, according to Sharp (1907), is a common inhabitant of the vineyards of San Diego, Calif., where the eggs are placed on the ground under or near the vines. Nests have also been found in potato fields and even in the gardens near the houses of man. C. B. Ressel (1889) reported the eggs of the nighthawk placed upon the loose soil thrown up by the woodchuck (Marmota monax), indicating that barren places even though they are composed of loose soil may be preferred to sites covered with vegetation, twigs, and other debris.
In Virginia, according to H. H. Bailey (1913), the nighthawk often departs from its usual ground nest to a place on a stump, fence rail, or tops of drifts formed on the islands off the Virginia coast. Nests on stumps have been reported from various localities. I have found nests on the flat surface of top rails of fences in central Illinois; one of these nests was 8 feet from the ground. V. Max Kemery (1925) reports an unusual nesting site between the rails on a railroad track that was in daily use. The bird would fly when the cars or engine approached but returned as soon as the train had passed. Another unique nesting place that has come to my attention is an old robin's nest located in a tree near Farmington, Maine. This nighthawk, according to Mr. Jewell (1908), nested in this unusual site for five successive years, the tree being destroyed by fire at the end of that time.
The nighthawk in increasing numbers is availing itself of nesting sites provided by the graveled roofs of our cities and towns. In certain sections of the country this tendency is so marked that nighthawks are now seldom seen remote from graveled roofs during the nesting season, according to Lynds Jones (1909). The chimney swift, a not distant relative of the nighthawk, long ago forsook its primitive nesting sites in hollow trees, and today we no longer associate them with such places. Occurring simultaneously with the destruction of the giant forest trees was the erection of chimneys in connection with the homes of civilized races. The chimney swift, deprived of its original nesting site, was quick to make the radical but necessary change. Doubtless this adaptability to a changing environment has been an important factor in the preservation of the species. Chimneys have been used in America for centuries, but the graveled roof on which the nighthawk builds its nest is a comparatively recent development. It was not until the middle of the nineteenth century that the mansard and the flat type of graveled roofs were introduced. It was not long after these first roofs were built that the nighthawks discovered the possibilities of a new and admirable type of nesting site. As early as 1869 W. P. Turnbull wrote that the nighthawk was often seen high in the air above the streets of Philadelphia and that their nests were frequently found on the roofs of the warehouses of the city. Louis A. Zarega (1882) reported finding them breeding on a roof on the north side of 71st Street, Philadelphia, June 1882. In 1870 and 1871 Dr. T. M. Brewer (1874) found a number of instances of this bird nesting on the flat mansard roofs of Boston, and a few years later it was discovered nesting on the flat roofs of Montreal, Canada, by William Couper (1876). In 1879 a pair of the birds built a nest on a roof in the heart of the city of Cleveland, Ohio, and a few years later E. Sterling (1885) observed three pairs nesting on a slate roof of a large building near his study. Since 1880 there are innumerable records of nighthawks that have deserted the rural districts to take up their residence in the city. Today roof-nesting sites of the nighthawk seem no more unusual than the nests of the chimney swift built in our sooty chimneys. It is difficult to determine the factors that have been instrumental in this radical change, for unlike the case of the swift's hollow trees, there are just as many rocky knolls, pebbly beaches, and barren fields as there were prior to the appearance of the flat-roofed buildings. Although certain insects such as flies and mosquitoes are abundant about our cities I do not believe that the food supply has an important bearing on this question, as has been maintained by certain observers. Even in the small country villages, wherever there are graveled roofs there is the usual quota of nighthawks. In these villages the environment, as far as food for the nighthawk is concerned, is not different from regions isolated from civilization.
W. E. Saunders (1917) states that the young after their first flight often land on the ground and he asks the question: "What chance of survival is there for a young nighthawk on a city street or vacant lot?" Mr. Saunders believes that the nighthawk has steadily decreased in numbers since the bird has taken up its abode in the city and states further that immigration is the only thing that keeps up the city population. To the contrary my observations of the past 25 years in Maine indicate that the birds are not only maintaining but are increasing their numbers. Furthermore, the mortality of the birds that nest on roofs is much less than among those that choose nesting sites on the ground. In the latter place the birds are constantly exposed to the ravages of predatory animals including the cat. In the country hundreds of young birds meet with a tragic end without any of us being the wiser, while in the city such cases are more likely to be brought to our attention. On the city roof there is freedom from natural enemies. In the study of a large number of nighthawk families I have noted relatively few young that left the nesting roof prematurely, and it has been a common experience to see them return to the roof many times after the initial flight. One bird, the account of which is related in a subsequent division of this paper, returned to the roof every day until it went south on its migration at the age of 52 days. Many of the birds that nest on the roofs are never disturbed by human beings during the entire nesting period, and under such circumstances the young do not leave the security of the roof until they are able to fly well. It is obvious that the young of parents that nest on roofs are the ones most likely to survive, and they in turn will nest in similar situations the following seasons. It seems reasonable to suppose that after the habit is established natural selection and heredity play an important part in the general departure from the old to the new nesting environment.
No attempt is made by the nighthawk to construct a nest, and no materials are added to those already present on the nesting site chosen by the birds. The eggs may be in a slight depression, but no material is excavated or removed by the bird except that incidentally shoved aside by the incubating bird.
Eggs.--Normally two eggs are laid, and there is seldom a departure from this number. In a letter dated January 20, 1936, F. W. Rapp, of Vicksburg, Mich., writes that he found a nest of the nighthawk containing three eggs on May 22, 1889.
The eggs are elliptical-ovate or elliptical-oval, one end being slightly smaller than the other. The shell is strong, closed grained and moderately glossy. The ground color varies from pale creamy white to shades of cream olive-buff and olive-gray. The eggs are marked and speckled with shades of slate, black, drab, smoke and lilac gray, and tawny-olive, and some of the eggs have shades of pearly gray, lavender, and plumbeous. In some eggs the markings are fine and uniform in size, almost obscuring the ground color; in others they are less numerous but larger and more prominent. There is an endless variation in the details of the markings and colors, but the eggs in general exhibit a coloring that blends effectively with their surroundings.
