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Blue-gray
Gnatcatcher
Polioptila caerulea
Contributed by Francis Marion Weston
[Published in 1949:
Smithsonian Institution United States National Museum Bulletin
196: 344-364]
Our acquaintance with a new bird dates, it seems to me, not
from the moment we learn to identify it in the field but rather
from the first time we really have a glimpse of its
"personality." Thus, my "first" blue-gray
gnatcatcher was certainly not the one my ornithological mentor
first pointed out to me, but another that came along months later,
flitted to a bush within arm's length of where I stood and,
between snatches at insects too small for me to see even at that
short distance, spent several minutes looking me over.
It was upon the foundation laid in those few minutes that I
have built whatever else I may have learned about the gnatcatcher.
In the course of writing these pages, the memory of that first
meeting has come back to me many times, almost with the clarity of
a visual picture, and I feel that I am telling of the later
adventures of one little bird rather than of the habits of its
myriad kin.
The habitat of the blue-gray gnatcatcher evidently varies
materially in different parts of its range. In the far South,
where it is resident, it is common and widely distributed in the
nesting season, occurring regularly even in the residential
(wooded) sections of the cities and towns, as well as in all
forested areas, wooded swamps, pine lands with an undergrowth of
scrub oak, pecan and citrus groves--in fact, everywhere where
there are trees suitable for nest sites. Farther north, it is
characterized as being a bird of the watercourses and the timbered
swamps, spending most of its time in the tops of the tallest
trees. An interesting variation is noted from the "great open
spaces" of Kansas, where N. S. Goss (1891) wrote of its being
"as much at home in the shrubby bushes on the hillsides, or
the mesquite growths on the plains, as within the treetops of the
heavily-timbered bottom lands."
Spring.--A few years ago it would
have taken a whole paragraph to describe the spring arrival of the
blue-gray gnatcatcher on its breeding grounds, for its movement
from winter quarters in the southern United States and the Tropics
differs from the familiar wavelike rush of the warblers. Today we
need but a single word of the military parlance that has become
part of our everyday speech: Infiltration. Yesterday, the
gnatcatchers were not here; today, they, are; and we are always a
bit surprised when we discover them. Early in March they are on
the move from southern Florida; by the last of the month they are
halfway on their course across the country; and mid-April finds
them at the northern limits of their normal breeding range.
Courtship.--For a week or two
after their arrival, they are still silent and retiring in habit;
then suddenly they all seem to come to life and are ready to
resume that all-absorbing function of all living
things--reproduction.
In common with many of the other small birds, the gnatcatcher
seems to have no well-marked courtship ritual. We note the
unrestrained animation of the male birds, see their frequent
bloodless combats, hear their ceaseless singing and
chattering--then, after a surprisingly short interval, we find
that mates have been selected and the serious business of
nest-building is under way.
The song of the male gnatcatcher, even at the peak of his
spring animation, is scarcely louder than a whisper, and it is
interesting to note the opinion of our ablest interpreter of small
bird actions, Mrs. Margaret Morse Nice (1932), who finds that the
male of this species, unlike louder-voiced birds, "does not
sing to proclaim his territory; perhaps the spee which is
constantly given by both birds serves this purpose."
Nesting.--More than with most
species of small birds, the attention and interest of the observer
center about the nesting habits of the blue-gray gnatcatcher
because of the great beauty of its nest. This nest should be even
better known than its miniature counterpart, the nest of the
ruby-throated hummingbird, for by virtue of its larger size and
consequent better visibility it can be found much the more readily
of the two--yet it seems to have been entirely overlooked by the
general public and is known only to ornithologists.
The general situation of the nest in the extremes of the
breeding range of the species is decidedly different. In the
southern end of the range nests can be found almost everywhere
that trees grow--from the residential sections of the cities to
the heart of the great river swamps--but farther north they occur
principally along watercourses and in timbered swamp areas.
The height of the nest above ground varies from a few feet to
70 or 80. By far the greater number-- those seen by human
observers, at any rate--are less than 25 feet up; but this may not
represent true distribution in height for, as G. A. Petrides
points out, "the noisiness and lack of suspicion of the birds
about the nest probably enabled the low ones to be located more
easily." I suspect that the reported heights of the very high
nests were estimated rather than measured, but there are
dependable figures available for many low ones. I have found some
of these low nests myself: one just 4 feet from the ground near
the end of a low-sweeping branch of a pecan tree; another within
camera tripod reach of the ground (not more than 5 feet up) in a
small lemon tree; and several that were between 5 and 7 feet up in
small scrub oaks in open pine woods. Angus McKinnon (1908)
mentioned one in northern Florida that was "in a small oak
only about three and one-half feet from the ground." The
lowest figure of all is given in a recent letter from R. A.
Hallman of Panama City, Fla., who describes a "typical
Gnatcatcher nest, placed in the upright fork of a small scrub oak
bush", which was "by actual measurement 38 inches. .
.from the ground to the top of the nest."
The nest is usually saddled on a horizontal limb 1 to 2 inches
in diameter--occasionally on a larger one--but it is often placed
in a fork formed by an upright branch and a horizontal or slanting
one, the lower branch furnishing the foundation and the upright
lending side support. An interesting variation was reported by J.
