Bent Life History of the Blue-gray Gnatcatcher

Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.

Bent Life History for the Blue-gray Gnatcatcher - the common name and sub-species reflect the nomenclature in use at the time the description was written.

 

BLUE-GRAY GNATCATCHER
POLIOPTILA CAERULEA CAERULEA (Linnaeus)

HABITS

CONTRIBUTED BY FRANCIS MARION WESTON


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 every-day 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 (MS.) 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 [sicl 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 silvifiora 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 virginicmna) "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 (MS.) mentions having seen a gnat catcher in northern Florida "picking the petals from dewberry blos soms [Rubus triviatis] 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 tine. 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 con crete 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 within 10 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 (Osmurtda einnamomea).

Measurements of two nests were kindly furnished by W. P. Proctor (MS.). One was: outside, 2 inches diameter by 2}~ deep; inside, iX inches diameter by lY~ deep. The other measured: outside, 2% inches diameter by 2% deep; inside, 1% inches diameter by 1% deep. The striking feature of both these sets of figures is the difference between the inner and outer depths: l% inches in the first nest and 74 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: i Y~ by 1 Y~ 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 (MS.) 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 (MS.) 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 (MS.) 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 bluegray 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 (MS.), 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 (MS.): "At some nests, both birds sit on the eggs; at others, t.he 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 tune 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. Sometunes larger prey is brought in, large enough, according to W. P. Proctor (MS.), 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. Grlines (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 (MS.) 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 tbat, 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 upperparts becomc 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 (MS.): "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 tines, in fact, except during the enforced inertia of incubation.

In defense of its nest, the gnatcatcher's small size places it at a dis.. advantage 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 (MS.) 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 h~fs no difficulty in recognizing a gnatcatcher in flight, while chickadees, kinglets, and small warbiers pass unnamed. P. A. Taverner and B. II. 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 upperparts and unmarked white underparts 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, that 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 plum~ age: 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 (MS.) that the song of this species is "scrappy, formless, leisurely, and faint, and is delivered somewhat m 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 (MS.) 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 trils, on a high pitch, and of a squecky 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 (MS.) from Paducali, 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 (MS.) 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 tïo identification for one who bears 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 (MS.) of the gna.tcatcher 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 (MS.), who, writing from the YazooMississippi Delta of N{ississippi, 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 cristeta florincota]. 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 Gnatcatehers 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 midAugust 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 thue 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 (MS.) 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 fe v 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 north western 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 16~ 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 (MS.), 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 (MS.) from Okeechobee, Fla.: "Onateatchers 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 (MS.) 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 Volc~n 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 Atitltin 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."

DISTRIBUTION
Range: Southern Canada to Guatemala.

Breeding range: Toward the limits of its range the blue-gray gnatcatcher is rather sporadic in its occurrence, nesting one year and perhaps not appearing again for several years. It has been found breeding north to northern California (Covelo, Baird, and probably Yreka); central Nevada (Kingston Creek and Nyala); northern Utah (Boulton, Stansbury Island, and the Uinta Valley near Vernal); southwestern Wyoming (Green River; it has occurred at Torrington in the eastern part of the State); southern Colorado (Cortez and Pueblo; occurrences have been recorded at Two Bar Spring, Moffat County, Grand Junction, and Boulder); western and central Oklahoma (near Kenton, Oklahoma City, and Ponca); eastern Kansas (Wichita, Manhattan, and Blue Rapids); southeastern Nebraska (Lincoln and Omaha); northern Iowa (Hawarden, one record, Grinnell, and National); southeastern Minnesota (Minneapolis, Marine, and Frontenac); southern Wisconsin (Madison and Milwaukee; occasionally north to New London); southern Michigan (Grand Rapids, Lansing, Ann Arbor, and Plymouth); extreme southern Ontario (Mitchells Bay, Plover Mills, and 1-lamilton); western New York (Geneva); southwestern Pennsylvania (Beaver and Harmarville); and northern New Jersey (Somerset and Essex Counties). East to eastern New Jersey (Essex County, Sea Isle City and Cape May); and the Atlantic Coast States to central Florida (New Smyrna and Deer Park); and the Bahama Islands (Abaco and New Providence). South to the Bahama Islands (New Providence); central Florida (Deer Park and Braden River); Cozuinel Island, Mexico, and YucatAn (Chichen ItzA); Tabasco (BalancAn) ; Chiapas (Palenque) ; Oaxaca (Oaxaca); and Lower California (Cape San Lucas). West to Lower California (Cape San Lucas, Comondu, and the Sierra San Pedro MArtir); and western California inside the Coast Range (San Diego, Pasadena, Stockton, Napa, and Covelo).