The average measurements of 81 eggs in the United States National Museum are long diameter 29.97, short diameter 21.84 millimeters. The largest egg of the series measured 33.53 by 22.86 and the smallest 27.68 by 20.57 millimeters. The average capacity of nighthawk eggs, according to Walter Hoxie (1887), is 0.448 cubic inch.
The eggs do not necessarily remain in the position in which they are first laid, especially when the nesting site is on a comparatively level surface such as that provided by graveled roofs. During the period of incubation of two nests under daily observation, the eggs were gradually moved a distance of 5 to 6 feet. This shift in position comes about by the habit of the female pulling or pushing the eggs under her breast, thus moving them a short distance each time she settled on the eggs. As the direction of the bird's approach was more or less constant, the eggs were moved in the same general direction. This resulted in a distinct trail being formed, giving an appearance that one would expect to see if a giant snail had traveled over the graveled surface and forced the larger pebbles to one side. B. H. Warren (1890) writes that the eggs of a nighthawk in one instance were moved 200 feet by the bird, which carried them in her mouth. I have never been able to verify this extraordinary behavior of a nighthawk transporting an object as large as an egg in its mouth.
The following experiment is of interest as it suggests an interpretation of the manner in which a nighthawk locates its eggs. One evening when the female nighthawk was away feeding I moved the eggs to a place on the graveled roof about 6 feet from their original position. When the bird returned she alighted in the accustomed place and waddled up to the spot where she had left the eggs. No eggs being there, she went by a few inches, turned around, and recrossed the spot. This was repeated several times, and finally much bewildered she flew away. The eggs were in plain view yet were not discovered. Fearing she might desert her nest, I returned the eggs. In about 10 minutes the female returned, alighted in the usual position and without hesitation went directly to the eggs. This experiment was repeated on this and other birds with essentially the same results. It is evident that some factor such as a hypothetical sense of location or orientation is important, whereas sight plays a minor role for the nighthawk in locating its eggs. The same factor is probably important to the nighthawk in finding its way over thousands of miles during migration and its ability to arrive punctually not only in the same state and the same town but to the identical nesting site.
Incubation.--Both the male and female have been reported as sharing the duties of incubation. George H. Selleck (1916) states that the male nighthawk incubated the eggs during the daytime, whereas the female took charge of the nest at night in the case of a pair of birds he observed at Exeter, N.H. Dr. A. A. Allen (1933) states that the male takes his place on the eggs in the evening while the female is away feeding. Forbush (1927) states that both male and female share in incubation. On the other hand, J. H. Bowles (1921), who made an intensive study of the nighthawk, records only the female incubating eggs. T. G. Gentry (1887) states that incubation "is the exclusive labor of the female" but that the young are cared for by both parents. It is evident, if the above statements are all true observations, that there is considerable individual variation in the behavior of the male in regard to incubation. In my own intensive studies of several pairs of nighthawks that nested on graveled roofs at Brunswick, Maine, I have never seen the male incubating the eggs. In the case of one nest under daily observation the birds were subject to study day and night by a relay of observers for a considerable part of the incubation period. The same held true for a pair of nighthawks studied in northern Michigan. Furthermore, visits made to numerous nests revealed in those cases that only the female was incubating the eggs, although the male was often very near to the female or to the eggs. My observations agree with the statement of Gentry that the female does all the incubating, but the male in most instances assists in caring for the young.
The behavior of the birds in relation to the nest and eggs and correlated with the time of day, the weather, environmental conditions, and the activities of other birds can be illustrated by field notes taken on June 20, 1921. These notes are representative of observations taken throughout the nesting season. The nest under consideration was located on the graveled roof of a two-story high school building at Brunswick, Maine, a village of about 7,000 inhabitants located on the Androscroggin River. There are numerous giant elms and other shade trees along its streets, and the spacious yards and gardens present an environment attractive to a large number of birds. The times given throughout the following notes are eastern daylight saving:
June 20, 1921. 2:50 a.m. Cloudy, moon hidden by clouds, clear near the eastern horizon where the stars shine brightly. Entered the blind on the roof at 3 a.m. Female incubating the eggs. Her eyes were wide open when viewed with the flashlight.
3:20 a.m. The female has been quiet during the past 20 minutes but has now shifted her position and is facing northeastward directly toward the first faint light of dawn. (Daily observations revealed that the nesting bird usually faced the sunrise in the morning and the sunset in the evening. In other words, she oriented herself toward the source of light preceding the times she anticipated leaving the nest to feed. It became evident through repeated experimental tests that her leaving the nest was considerably influenced by the factor of the intensity of light.)
3:24 a.m. The male gives a loud peent call as he awakens on his perch in the elm tree. (The elm stands in the school yard and some of its branches extend over the roof wall. The male's favorite perch was on a large horizontal limb just above the level of the roof. When he was through with his activities in the morning or evening he usually retired to this limb. He generally perched lengthwise on this limb, but it was not rare for him to depart from the conventional nighthawk position and perch crosswise to the limb.)
3:40 a.m. Light growing brighter in the east, the female can be seen without the use of the flashlight. She sits with her eyes closed, but from time to time she opens them, then raises her head and peers around, as if testing the intensity of the light prior to her leaving the nest.
3:42 a.m. The male nighthawk alights on the roof and gives a sharp peent call, followed by a series of guttural awk-awk-awk notes.
3:44 a.m. The male shifts his position to the roof wall but continues the guttural calls, each time displaying his conspicuous white throat patch.
4:04 a.m. The male leaves the roof wall and alights on the graveled surface within 8 inches of the female. He utters a single sharp peent note, then continues with the striking guttural awk calls. The female shows no outward signs of being impressed by the ardent attentions of her mate.