J. Murray (1934), who described a nest near Lexington, Va., that
"was not saddled on a limb, but set between [sic]
three small forks of an upright crotch, in the manner of the nests
of the Yellow Warbler and Redstart."
An attempt to compile from the literature a list of the trees
selected by the gnatcatcher for nesting sites resulted in a
collection that reads like a catalog of the silviflora of eastern
North America. It seems that this species is willing to use any
tree in its habitat that provides limbs of the right size and
conformation. In the North, where the bird is uncommon or rare, no
generalization as to preference can be hazarded. In the South,
where it is common to abundant, some local tendencies are noted
but these vary widely in different sections. A. T. Wayne (1910)
found that, in coastal South Carolina, the gnatcatcher prefers the
live oak (Quercus virginiana) "because nesting
material is plentiful." S. A. Grimes (1928), writing from
Jacksonville, Fla., stated that "oddly, or not, the pine is
the tree most commonly chosen for the nest site." In his
experience "the pines (at least two varieties) have been
selected. . .oftener than all other trees combined." That
choice could hardly have been influenced by availability of
nesting material. In extreme western Florida and southern Alabama
I have found more nests in scrub oaks (principally Quercus
catesbaei and Q. cinerea) growing in open pine woods
than in any other trees, and I have never seen a nest in a pine.
Location in a tree with lichen-covered bark provides the ultimate
in concealment for a lichen-covered nest, but this correlation
does not seem to be a factor in the choice of a nest site. The
preference for pines in the Jacksonville area, as cited by Grimes,
is a case in point, and I have seen nests in citrus trees, pecan
trees, and cypresses where little or no lichen growth was present.
Yet the nest, even in other than its optimum surroundings, is
always difficult to see and is seldom found except as "given
away" by its owners.
If it were possible to extract a composite or average of all
the published descriptions of the nest of the gnatcatcher--and the
wording of most of them is monotonously similar--the result would
be something like this: A beautiful, cup-shaped nest, compactly
built of plant down and similar materials bound together with
insect silk and spider web and covered externally with bits of
lichen. Materials listed seem to include every kind of soft plant
fiber found in the region where the subject nest was located. Many
writers use the general terms "plant down" and
"fleecy plant substances," but a few particularize with
"sycamore fuzz," "leaf down from the under surfaces
of leaves," "dandelion and thistle down," and
"dried blossoms." Fibrous materials that enter into the
lining of nests include fine strips of bark, fine grasses,
tendrils, feathers, and horsehair. A. T. Wayne (1910) collected
several nests that were "profusely lined with feathers."
W. P. Proctor mentions having seen a gnatcatcher in northern
Florida "picking the petals from dewberry blossoms [Rubus
trivialis] for its nest."
I was interested to discover what degree of availability
determines the selection of material for a particular nest. I had
an old nest, a mantel decoration much the worse for dust and age,
of which I knew the original location--it had been taken from a
point about 20 feet up in a medium-sized live oak that grew on the
edge of a highway right-of-way where it entered a wooded swamp.
Pulling the nest to pieces, I found it to be composed largely of
oak catkins felted together with plumed seeds and a kinky plant
fiber, buff in color, that I could not name at the time. Scattered
though the mass were a few small pieces of what appeared to be
"sheet" spider web or fragments of cocoons, but there
was no vestige (even under a strong hand lens) of the insect silk
or spider web that had presumably been used to bind the outer
covering of lichens to the body of the nest. Actually, there was
no longer need for a mechanical binder since the lichens had
attached themselves firmly to their new foundation. The inner cup
of the nest was a felted structure, readily separable from the
base and from the outer, lichen-covered sheathing. It had been
shaped by a few stiff, wirelike grasses (unidentified) disposed
though the felted material almost like the reinforcing bars in an
engineer's concrete structure, and the felting was composed
entirely of the plumed seeds and the kinky fiber and contained no
catkins. Upon visiting the original site at the usual season of
nest building, I found (as I knew I should) that the oak catkins
and the lichens were obtainable in unlimited quantity within
inches of the spot where the nest had been built. The plumed seeds
proved to be from one of the broom grasses (Andropogon
sp.), a small dried patch of which, still bearing a few seeds late
in the season, was within10 yards of the base of the nest
tree--and I could find no more within a hundred yards in any
direction. The kinky buff fiber was discovered in inexhaustible
abundance along both sides of the right-of-way: it was the stem
"wool" of the cinnamon fern (Osmunda cinnamomea).
Measurements of two nests were kindly furnished by W. P.
Proctor. One was: outside, 2 inches diameter by 2 1/2 deep;
inside, 1 1/4 inches diameter by l 1/4 deep. The other measured:
outside, 2 1/2 inches diameter by 2 1.4 deep; inside, 1 1/4 inches
diameter by 1 3/8 deep. The striking feature of both these sets of
figures is the difference between the inner and outer depths--l
1/4 inches in the first nest and 7/8 inch in the second. These
differences represent the thickness of the foundations of the
nests, the thickness of the pads of resilient, closely felted
material between the weight of the contents and the surface of the
supporting branch. It is not unlikely that the remarkable tenacity
of these tiny nests under stresses of weather buffeting and family
struggles resides in the elasticity of their thick, resilient
foundations. A moment's consideration of the proportions of the
deep cup of the nest-- 1 1/4 by 1 1/4 inches--and of the slim
length of the little bird that must crowd itself into these narrow
confines explains why the incubating gnatcatcher can assume no
other posture than with bill and tail pointing straight upward.
