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 favorite
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 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, or 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, in 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 for 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 the 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 Androscoggin 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 flash light.
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 the 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 taken 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
to the nest.
8:50 p. m. The female returns to the nest after being away only
three minutes. The male was quiet 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 130° F., although it was only
98° 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 temperature sometimes dropped as low as 45° F. If the
female should leave her eggs when the temperature rises as high as
130° F. the embryos inside of 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 heard 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.