4:08 a.m. The male leaves the roof but soon returns and is joined by a second male. Female leaves her nest and flies toward the males, and all leave under great excitement, uttering sharp, piercing calls. The female lent a hand in driving away the strange male.
4:10 a.m. The female returns and pulls her eggs beneath her in the usual manner.
4:14 a.m. The male alights on the roof about 30 feet from the nest and utters a series of awk calls in rapid succession, as if much excited as a result of his combat.
4:30 a.m. The male is chasing a strange nighthawk and, as he pursues he utters a series of yap-yap-yap-yap calls in rapid fire succession, a note I have not heard before.
4:33 a.m. The male is now going through his hair-raising dives and producing the so-called boom notes, which to me resemble swo-o-o-onk, with the accent on the last syllable.
4:46 a.m. The sun has not yet risen. The male nighthawk flies to his perch in his favorite elm tree, and thus end his activities for the morning.
9:00 a.m. The nighthawks have been quiet since 4:46 a.m. For the greater part of the time the female has been motionless, with her eyes closed, but at intervals she opens her eyes wide in response to some unusual disturbance. She did not leave to feed, as is usual for her to do each morning.
9:10 a.m. The female shifted her position and turned her eggs. I left the blind at 9:15 a.m. and my place was take by student observers, who took notes in relays until my return in the evening. They reported no activity on the part of the male. He remained on his perch in the elm throughout the day. The female did not leave the nest but merely shifted her position slightly from time to time in adjusting her eggs. When the heat was excessive she panted vigorously in order to adjust her body temperature.
7:30 p.m. When I arrived at the roof the sun was shining on the nesting female. Her eyes were opened as I approached the nest but were again closed after I had entered the blind.
8:05 p.m. The first peent call of the nighthawk is heard from the male nighthawk, perched in the elm tree near the school building, where he had retired at 4:46 a.m.
8:09 p.m. Male leaves his perch in the elm. Simultaneously another nighthawk appears from the elms farther down the street.
8:46 p.m. The male alights near the nesting female.
8:47 p.m. The female, facing toward the western sky, opens her eyes wide and turns from side to side. With this preliminary action repeated several times, she leaves the nest. The male remains within a few inches of the nest but makes no attempt to incubate the eggs. He merely serves as a guard while the female is away.
8:48 p.m. The male leaves the roof for a moment, uttering the sharp peent calls, and then returns to take up his position near the nest.
8:50 p.m. The female returns to the nest after being away only three minutes. The male was quiet a while on the roof alone, but as soon as the female returned he started his guttural notes.
8:58 p.m. The male takes leave without any ceremony and flies to his perch in the elm tree.
9:01 p.m. The female leaves the nest quietly.
9:22 p.m. No nighthawks have been seen or heard during the past 20 minutes. The female unannounced returns, after her quest for food, to brood her eggs for the remainder of the night.
Activities began again at 3:14 a.m. the next day, and the program was in all essentials similar to that recorded for June 20. Although a large series of such observations were made the male never was seen to incubate the eggs, but he regularly visited the nesting female each morning and evening. Sometimes, especially in very cloudy weather, the male left the elm tree during the day and flew about uttering the usual peent calls. He was never seen on the roof during the middle of the day.
The female was always faithful to her task regardless of a parching sun or torrential downpours of rain. At one time the thermometer placed on the graveled roof reached 130o F., although it was only 98o F. in the shade on the street level. At such times her enormous mouth was wide open, and she panted incessantly. The female's presence was needed to protect the eggs from the excessive heat fully as much as it was to supply warmth during the cool evenings when the temperatures sometimes dropped as low as 45o F. If the female should leave her eggs when the temperature rises as high as 130o F. the embryos inside the eggs would be killed in a few minutes.
It was common for the heat to melt the tar beneath the gravel so that it oozed to the surface of the pebbles. Milton Goff (1932) relates an interesting experience of a nighthawk that nested on a school roof at Rockford, Ill. One of the two eggs became firmly embedded in some tar melted by the sun. The female was unable to move the egg after nine desperate attempts made during the course of two hours.
Young.--In 1922 the nighthawks arrived at Brunswick, Maine, on May 15. On June 3 the first egg was laid and was marked No. 1. It was not incubated the first day. On June 4 the second egg was laid at 11:05 a.m. and marked No. 2. The laying of the second egg was observed. It was seen when it first appeared and watched until it emerged from the cloaca two minutes later. The egg was moist at first but quickly dried in the warm air, after which the female turned around and tucked it under her breast. Incubation began immediately after the second egg was laid.
On June 23, 1922, egg No. 1 was pipped at 8:30 a.m. and at this time the peeps of the confined embryo could be hear distinctly. At 11:00 a.m. the chick had emerged. The egg shells of the first egg were removed about noon. The female took them in her beak and dropped them during flight at a point about a hundred yards from the building. Egg No. 2 was pipped at 2 p.m., and at 3 p.m. portions of the shell were broken away. The female seemed little concerned about the first chick but lavished all her attentions on the unhatched bird. At times she elevated her body, peered at the egg, and responded to the calls of the embryo with an assuring note. She frequently rocked her body over the egg as if to assist in removing the shell. At 6 p.m. the shell was cracked latitudinally and soon thereafter the cup of the larger end was slightly lifted. At 6:30 p.m. the young was completely freed from the shell, which broke away in two parts. As the shell membrane dried the two cups closed again forming a complete empty shell case. At this time the first young was being brooded while the second, in a wet bedraggled condition, awkwardly and weakly wavered its head beneath the bill of the female. The faint peeping notes uttered by the youngster were answered with guttural purring notes of the proud and triumphant mother. After the down of the second youngster was dry it joined its fellow under the breast of the mother. The egg shell was not removed until the following morning. The incubation period for this set of eggs was definitely established to be 19 days.