Most observers agree that both sexes work at the construction
of the nest, and my experience in northern Florida is that they
share this labor fairly equally. W. E. C. Todd (1940) stated that,
in Pennsylvania, the male never assists in nest building but that
he ''always remains near at hand and takes a great interest in the
work.'' W. P. Proctor, reporting from southern Michigan, writes
that in one instance of the three observed by him, the female
alone did the building, and that on one shared task the female did
more than the male. Aretas A. Saunders, however, writing from
central Alabama, finds that where there is an unequal division of
labor the male bears the heavier burden, and also that the male is
a more persistent worker than his mate and that he is less
sensitive to interference by human intrusion. He cites an instance
of one male bird that was seen to bring nesting material five
times in six minutes. Slower than this high-speed worker was a
building pair reported by Mrs. Nice (1931), who counted 27 trips
to the nest with material in an hour. It always gives an observer
a start, when he is watching nest construction and has seen
material brought in and placed in position to, have a bird come in
with a seemingly empty bill, yet work as diligently at the
structure as before. It is more in keeping with the known industry
of this species to account for this apparently wasteful gesture as
the placing of invisible lengths of spider web rather than as mere
''boondoggling."
The length of time required for nest construction is subject to
extreme and inexplicable variation. W. E. C. Todd (1940) stated
that it requires between one and two weeks of constant labor to
complete a nest. But Edward R. Ford writes of a nest that he saw
under construction from the very beginning that, after only three
days, "appeared, from the ground, to be completed."
Perhaps the important factor in this variation is the size of the
"building crew"--one bird alone, or both birds.
A practice, apparently peculiar to the gnatcatcher, and one
that has been commented upon by almost every observer familiar
with its ways, is its habit of tearing up a completed or partly
built nest and re-using the materials to build a new nest a short
distance away. L. L. Hargrave (1933) has collected and summarized
a number of published accounts of this peculiarity, and he
concludes that nests are abandoned because of a change of
conditions that renders the first site untenable or at least no
longer desirable. He cites one case where a pair of green herons
started their nest close to a still unfinished gnatcatcher's nest,
and other cases where human interference was probably the
determining factor in causing abandonment. A nest, once abandoned,
immediately becomes the most convenient source of material for
another structure. This use of an existing nest is all the more
readily understandable when the extremely seasonal nature of
desirable nesting material is considered. In the nest that I
described earlier in this section, the predominating
materials--oak catkins and "wool" from the cinnamon
fern--are obtainable in quantity only over a short period. After
this critical period, existing nests are the sole source of
supply. Besides the nests that are moved by their constructors in
extension of the original building program, I have known nests in
which broods had been successfully reared to be torn up and
carried off by gnatcatchers, but whether the "wrecking
crew" and the original owners were the same or not, I am
unable to state.
Nest-building in many parts of the gnatcatcher's range precedes
egg-laying by 10 days or two weeks. C. K. Lloyd (1932) attempted
to account for the need of this interval in the more northern
sections by stating that the birds "nest early. . .and do not
deposit eggs until the trees are well leafed out," but he
gave no reason for the practice of "nesting early." In
northern Florida, where many nests are built in evergreen trees
and where most of the deciduous trees are in full leaf at the time
of nest-building, this explanation does not hold good, yet the
same length of time elapses between the completion of the nest and
the laying of the first egg as in the North. It seems to me that
nest-building is best accomplished at the time that the favored
nesting material is obtainable in greatest abundance, even though
that does not coincide with egg-laying time. Thus, in northern
Florida, nest-building takes place early in April when oak catkins
and fern "wool" are available with the least labor of
search, but eggs are seldom laid before the third week of April.
Eggs.--[AUTHOR'S NOTE: Four or five
tiny eggs usually constitute the set for the blue-gray
gnatcatcher, seldom more or fewer. They are ovate or short-ovate
and have little or no gloss. The ground color is pale blue or
bluish white. They are rather sparingly and more or less evenly
covered with small spots or fine dots of reddish brown, or darker
browns; rarely there are a few very small blotches; sometimes the
markings are concentrated in a ring around the large end; and very
rarely an egg is almost immaculate.
The measurements of 50 eggs average 14.5 by 11.2 millimeters;
the eggs showing the four extremes measure 15.5 by 11.2,
15.2 by 14.7, 13.2 by 11.2, and 15.2 by 10.7
millimeters.]
Young.--Little has been written
about the nest life of the blue-gray gnatcatcher, and my own notes
are peculiarly deficient in this respect. Out of the many
gnatcatcher nests that I have seen, I find that I have not
followed the history of a single one completely through any one
phase of its development.