The next day the female attempted to brood the young continuously. One of the young, however, persisted in its attempts to break away from parental care in spite of the warning notes of its mother. In one instance the mother dragged the one young under her body until within reach of the unruly youngster, which was was quickly and violently tucked under her breast with something of an attitude of rebuff.
On the second day the young frequently appeared in the open and at such times often pecked at the mother's beak as if recognizing it to be the door of a well-filled cupboard. The young had not yet been fed, as they were still dependent on the yolk provided by the egg and stored in their bodies at the time of hatching. The female remained with the young throughout the day, whereas the male did not make his appearance until 8:50 in the evening. He announced his arrival with a sharp call as he landed on the roof. His call was immediately answered by the female, whereupon he made his way to the nest and without ceremony or delay delivered the first food received by the young. I was not prepared to see the male feed the young because the male of the preceding summer (another individual) never assisted in the care of the young. This striking difference in individual behavior emphasizes the point that it is not safe to generalize on observations of a single individual.
The next morning the female was brooding her young, and being accustomed to my daily presence she allowed me to reach under her breast to remove the young without exhibiting the least bit of fear. A female nesting on another roof when visited for the first time scooted away hurriedly, fluttered helplessly on the roof, enacting a perfect imitation of a crippled bird, a ruse to attract my attention away from her young. When I followed her she quickly flew away. On subsequent visits this bird stood her ground, elevated her wings in an upright position, and hissed at me in defiance of my approach.
The following notes are from the observations made of the young that were hatched on the high school roof the preceding year (1921). The female of that year was the same bird that nested there in 1922. The identity of the female was established by banding and also by a slight deformity of the maxilla, the tip of which was broken off. The males of the two broods were different individuals.
The young were fed during the early morning before sunrise and again in the evening after sunset. During the heat of the day, when the temperature frequently went soaring above 110o F., the young kept well concealed under the breast of the brooding bird in close contact to her abdominal air sacs. When the temperature was less torrid the young peeked their heads through the feathers and often came out entirely. At such times they sometimes amused themselves by picking at the mother's beak and rectal bristles. If the annoyance became too great the female would thrust her head beneath her breast. The young then proceeded to pick at the feathers of her crown and nape.
The female left the nest regularly about 8:30 p.m. (daylight saving time) to obtain food for herself and young. In the case of this brood the female delivered all the food required by the young. The food was delivered by the process of regurgitation. The beak of the female was thrust well into the large and widely distended mouth of the young when the transfer of food was made. After feeding, the adult brooded her young in the earlier stages of their development.
For the first three days the young remained near the spot where they had been hatched, but on the fourth day after a heavy rain they had moved to a slightly raised portion of the roof, which was free from excessive dampness. The female never left the young during a rain at this stage of their growth, even if it meant depriving them of food. The male regularly visited the roof early in the morning and again in the evening throughout the breeding season, but he was never seen to deliver food to the young. The male was usually stationed on the roof when the female was way and thus served as a watchdog in her absence. More than once he was called upon to chase away a strange nighthawk that had inadvertently alighted in his territory on the high school roof.
On the fifth day (June 29) the young had wandered to the southern end of the building where the shadow of the roof wall protected them from the direct rays of the burning sun. The heat during the middle of the day was frequently excessive. On July 7, when the young were 13 days old, a thermometer placed on the gravel of the roof registered 140o F. The heat was too much for one of the young, which succumbed and was found dead near the middle of the roof. Its fellow nestling, hidden in the shadow of the roof wall and behind a clay ventilating pipe, escaped death but was in a serious condition. A sponge soaked with cold water was placed near the youngster, whereupon it ignored its parent to enjoy the comfort provided by the cool sponge. This act probably aided the survival of the young nighthawk through the remainder of the record-breaking hot day.
As the nighthawk grew older he became very aggressive and pugnacious and never hesitated to pester his mother whenever he was hungry. At times he seemed mischievous. It was not a rare experience to see him crouch under his mother's breast and then by standing up quickly and rigidly topple his mother so that she was forced to extend her wings to keep from falling over. During the period of rapid growth of the wing feathers the youngster was continually extending and stretching his wings as if to relieve the uncomfortable feeling caused by growing pains.
When the young nighthawk was three weeks old he was able to make short flights from one place to another on the gravel roof. At this stage of his growth he had become so large that it was difficult for the female to cover him adequately while brooding. This was strikingly demonstrated on the evening of July 17, when he was 23 days old. The mother had left him alone on the roof while she was away on her regular evening search for food. It was so cool and damp that the young bird uttered notes that clearly indicated discomfort. I placed him in a woolen bag, and this, combined with the warmth of my hands, was very satisfying, as indicated by his change to notes of contentment. He remained there in comfort until his mother alighted on the roof and gave the characteristic call note, announcing supper. The little nighthawk struggled out of my bag and ran directly to his mother to be fed. After he was gorged with insects the female attempted to brood him, but to her apparent dismay he rushed back to the woolen bag, clearly recognizing that I could do a much better job at brooding.
On July 19, when the nighthawk was 25 days old, I discovered that he was no longer solely dependent on his parent for food. I found him busily engaged catching some white moths that had collected about a drain pipe of the roof. He was flying this way and that, catching the moths with great delight. As I sat there watching I chanced to pull a small handkerchief from my pocket, whereupon he dashed at the white object with the ferociousness of a tiger. Evidently to the nighthawk this was some giant moth large enough to provide for an entire meal.
The female now made frequent attempts to entice the young bird away from the roof by first offering food but flying away before it was delivered. The youngster would follow her in extended flights but invariably returned to the roof.
On July 24, when the bird was 30 days old, the female was photographed with the young for the last time. Thereafter she forsook her offspring for a roost in the nearby elm tree. She then visited the roof only for short intervals at feeding times. On each successive day the young bird took longer and longer flights, and each day I anticipated it would be my last opportunity to photograph and to observe him. Much to my delight he continued to return, seeming to enjoy my companionship.