Incubation is said to require about
thirteen days from the laying of the last egg. G. A. Petrides,
writing of a nest near Washington, D. C., found "day-old
young" on May 21 in a nest where the last egg of the set had
been laid on May 8. William Palmer (1906) stated that, during
incubation, the female parent "rarely leaves the nest"
and is fed there by the male, the inference being that he does not
share in the duties of incubation. On the other hand, Mrs. Nice
(1932) remarked the close cooperation between the parents during
incubation and stated that they relieve each other on duty at
short intervals (15 to 40 minutes) and that the eggs are not left
uncovered for more than a minute at a time. W. P. Proctor, of
Benton Harbor, Mich., coordinates these apparently irreconcilable
statements when he writes: "At some nests, both birds sit on
the eggs; at others, the female alone sits. Where the birds take
turns, one usually sits from 15 to 25 minutes. At a nest where the
female alone sat, there was no regularity; she was off anywhere
from an instant to 15 minutes, and once. . .26 minutes."
Care of the young is characterized by the usual intense
activity of this species, both parents sharing the duties of
feeding and brooding the young. So unsuspicious, or so
preoccupied, are they at this time that they completely ignore
human proximity and fly directly to the nest with food. Added to
this "dead give away," the growing young in the nest
soon become very noisy, so the finding of nests at this stage of
development is an easy matter for even an inexperienced observer.
In the experiment to be described later in the section "Behavior,"
Maurice Brooks (1933) stated that a feature of the feeding of the
young "was the extreme frequency"--43 feedings in
20 minutes, 34 by the female, 9 by the male. This unequal division
of labor does not obtain, I believe, under natural conditions for,
although I do not have notes to verify it, my recollection is that
the male visits the nest with food almost or quite as frequently
as does the female.
Food brought to the young consists exclusively of animal
matter, mostly insects; but so tiny are the separate items that an
observer at a distance of only a few feet can seldom identify
them. Sometimes larger prey is brought in, large enough according
to W. P. Proctor, for the parent to have to "pound it on a
limb" before offering it to the young.
The normal span of nest life is 10 to 12 days. S. A. Grimes
(1932) wrote of a set of four eggs in the Jacksonville area that
"hatched May 10 or 11, and the young left the nest on the
21st." G. A. Petrides gives a period of 11 or 12 days for the
brood that he reported as having hatched on May 20, since they
were "apparently ready to leave the nest on the evening of
May 31." Beryl T. Mounts (1922) reported a nest near Macon,
Ga., in which the eggs hatched on or about May 16 and the young
left the nest on May 26.
E. H. Forbush (1929) wrote that, in the greater part of their
range, gnatcatchers rear but a single brood in a season but that
two broods are normal in the far South. However, S. A. Grimes
(1928), one of the most ardent and capable observers of nesting,
stated that, in the Jacksonville region, this species "raises
only one brood in a season." Though I cannot make a positive
statement on this subject, since I have never banded or otherwise
marked gnatcatchers for individual identification, I believe that
some of the late nests I have found were true second nestings and
not second attempts by birds that had failed the first time.
Taking April 24 as a median date for complete sets of eggs in
northern Florida, a nest that I found just being completed on May
25, 1930, may or may not have been a second attempt by a pair that
had lost their first nest; but a nest just started on June 1,
1941, in which a brood was later successfully reared, seems to me
to represent a true second nesting; and there can hardly be any
doubt that a brood that I saw just out of the nest on August 8,
1926, comes in this category.
Plumages.--[AUTHOR'S NOTE: The
young gnatcatcher in juvenal plumage is much like the adult
female, both sexes being alike and lacking the black forehead. An
incomplete postjuvenal molt occurs in July and August, which
involves the contour plumage and the wing coverts, but not the
rest of the wings or the tail. This produces a first winter
plumage, which is similar to the previous plumage but more washed
with brownish on the back and sides. The first nuptial plumage is
acquired in February by a limited molt of the feathers of the
forehead, throat, and chin, when the black frontal band of the
male is acquired, the upper parts become bluer and the young bird
is now in adult plumage. A complete postnuptial molt occurs in
July and August. Young males lack the black frontal band during
the first fall and winter, and the females never have it.]
Food.--In common with most of the
other very small birds (though not the hummingbirds) of eastern
United States, the blue-gray gnatcatcher eats very little if any
vegetable food; and, by virtue of its fondness for some of the
insects most harmful to man's interests, it is considered an
entirely beneficial species. A. H. Howell (1924) quoted the
findings of Judd's analyses of stomach contents and cited
particularly "longicorn beetles, jointworm flies,
caddis-flies and several. . .unidentified Diptera." He stated
also that the gnatcatcher had been seen in Alabama "feeding
on cotton leaf worms." E. H. Forbush (1929) added to this,
"locusts. . .gnats, . . .ants and other hymenoptera,
wood-boring beetles, weevils and spiders." A. A. Allen (1929)
summed up many important items of the gnatcatcher's diet under the
comprehensive term, "defoliating insects." It is not
unlikely that a stomach analysis of Florida and Texas specimens
taken in the citrus groves, one of the favorite haunts of this
species, would disclose the presence of some of the citrus pests.
Winter food of the birds that remain within our borders
probably consists largely of insect eggs and pupae, the known prey
of the chickadees and kinglets with which the gnatcatcher
associates at that season.
Food-table offerings seem seldom to attract this species; in
fact, I am able to find but a single instance of it, and that in
winter. Mrs. Andrew L. Whigham, who maintains an all-year feeding
station in her garden in extreme western Florida, writes: "In
January and February, 1933, for six or eight weeks, two of these
birds used our feed shelves. They ate the inevitable cornbread [a
saltless recipe of Mrs. Whigham's, baked in quantity for the birds
and proven to be as attractive to most species as cracked
sunflower seeds] and the commercial mockingbird food mixed with
grated carrot."