On August 15 he left with the other nighthawks of the vicinity on their migration to the south. This unusual experience of having the bird return to the roof gave me an unprecedented opportunity to make a continuous set of daily observations and measurements of a nighthawk living under normal natural conditions up to the time it was 52 days of age. By this time the growth of the juvenal plumage was completed and exchanged in part for the first winter plumage.
Plumages.--On the first day the young are able to stand upright and are very active from the time of hatching. The eyes are open, iris bluish black; skin darkly pigmented darker above than below; bill "pale mouse gray"; tarsus and toes brownish drab. Down present on both dorsal and ventral parts of the body. Down of the ventral tracts pale gray shading to "pallid neutral gray" on the belly; chin gray, malar stripes and patch on the throat "dark mouse gray," approaching black. Upper parts mottled and marbled, made up of patches of pale gray and "dark mouse gray." In the region of the nape and scapulars the down has a distinct "pale olive-buff" tint. At the base of the beak the down has a tinge of buff. A circular area about the anus, the outer part of the shanks, and forearm have patches of darker colored down. Patterns of dark and white vary considerably in different young. The average length of the down on the various parts of the body varies as follows: crown 9, base of bill 4, region over eye 6, throat 12, belly 15, wing 11, and region of anus 8 millimeters.
On the third day the color of the bill has changed to a "deep neutral gray," and the tarsus and toes become a dusky drab. Down at the base of the beak, scapular region, and irregular patches of the back has faded from the colors present in the day-old chick to a "tilleul buff." Iris is now a clear brown instead of the bluish black of the freshly hatched chick.
At the age of 10 days the tarsus and toes are "deep Quaker drab," bill "dark neutral gray," eyelids "light neutral gray." Exposed portions of the eyes are noticeably greater. Down of the back much worn and matted down, the feather papillae in the region of the crown, wing coverts, scapulars, and rump now more conspicuous than the down. The tips of the feathers of the back are unsheathed and exhibit a black and cinnamon color. The color pattern of the back is completely lost since the appearance of the feather papillae and their unsheathed tips. The papillae of the tail feathers are only 8 millimeters long and as yet do not show through the down. The feather papillae of the head and tail are the last to unsheath.
In chicks 13 days old the "pinkish cinnamon" of the tips of the feathers of the dorsal tracts has faded to a "pinkish buff," and some of the feathers approach a "tilleul buff." Freshly unsheathed feathers of the crown are "pinkish cinnamon." Black markings have faded to a "fuscous-black" or "dusky neutral gray"; yellowing color of the breast feathers of the younger stages now faded to gray tinged with yellow. The juvenal plumage is rapidly replacing the natal down in all parts of the body. The yellowish-gray breast feathers are barred with "dusky neutral gray." As previously noted, one of the two birds dies from exposure to great heat at this time and the remaining descriptions are based on one bird.
At the age of 15 days the down is ragged in appearance but is still prominent on the breast, sides of the head, wing coverts, and region of the tail. The down is worn off the feathers in the region of the crown and scapulars. Feathers of all tracts of the juvenal plumage are partially unsheathed. When the young are handled there are numerous particles of the feather sheaths that scale off. The wings exhibit a marked development. The tips of the undertail coverts recently unsheathed are ivory colored. the down persisting at the tips of the feathers comes off with the slightest pull. The pupil of the eye appears bluish black and the iris has changed to a "Van Dyke brown."
When 17 days old the sixth primary has now proceeded with unsheathing so that the white patch is 13 millimeters in extent. Tarsus and toes are "blackish plumbeous," bill is a "dusky purplish gray," eyelids are "dark olive-gray"; otherwise the markings are similar to those of the 15-day-old bird.
When 20 days old a relatively small amount of down remains, but a few filaments can be seen on the tips of some of the crown feathers, sides of neck, and breast. Feathers of the wings are growing fast and are so heavy from the large amount of blood and large sheaths that the wings rest on the surface of the roof, the bird being unable to support them. The wings are frequently outstretched, apparently to relieve the uncomfortable sensation produced by rapid growth of the feathers. Bristlelike feathers now appear around the base of the beak. The fifth primary is grown so that the white patch is beginning to unsheath, and the base of the fourth primary shows white area on sheath, which is destined to form part of the white patch on the wing of the fully grown young. The white on the sixth primary made its first appearance in the 17-day-old chick.
At this age the crown is "dusky neutral gray" or black, the feathers tipped, barred, and spotted with "vinaceous-buff:; some of the tips approach "avellaneous." The feathers of the upper parts are dark, or dusky, neutral gray variously mottled with shades of gray and "avellaneous"; many of the feathers tipped with "pinkish buff." Auriculars "light cinnamon-buff" and black, tipped with lighter shades. Primaries and secondaries blackish warm gray, some of the feathers having an olivaceous-black appearance. All the remiges are tipped with "tilleul buff" or "vinaceous-buff." Some of the secondaries and inner primaries spotted with "vinaceous-buff." Coverts of primaries unspotted "blackish mouse gray" or black. Coverts of secondaries spotted with "tilleul buff" or "vinaceous-buff." Lesser wing coverts variously mottled with colors mentioned above. Feathers of the breast barred with "dark mouse gray" and shades of gray and white. Throat and chin with crescentic band of feathers, which are barred with dark gray and white, the white predominating. Band of feathers along the edge of mandible extending below the eyes to the auriculars "neutral gray" and marked with "vinaceous-buff." Under tail coverts "cartridge buff," narrowly barred with black. Middle of the belly a heavy mat of down. Eyelids "light olive-gray," tarsus deep metal gray.
At 25 days the down has been lost, except that of the middle of the belly and small patches on the legs above the heels.
At 28 days the colorings are about as described for the 20-day-old chick, but the colors are subdued and faded because of exposure to the intense sunlight. The down is now entirely replaced by the feathers of the juvenal plumage. Although the outer primaries are only partially unsheathed, the young bird is capable of long flights and frequently leaves the roof, but invariably returns.