Behavior.--The gnatcatcher is a
little bird of intense activity; active, not with the methodical
continuity of the brown creeper, but with an irrepressible
vivacity of its own in all phases of its life cycle--feeding,
nesting, care of its young--at all times, in fact, except during
the enforced inertia of incubation.
In defense of its nest, the gnatcatcher's small size places it
at a disadvantage in competition with larger species, for it seems
not to possess the "driving power" of the even smaller
hummingbirds, though it lacks nothing in either bravery or
initiative when occasion demands (see section "Enemies"
for a special case of nest robbery by blue jays). Its attitude
toward human invasion of the sacred precinct of the nest shows
wide individual variation. On the few occasions when I have
approached closely to a gnatcatcher's nest, my presence always
caused great excitement, which was evidenced by noisy protests but
never resulted in a direct attack. S. A. Grimes (1928) found the
brooding gnatcatcher very tame, and on several occasions he
"climbed to within five or six feet of a sitting bird without
causing it to leave the nest, or when it did it usually returned
before I could get the camera set up for photographing." In
sharp contrast to this, the same writer (1932) described an attack
made upon him while he was photographing a nest, when the male
gnatcatcher actually "struck the writer several times on the
head and once in the eye," this last blow incapacitating him
completely for a time. Maurice Brooks (1933) tamed a pair of
gnatcatchers by making gradual advances toward the nest during the
period of incubation until, after the young had hatched, he and
his family could come within 2 or 3 feet of the nest without
interrupting the feeding schedule. Finally he cut off the nest
branch and lowered it for easier observation, still without
apparently disturbing the parent birds. His next move was to cup
his hands loosely about the nest in an attempt to compel the
parent birds to alight on the hands. This intimacy was more than
the birds would stand and the result was surprising as the female
immediately attacked viciously and repeatedly. Amicable relations
were later reestablished, and the female did occasionally actually
alight upon the experimenter's hands, but even then she would
without warning "sometimes take time out to attack." All
attacks were made by the female.
Except during courtship and in defense of its nest, the
gnatcatcher has never seemed to me to be pugnacious. Certainly, in
its winter association with chickadees, titmice, and kinglets, it
shows no tendency to harass or tease; so Alexander F. Skutch's
note on the wintering birds in Guatemala comes as a surprise when
he writes that "the adult males do not seem to get along
together." He cites as an instance: "On November 12,
1934, while following a large flock of small birds through open
woods near Huehuetenango, I noticed of a sudden two blue-gray
gnatcatchers in the oak tree in front of me. Upon finding
themselves face to face, they became excited and attempted to
sing; but at this season their voices were rusty from disuse, and
their notes came thin and wheezy. Flying at each other, they
clashed in midair; but the momentary affray was without
consequence. After the first onset, they separated. From their
attempts to sing, I feel sure that these birds were males. I have
witnessed similar behavior--often with singing--on the part of
other small birds which are solitary during the winter, when two
of the kind come together."
The flight of the gnatcatcher, as described by Dr. H. C.
Oberholser (1938), is "usually quick, but the bird does not
ordinarily travel far without stopping. Sometimes it flies rather
high, particularly when passing from one high tree to another, but
it is usually seen flitting about the underbrush." The
character of the flight is somewhat undulating or wavering rather
than direct, with rapid wing beats, and is similar to that of many
other very small birds; but the gnatcatcher can readily be
distinguished in flight by the length of its tail. Even at some
distance the observer has no difficulty in recognizing a
gnatcatcher in flight, while chickadees, kinglets, and small
warblers pass unnamed. P. A. Taverner and B. H. Swales (1908) gave
an idea of the capabilities of this species for performing
sustained flights when they listed it among the migrating birds on
the southward crossing from Point Pelee, Ontario. The gnatcatchers
they saw were unable to face the heavy wind prevailing at the time
of the observation, and had to come back ashore, tacking just as a
man would do in a boat, but the inference was that, under
favorable conditions, the crossing would be completed
successfully.
Certainly the most expressive feature of the gnatcatcher--as of
its larger counterpart, the mockingbird--is its long, ever-active
tail; now up and down, now from side to side, it is never for an
instant at rest. Under stress of great excitement, the bird seems
to try to combine these two motions at once, and achieves a
ludicrous impression of circular motion.
The gnatcatcher's manner of feeding is similar to that of many
other small birds, yet it differs in some respects from the
methods employed by its most frequent associates even though its
food, in winter at any rate, is probably the same as theirs. In
its gleaning of the twigs and leaves of trees and bushes it tends
to maintain an upright position and never (as I recall) hangs
beneath a twig, as is the chickadee's constant habit. Like the
kinglets, it often hovers before a leaf or terminal twig to secure
some morsel that cannot be reached from above, but it does not
indulge in this habit with the frequency of the kinglets. Unlike
the creepers and the nuthatches, it is seldom or never seen on the
trunks or large branches of trees. It is adept as a catcher of
flying insects (many other kinds besides gnats!) and even in
winter is often seen to secure food in this way. Its darts after
flying insects differ markedly from the long swings of the true
flycatchers, for its forays are seldom more than five or six feet
in extent and are usually vertically upward with a quick drop back
to the starting point. Again, unlike the flycatchers, it does not
perch motionless and wait for passing insects; and I suspect that
much of its catching of flying insects is by way of retrieving
prey that, disturbed by the bird's actions among the leaves, makes
a sudden flight to escape capture. Rarely, when the gnatcatcher is
feeding in low bushes, it drops momentarily to the ground to pick
up some object that attracts its attention; but it is no sense a
ground feeder for it does not search for food while it is on the
ground.