At 30 days the secondaries and the primaries, except the outer ones, are now unsheathed. The barred feathers lining the wings are now in process of unsheathing.
At 35 days the prevailing color of the upper parts is olivaceous-black, glossed with greenish, but this base color is very much broken by irregular markings, spotting, and marbling of buffy gray and whitish; many of the larger spots approach a light vinaceous-buff, which is especially evident on the crown. Spots of the crown are larger than those of the back. The throat patch is now clear white, an indication of its sex.
At 40 days, all the primaries except the outer two are completely unsheathed. The white patch of the second to fifth unsheathed, that of the first is 11 millimeters.
The bird, although able to fly as well as an adult, returned to the roof each day and allowed me to make daily measurements and weighings without the least resistance. It never attempted to run or fly away when I approached to pick it up. When I arrived on the roof wall it gave a series of calls, which seems to be a sign of recognition. The bird placed before me in a natural sitting pose measured 187 millimeters from the tip of the bill to the tip of the wings. Distance from level of the crown to the board on which it is seated is 90 millimeters. Tip of tail to front of toe in natural position 150, and tip of folded wing to toe 165 millimeters.
The bird at this age is very active and vivacious and captures all its own food. It offers no difficulty for me to capture it for measurements and poses perfectly for photographs.
On Monday, August 15, there was a great flight and departure of nighthawks, and after that date the nighthawk was seen no more. Presumably it went southward on its migration. The bird was 52 days old, and I had an unexcelled opportunity to observe the bird up to the time of the completion of its growth.
The completed juvenal plumages in both sexes is similar to that of the adult female except that the throat patch is not so well defined; in some it is replaced by blackish and buffy bars. The barring of the underparts is more extensive and the coloration in general is paler than that of the adults. There are whitish tips on all the primaries.
The postnatal molt has already been described in detail under the account of the young. There is a partial molt that does not include the wings and tail in September. There is a partial or complete prenuptial molt in spring when the young attain the plumage of the adult. The adults have a complete postnuptial molt before they return for their nesting activities the following year. I have not been able to ascertain the time of the postnuptial molt.
Albinistic phases of plumage, in which there is an absence of dark pigment, may appear in any species of birds. W. A. Strother (1886) reports a perfect albino taken at Lynchburg, Va.
Food.--The nighthawk is insectivorous in its eating habits. Since the major part of the insects it destroys are destructive to useful vegetation or are otherwise adverse to human welfare, the nighthawk ranks high in the list of birds beneficial to man.
The nighthawk captures the insects chiefly during its flight. The birds sweep up in their capacious mouths all types of insects from large moths and beetles to the tiniest of flies and mosquitoes. Some of the stomachs examined have contained no less than 50 different species of insects, and some of the smaller insects are at times represented by thousands of individuals.
One of the most conspicuous elements of the food is flying ants. In the examination of 87 nighthawk stomachs, the United States Biological Survey reports that ants comprised nearly one-fourth of the total food eaten by the birds. In 24 of the stomachs the number of ants ranged from 200 to 1,800, and in all the stomachs examined there were not less than 20,000 ants (Beal, 1897). In the stomach of a nighthawk that met with accidental death at Brunswick, Maine, on August 20, 1925, there were 2,175 ants. The mass and weight of these insects were so great that they constituted a serious handicap and probably a factor in the bird's untimely ending. Charles Drury (1887) obtained a specimen in August that contained 320 insects, chiefly winged ants. W. L. McAtee (1926) found more than one hundred carpenter ants (Camponotus herculeanus) in one nighthawk stomach. In most all instances the ants captured are the mating winged individuals, which fly in immense swarms during the late summer. These ants are killed at a time when they are preparing to propagate their kind, and hence the death of every female means the destruction of thousands of the next generation.
According to examinations of the United States Biological Survey (Beal, McAtee, and Kalmbach, 1916) beetles comprised one-fifth of the food eaten by 87 nighthawks examined. May beetles, dung beetles, and others of the leaf-chafer family were in greatest numbers. Beal (1897) reported finding the remains of 34 May beetles (Phyllophaga) in a single nighthawk stomach, in another 23, and in a third 17. In the stomach contents of one specimen no less than 17 species of beetles were identified. Chester Lamb (1912) reports that all nighthawks collected by him had eaten enormous quantities of beetles. Thomas G. Gentry (1877) reports eight species of beetles in food examined by him. McAtee (1926) reports various leaf chafers, sawyers, wood borers, bark beetles, weevils, and plant lice in the food eaten by nighthawks in the course of his study of the relation of birds to woodlots in New York State. In the examination of hundreds of droppings of nighthawks obtained from various nesting sites chiefly at Brunswick, Maine, a large percentage of the identifiable remains consisted of parts of various species of beetles.
Nighthawks, especially in the Middle West, have been known to eat a considerable number of grasshoppers and locusts. According to Ernest Harold Baynes (1915) seven Nebraska specimens were found to have eaten 348 Rocky Mountain locusts; five specimens collected in Indiana reported by A. W. Butler (1898) had eaten 9 grasshoppers, 19 beetles, 23 Heteroptera, and 4 Neuroptera. B. H. Warren (1890) reported that grasshoppers were an important element of the food eaten by nighthawks collected in Pennsylvania. F. E. L. Beal (1897) states that one nighthawk contained the remains of 60 grasshoppers. A male killed on July 7, 1882, was reported by Everett Smith (1883) to have "an ichneumon fly, a black cricket, about twenty small grasshoppers, and many small hard insects" in its crop.
Flies, plant lice, and mosquitoes frequently form an important element of the food of the nighthawk. A nighthawk examined by the Biological Survey had eaten more than 300 mosquitoes, and E. H. Forbush (1907) reports finding 500 mosquitoes in the stomach of one bird. McAtee (1926) reports that he found 650 plant lice in the stomach of a single nighthawk. Phoebe Knappen (1934) found stone flies in 21 nighthawks. The insects were chiefly adults but also a few larvae, nymphs, and eggs were present.
In the South various observers have noted that the nighthawk is an important factor in the control of the cotton-boll weevil. F. H. Herrick (1901) writes of a nighthawk that had been feeding on fireflies; the wide open mouth of an adult observed feeding its young was brilliantly illuminated like a spacious apartment all aglow with electricity. F. H. Carpenter (1886) relates a unique experience with nighthawks that darted at the artificial flies on his line when he was casting for trout. It is not an unusual experience to see nighthawks after dusk flying about electric lights of city streets (Knowlton, 1896) or about campfires of remote districts where they capture myriads of insects attracted by the lights.
During the migration nighthawks frequently fly near the ground and at such times may take advantage of any insects that appear in their path. During an afternoon late in August I observed a flight of several hundred nighthawks near Urbana, Ill. As I sat in a car alongside a large meadow I noticed that the birds were ravenously feasting on grasshoppers. Some of the birds lingered long enough to capture half a dozen of the insects before passing on to make place for other nighthawks in the migrating procession. A. Dawes DuBois, of Excelsior, Minn., relates a similar experience he had in the vicinity of Salt Creek, Logan County, Ill., as follows: "At dusk on the evening of May 22, 1913, as I walked along a cloverfield, we witnessed an assemblage of nighthawks in pursuit of low-flying insects. They skimmed over the clover like swallows; and their dusky forms were so numerous that they seemed to be weaving an intricate pattern in the gray twilight. They were so intent on their bountiful repast that they paid no heed to our presence, but sometimes darted past us only a few feet away."
Nighthawks not only capture food on the wing, but they also have been observed to drink, in the manner of swallows, as they skim near the surface of the water of lakes and streams. F. Stephens (1913) observed a nighthawk drinking from a watering trough. This bird dropped its lower mandible into the water, rippling the surface of the water as it passed along. A. Dawes DuBois writes of the following experience he had at Springfield, Ill., on July 29, 1923: "Mr. R. B. Horsfall and I were walking along the margin of a small pond when a nighthawk swooped down, touched the surface of the water and rose again; but we could not tell whether it was scooping up a floating insect or a drink of water."
The loud piercing calls uttered by the nighthawk during flight are simple yet, like all bird notes, extremely difficult to represent in written words so as to enable a reader unfamiliar with them to gain a clear conception of their character and quality. This fact is at once emphasized if we compare the interpretations of a few of the many authors who have attempted a written version of its calls. For example, to C. A. Abbott (1914) it sounds like a "grating 'beedz, beedz,'" and to Charles Bendire (1895) it is a querulous and a squeaky note resembling "aek-aek, aek-aek" or "speek-speek, speek-speek." W. E. Grover describes this note as a sharp "mueike"' and E. H. Forbush (1907) states that "the note is s-k-i-r-k or s-c-a-i-p-e, a little like the call of Wilson's snipe--rather a startling squeak when heard close at hand." W. L. Dawson (1903) interprets the note as "mizard, mizard," and E. H. Eaton (1914) describes it as a "loud nasal 'peent, peent.'" N. S. Goss (1891) writes that its voice is a "squeak" or a "pe-up" note, and Arkansas Hoosier (1890) states that "the note is best produced by speaking the word 'beard' in a whisper." To G. R. Mayfield (1921) the call is a shrill "B-e-e-r-b" and to H. Nehrling it is "Brirrr-brirrr." H. Tullsen (1911) interprets it as a sharp penetrating "Spe-eak," and H. H. Bailey (1913) thinks it sounds like "Queek-queek."
There was probably only the slightest variation in the notes of the different nighthawks as heard by the authors mentioned above, yet how strikingly different are the interpretations as represented in the written or printed words. The note described above is the one most frequently heard, and it is uttered independently of the seasons. It is the note that announces the arrival of the nighthawk in spring, and it is the call uttered at the time nighthawks are congregating in fall in preparation for their departure to the south. I have been unable to ascertain whether this call is heard at their winter home in South America.
Frequently, during the courtship season, the males in their competition for a mate vigorously pursue each other. At such times both birds utter a series of sharply accented calls recorded in my field notes as resembling Dick-a-dick-a-dick-dick-dick-dick-dick, given in rapid succession.
There is another note of the nighthawk very different in character, an aeolian sound, produced by the rush of air through the primaries of the wings at the termination of the extraordinary downward plunge executed during the courtship season. In order to see this performance and to hear this peculiar and unique note to the best advantage it is necessary to visit the vicinity of the nesting site. Alexander Wilson (1828) described this note as a "loud booming" sound very much resembling that produced by blowing strongly into the bunghole of an empty hogshead." E. H. Eaton (1914) offers a modification of Wilson's description in stating that the note is like that produced "by blowing across an empty bottle." T. G. Gentry (1877) describes it as a sound resembling that "produced by a tense cord set in vibration by a sudden gust of wind." T. Jasper (1878) states that it is a hollow whir like the rapid turning of a spinning wheel, and F. A. Hartman (1914) describes it as a "guttural 'woof.'" The note reminds W. A. Stearns (1883) of the sound produced by a bellowing bull. In my field notes I have described this note as a muffled wr-r, r, r, r, r-oonk, but sometimes more nearly approaching sw-r, r, r, r-ooonk, the last syllable decidedly accented and produced with great resonance. There is nothing about this note suggesting an explosive boom or bellowing.