Field marks.--The blue-gray
gnatcatcher, one of our smallest birds, can be distinguished from
all other very small birds of eastern North America by its clear
blue-gray upper parts and unmarked white under parts entirely
lacking in yellow or yellowish tints, especially when the coloring
is noted in conjunction with the slender build, long tall and
white outer tail feathers. The bird is longer, and therefore
apparently larger, than the kinglets because of the length of its
tail. The brown creeper, another tiny bird with a long tail,
differs notably in color, shape, and habit. The parula warbler,
another bluish-gray bird, lacks the long tail and always shows
white wing patches and some yellowish in the plumage.
No less a writer than John Burroughs (1880), when describing
the gnatcatcher, made an unfortunately inept comparison that has
been copied down the years in the writings of many of his
followers. He wrote: "In form and manner it seems almost a
duplicate of the catbird, on a small scale. It mews like a young
kitten, erects its tail, flirts, droops its wings, goes through a
variety of motions when disturbed by your presence, and in many
ways recalls its dusky prototype." Such a comparison would
never have occurred to an observer who knew the mockingbird,
for the points of similarity (except for size) between the
gnatcatcher and the mockingbird are truly striking--form,
proportions (even to the long, expressive, white-edged tail),
color value though not color tone, many characteristic movements
and attitudes, in fact in almost every feature except the lack of
white in the wings of the gnatcatcher. I once knew a tyro
bird-watcher who, not aware that altricial species attain full
body size before leaving the nest, spoke seriously of the
gnatcatcher as a tiny mockingbird.
The distinguishing mark of the male gnatcatcher in breeding
plumage--the black forehead and line over the eye--is useful as a
field mark only at very short distances. Many times I have tried
to see it, even with binoculars and in good light, but the
activity of the little birds usually defeated my efforts. Only at
the nest, when an approach to within a few feet is possible, have
I been able to detect it with ease and certainty. It seems to be
not generally known that this distinguishing mark is not present
in winter specimens.
Voice.--Unlike the winter wren and
the ruby-crowned kinglet, whose bid for fame rests as much upon
the surprising volume of sound as upon the beauty of their songs,
the gnatcatcher does not take high rank as a singer. To an
observer like myself, whose auditory nerves (with advancing years)
no longer react to high-pitched sounds of small volume, the
gnatcatcher must actually be seen in the act of singing before the
attention can be focused sufficiently to catch the sound. Once
heard, the song is appreciated as a finished performance. C. J.
Maynard (1896) immortalized it in this beautiful passage:
I heard a low warbling which sounded like the distant song
of some bird I had never heard before. . . . And nothing could be
more appropriate to the delicate marking and size of the tiny
fairy-like bird than this silvery warble which filled the air with
sweet, continuous melody. I was completely surprised, for I never
imagined that any bird was capable of producing notes so soft and
so low, yet each one given with such distinctness that the ear
could catch every part of the wondrous and complicated song. I
watched him for some time, but he never ceased singing, save when
he sprung into the air to catch some insect.
Other observers and writers, however, do not seem impressed by
its beauty. F. H. Allen writes that the song of this species is
"scrappy, formless, leisurely, and faint, and is delivered
somewhat in the manner of a Vireo while the bird flits about among
the branches. [He] found the phrase pirrooeet occurring
frequently in it." A. A. Saunders regrets that he cannot
describe the song in detail, since his collection of sound records
"contains only a few fragments from a single bird. The song
is long continued, of greatly varied rapid notes and trills, on a
high pitch, and of a squeeky or nasal quality. It is more curious
than beautiful."
Wells W. Cooke (1914) cited a unique variation when "one
bird was heard to give a long, and beautiful and perfect
trill"; and A. L. Pickens, writing from Paducah, Ky., strikes
a new note when he describes "one fact about the blue-gray
gnatcatcher most observers appear to have missed. It has decided
powers of mimicry. One of its most amusing performances is the
apparent imitation, in its almost whispering tones, of a flock of
crows, or else blue jays." He says that the first name he
knew for this species was "Little Mockingbird."
The song period commences with the reanimation of the
gnatcatchers about mid-March and lasts only until eggs are laid
and incubation is started in mid-April. Birds heard singing later
than that in the far South may be only the late nesters or those
that have lost their first nests and are preparing to try again.
Like many other song birds, the gnatcatcber has a mild revival of
ardor in the fall, and I have a few times heard its song in
October. A. F. Skutch mentions having heard one "sing a sweet
little medley in an undertone" in January in Guatemala.
The call note of the gnatcatcher is far better known, because
it is more easily heard, than the song. I find it variously
described by many observers and writers, most of whom use
combinations of the syllable zee in attempting to "phonotype"
it. Others liken it to "the twang of a banjo string";
and "a nasal twee, suggestive of the catbird's mew
but thinner, shorter and fainter." Any or all of these may
serve as aids to identification for one who hears the sound for
the first time, but to my ear it possesses a quality that defies
description in stereotyped terms. It is more long-drawn than a
chirp; not as clear as (more husky or "fuzzy" than) a
whistle; definitely not a trill--and there I have compared it
negatively with the more usual small-bird sounds, and still I have
not described it. However, the sound is characteristic of this one
species and, once heard, is readily remembered and recognized.
L. A. Stimson, writing of the gnatcatcher in its winter
quarters in southern Florida, mentions another note, "a
shorter, more abrupt call with less of the zz
quality."
Enemies.--It is little short of
incredible that so tiny a bird as the gnatcatcher can and does
successfully fill the role of foster parent to the young of the
much larger cowbird (Molothrus ater), but there are many
instances of this on record. Dr. Herbert Friedmann (1929) recorded
the gnatcatcher as "a not uncommon victim [of the cowbird]
and in some places a fairly common one." It must indeed be
the smallest North American species thus victimized. An extreme
case is given by M. G. Vaiden, who, writing from the Yazoo
Mississippi Delta of Mississippi, states that he has
examined 12 nests of the gnatcatcher since 1919 and has found only
two of them without cowbirds' eggs. In one instance, on June 4,
1939, he found a nest that "contained four gnatcatcher eggs
and three cowbird's eggs," implying that other parasitized
nests examined by him had contained fewer than three. In another
nest he found "two young gnatcatchers and two young of the
cowbird." Of the two nests that had not contained cowbird's
eggs, only one was definitely immune, since the gnatcatcher was
incubating her own eggs when discovered. In the other, the
gnatcatcher had only commenced to lay, for the nest contained but
a single egg, and the observer concluded that the cowbird
"just had not located the nest yet," for he is "of
the opinion it later on did have cowbird eggs." Thus we have
a known 83 percent and a possible 92 percent parasitization, which
is, of course, too high for any species to survive if it applied
to more than restricted areas. Ben J. Blincoe (1923) watched a
pair of gnatcatchers attacking persistently a female cowbird and
driving it away.
The gnatcatcher probably suffers to some extent from predators
and nest marauders--undoubtedly a few are taken by sharp-shinned
hawks and screech owls, and perhaps some others succumb to attacks
by loggerhead and migrant shrikes--but there is nothing to
indicate that this species is singled out, nor, on the other hand,
would it be expected to enjoy greater immunity than other species
of comparable size within its range. However, a surprising
instance of seemingly selective predation--though this may be as
localized in its application as is the gnatcatcher-cowbird
relation just cited from Mississippi--was given by S. A. Grimes,
of Jacksonville, Fla., who wrote (1928):
Probably the greatest enemy of the Gnatcatcher is the
Florida Blue Jay [Cyanocitta cristata florincola]. I have
seen the Jay in the act of pilfering the smaller bird's nest
perhaps a score of times. One such episode remains singularly
vivid in my memory. . . . When the Jay alighted on the rim of the
nest, the Gnatcatchers were frantic and darted wildly at him,
though so far as I could see neither actually struck him.
Unperturbed, the Jay. . .grasped an egg in its beak and flew to a
limb some twenty feet from the nest. I watched three trips to the
nest, one egg being taken each time. I am inclined to believe that
the Jay did not take all the eggs, for usually the nest is pulled
apart after the last egg is eaten. And on the third visit the
robber appeared annoyed with the continued attacking of the owners
and flew with the egg to a tree some distance away before stopping
to eat it. He did not return to the nest. . . .
Fall.--In the northern part of its
breeding range the gnatcatcher is one of the first species to
withdraw from its summer home, and mid-August often sees the last
of them there. Farther south they linger much later, temporarily
joining the wandering groups of small woodland birds headed by the
chickadees and titmice.
In northern Florida and southern Georgia and Alabama, where the
gnatcatcher is resident, there is a gradual increase in numbers in
fall as birds from the northward pass through, then an equally
gradual subsidence until the small winter population becomes
stabilized. It is all so quietly and unobtrusively done that,
unless a constant observer actually records numbers of birds seen
on each trip afield, he is not likely to realize until late in the
season what has taken place before his eyes. October is the time
of greatest abundance, and by mid-November only a few gnatcatchers
remain.
In southern Florida, where the gnatcatcher is not normally
present in summer, its fall arrival is, of course, noticeable if
not conspicuous. L. A. Stimson writes from Miami: "In fall
its migration into this area is in an increasing crescendo over a
short period [leading up to its extreme abundance in winter]. Its
first appearance will be made by one or a very few individuals,
and a week later it will be common."
From the southern United States, the gnatcatcher's progress to
its tropical wintering grounds is presumably by way of the land
masses and not by direct flight across the Gulf of Mexico, for I
have never found a gnatcatcher among the many specimens of known
trans-Gulf migrant species killed by striking the lighthouse at
Pensacola, Fla., nor can I find a record of any having been killed
at any other of the Gulf coast lights.