It has long ago been well established that this peculiar note is not a vocal sound but one produced by the vibration of the primaries. As keen an observer as Alexander Wilson (1828) stated that it is "produced by the sudden expansion of his capacious mouth." Others shared Wilson's view or thought that it was a sound produced by the syrinx. After one has observed the performance it can be readily understood how such an erroneous interpretation was made by the earlier observers. The plunge takes place so quickly that it is only by repeated observations made under the most favorable conditions that the observer is convinced that the primaries are involved. Audubon (1840) was the first to arrive at a correct explanation. He writes that the source of the singular noise is "the concussion caused, at the time the bird passes the centre of its plunge by the new position of its wings, which are now brought almost instantly to the wind, like the sails of a ship suddenly thrown back." This observation with variation of its details has been made by numerous subsequent observers. J. B. Canfield (1902) gives a description of the performance as follows: "He suddenly paused and came soaring toward me like an arrow. About fifty feet in front of me his wings were lowered below his body, throwing them forward with the flight feathers spread wide apart. . . . His speed was so great that the flight feathers vibrated like a loosely-stretched rubber band when snapped with the fingers. This performance was repeated in front, back, and beside me twelve times in all, never more than fifty feet away, and as near as fifteen. In all cases the wings were in the same position, and his mouth never open."
F. A. Hartman (1914) writes, "It is very evident that the mouth plays no part, otherwise the sound would be produced at other times [than on the downward glide]. . . . The bird threw its wings far to the front at the end of his downward glide, so that the uppermost quill feathers were pointed exactly in the direction of his glide. Going at such headlong speed, these quill feathers, when thrown edgewise to the air vibrated strongly, causing the 'woof.'" Alden H. Miller (1925) while at Camp Lewis, Wash., during June and July succeeded in attracting nighthawks within 10 feet of himself by merely waving his hat in the air. He noticed that if the wings, during the downward plunge, were held in the upturned V-shaped position, a normal pose when soaring, no boom was heard, but when the wings were bent downward near the end of the dive the boom sound was produced. The intensity of the sound, according to Mr. Miller, is more or less proportional to the speed attained. The main explosive boom seems to be preceded by a brief, lesser vibrating sound, which bursts forth into the full bellow. Both parts seem to have a distinct element of pitch, but the latter part is lower, with greater resonance and depth of quality.
The sound produced by the wings described above is a part of the courtship performance and is usually produced near the nesting site. After the young no longer require the constant attention of both parents, the male loses the glamour of romance and performs less frequently and soon after ceases almost entirely until the courtship season of another year. However, birds migrating in August sometimes "boom."
Another note associated with the courtship season is a guttural call uttered only when the male is at rest and in the presence of the female. It may be described as an oft repeated auk, auk, auk or awk, awk, awk. This note is produced by the syrinx, but as it is uttered the bill is tightly closed and the gular membrane is tightly distended each time the note is produced. The distention is caused by the expulsion of air from the respiratory system. The distended membrane, although feathered, acts as a resonator and modifies the note, giving it a peculiar quality. Such a mechanism is present in other birds. It is especially highly developed in the prairie chicken, in which large lateral vocal sacs are present that give the "booming" notes of this grouse great carrying power.
The notes of the female nighthawk are simple calls uttered in response to those of the male or of the young. She may utter a purring, pacifying note when brooding the young, but often these notes are so weak that they cannot be heard by the observer unless he is stationed very near in a blind.
Game.--Today we do not think of the nighthawk as a game bird, yet 60 years ago large numbers of them were killed by gunners and sportsmen, especially in the southern states. M. G. Elzey, writing on September 18, 1876, stated: "Bull-bats (nighthawks) are the best of the minor game of this country for sport or table; have been very abundant and in superb condition here (Blacksburg, Virginia) for the past two weeks. I have killed several hundred. On one occasion took out 28 cartridges and brought in 23 birds besides 2 which fell out of bounds and were recovered by boys. Killed 17 in succession. The bats are quite as fat and better game than the reed birds." Dr. E. Sterling (1885) wrote: "Their rapid and irregular flight makes them a difficult mark for the young sportsman to practice on, as he never fails to make a target of them when the opportunity offers. I can now understand the object for which this bird was created." Dr. F. M. Chapman (1888), writing of conditions at Gainesville, Fla., stated, "'Bat' shooting is here a popular pastime, great numbers being killed for food, and in August, when the birds have gathered in flocks, favorite fields may be occupied at nightfall by as many as a dozen shooters." Stockard (1905) lamented the fact that the birds "are foolishly slaughtered by pseudo-sportsmen who shoot them merely to watch the bird's graceful fall or to improve their skill as marksmen."
The practice of killing nighthawks was stopped through laws and by educational methods initiated by the National Association of Audubon Societies. William Dutcher (1902), in writing of conditions in Florida, stated, "It is believed, on very satisfactory evidence, that the new law has stopped to a large degree the disgraceful practice of shooting 'bull-bats' or Nighthawks (Chordeiles virginianus) for sport." Bird-Lore for September-October 1903 published the following note: "The Nighthawk, or Bullbat, has been so long considered a legitimate target for shotgun practice, in the south, that a report of prosecution for killing these birds at Greensboro, North Carolina, marks a new era of bird protection in our southern states."
Enemies.--The greatest enemy of the nighthawk has been man. In the past great numbers of the birds were killed for food and often for mere sport or for satisfying a lust for killing. This was especially true in the southern states, where the birds were slaughtered during the great flights of the annual migrations.
Nighthawks nesting on the ground are subject to the same enemies experienced by other species of ground-nesting bids. Nighthawks nesting on roofs are usually free from such molestation, but Albert F. Ganier informs me that he has known of sparrow hawks invading the cities and preying upon the nighthawks, especially the young. Cats and dogs become enemies of the city dwellers in the event the young leave the nest prematurely and land on the streets below.
Nighthawks have a remarkable protective coloration and have
developed methods of deception such as imitating a wounded
individual when an enemy approaches the nesting site. At times
they assume an attitude of aggression; i.e., raising their
elongated wings in a vertical position and hissing in defiance at
Common Nighthawk* Chordeiles minor [Eastern Nighthawk]
*Original Source: Bent, Arthur Cleveland. 1940. Smithsonian Institution United States National Museum Bulletin 176: 206-234. United States Government Printing Office