Winter.--The blue-gray
gnatcatcher's winter home in the United States embraces the
coastal regions of South Carolina and Georgia, all of Florida, and
a strip of the Gulf coast from northern Florida to Texas. In the
northern part of this area it is uncommon to rare, but it becomes
common in extreme southern Louisiana and is abundant in southern
Florida and southern Texas.
Arthur T. Wayne (1910) wrote of it in the Charleston, S. C.,
region: "The birds are sometimes very hard to detect during
the winter, and at that season frequent the interior of large
swamps where they find food and shelter." Another southern
observer, S. A. Grimes, wrote (1928) from Jacksonville, Fla., that
it "is easily overlooked in winter, being rather retiring and
feeding mostly in the higher foliage." My experience with
wintering gnatcatchers in the similar--or even colder--climate of
extreme northwestern Florida and southern Alabama is widely at
variance with these last two observations. Here, although the
gnatcatcher is far from common, it is widely distributed, ranging
low as well as high in every well-wooded habitat except pure
stands of pine. Alone, and usually silent in winter, it could
easily be overlooked, but I have found it almost invariably
associated with Florida chickadees and tufted titmice--and what
could be easier to find than a titmouse! A typical
chickadee-titmouse winter group of small birds comprises half a
dozen each of titmice, chickadees, ruby-crowned kinglets, and
myrtle warbiers, a blue-headed vireo, an orange-crowned and a
yellow-throated warbler, and a gnatcatcher or two. The scolding
note of the titmouse is the signal for the observer to look sharp
for the rare winter visitors that, when present, attach themselves
to these wandering bands of small fry, so in the course of a
winter, I see many gnatcatchers.
The gnatcatcher is not susceptible to freezing temperatures and
has been known to withstand successfully such extreme as 16o
F., provided these frigid spells last only a day or two; but the
severe and protracted freeze of January 1940, when ice formed in
northern Florida every night for two weeks and on several days did
not thaw all day, caused the complete disappearance of the
gnatcatcher from the Pensacola region until the advent of spring
migrants. During the following winter of 1940 - 41, few were seen,
although migrants and nesting birds had seemed no less abundant
than usual in season. It was not until the second winter after the
"big freeze" that the gnatcatcher could again be
expected with confidence in every titmouse group.
Farther south in Florida the gnatcatcher reaches its peak of
winter abundance. L. A. Stimson, describing its occurrence in the
extreme southern end of the state, writes: "In the winter the
gnatcatcher seems to show no favoritism as to habitat. It may
readily be found in the city [of Miami] in fruit, native or exotic
trees; in the open country in typical hammock trees; in pine
woods; in the cypress; in the mangrove, buttonwood or bay fringes
of the coast or swamps; and along the Tamiami Trail it will be
found in the low willows where taller trees are absent. During its
stay here the gnatcatcher associates freely with other insect
eaters, wintering warblers, western palm, myrtle, yellow-throated,
prairie, parula, black and white, black-throated green; the
vireos, white-eyed and blue-headed; and the ruby-crowned kinglet.
Woodpeckers, wrens, yellowthroats, and cardinals will frequently
be found in the same clump of trees. In fact its call note is
often the guide to a good 'bird tree'."
Alexander Sprunt, Jr., writes from Okeechobee, Fla.:
"Gnatcatchers swarm on some days. The hammocks and canal
banks in perfectly open country have hundreds of them, and the
characteristic zee-e-e-e note sounds in one's hearing at
every stop. I have seen as many as six in one small willow. They
frequent the oak and cabbage palm hammocks and the willows,
myrtles and other growth typical of the banks of the drainage
canals. There might be a stretch of open prairie for miles about
such a place, but there they are! It is certainly one of the
typical passerine species of this area in mid-winter."
Beyond our limits, in Guatemala, Alexander F. Skutch considers
the gnatcatcher an abundant winter bird at middle altitudes--from
2,000 to 7,000 feet above sea level--and states that
"although the records of its occurrence range from the
lowlands to the summit of the Volcan de Agua (12,100 feet), it is
not often seen at either extreme; and it seems likely that the
birds taken at very high altitudes were migrating rather than
settled in their winter home. But I found it fairly common during
the winter months in the open woods of pine and oak in the lower
portions of the highlands among the orchards and thickets about
the shores of Lake Atitlan and among the shade trees of the great
coffee plantations on the Pacific slope down to about 2,000
feet." While he finds that "the gnatcatchers may at
times form small flocks of their own kind," the habits of
these tropical visitors seem to conform to the social pattern of
the birds that winter within our limits, for they "attach
themselves singly to flocks of warblers, the Tennessee warbler in
the coffee-growing districts, the Townsend warbler at higher
elevations." But he suspects that "when several of the
birds flock together, they are females or immature individuals,
for the adult males do not seem to get along together."
Length of sojourn is indicated by Skutch's "only record which
would indicate the date of arrival--one from Huehuetenango for
September 11, 1934," at which time he saw several
individuals. He also cites Griscom's "extreme dates for the
occurrence of the species in Guatemala as September 7 and March
3."
Blue-gray Gnatcatcher*
Polioptila caerulea
Contributed by Francis
Marion Weston
*Original Source: Bent,
Arthur Cleveland. 1949. Smithsonian Institution United
States National Museum Bulletin 196: 344-364. United States
Government Printing Office
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