In addition there are many records of individuals north of any known breeding localities. Many of these are late in summer or in fall and suggest the possibility that some may ho individuals that have wandered north after the breeding season; some are probably migrating from nesting sites that man has not found. These records extend north to Sault Ste. Marie; Mackinac Island and Douglas Lake, Michigan; Goderich aad Toronto, Ontario; Montreal and Quebec, Quebec; and the coast of New England as far north as Portland, Maine.

Winter range: The blue-gray gnatcatcher is found in winter north to central California (Muir Beach, Mann County; Kettleinan Hills, Deat.h Valley, and Needles); two specimens taken at Ashland, Oreg., February 4, 1881, are in the British Museum; southern Arizona (Papago Indian Reservation, Tucson, and the Rincon Mountains); Sonora (Punta Penascosa and Tesia); Sinaloa (Caliacan); Jalisco (Ocotlan); Nuevo Le6n (Monterey and Rodriguez); Tamaulipas (Nuevo Laredo and Camargo); southern Texas (Brownsville and rarely San Antonio); southern Louisiana (Chenier au Tigre, Lecompte, and New Orleans); Mississippi (Bay St. Louis and Biloxi); northern Florida (Pensacola and Tallahassee); eastern Georgia (Fitzgerald and Blackbeard Island; occasionally Milledgeville and Augusta); and the coastal region of South Carolina (Charleston). It has been recorded in midwinter at Collington Island, N. C., and Washington, D. C. East to South Carolina (Charleston), the Bahama Islands (Abaco, Caicos, and Great Inagua). South to the Bahamas (Great Inagua); Cuba (GuantAnamo and Isle of Pines); and Guatemala (Los Amates and Alotenango). West to Guatemala (Alotenango, Sacapulas, and Chanquejelve); Gaxaca (JuchitAn); Guerrero (Chilpancingo); Lower California (Cape San Lucas, Cedros Island, and San Telmo); and California (Santa Catalina and Santa Cruz Islands, Santa Barbara, and Muir Beach).

The species as outlined has been divided into several subspecies or geographic races. The eastern blue-gray gnatcatcher (P. c. eaerulea) breeds from Nebraska, Kansas, Oklahoma, and Texas eastward; the western gnatcatcher (P. c. amoenissima) breeds from California to Colorado and south to northern Lower California and Sonora; the San Lucas gnatcatcher (P. c. obseura) breeds in the southern half of Lower California.

Migration: Late dates of spring departure are: Cuba : Habana, May 13. Texas: Somerset, May 5.

Some early dates of spring arrival are: North Carolina : Raleigh, March 16. Virginia: Lawrenceville, March 21. West Virginia: Bluefield, March 28. District of Columbia: Washington, March 6. Pennsylvania: Waynesburg, April 6. New York: Brooklyn, April 8. Arkansas: Monticello, March 16. Tennessee: Nashville, March 12. Kentucky : Madisonville, March 27. Indiana: Bloomington, March 22. Ohio : Cincinnati; March 29. Michigan : Ann Arbor, Apr11 11. Missouri: St. Louis, xiarch 31. lowa: Keokuk, April 12. Wisconsin: Beloit, April 23. Nlinnesota: NIinneapolis, April 18. Oklahoma: Copan, March 20. Kansas: Independence, March 31. Nebraska: Fairbury, April 6.

Some late dates of fall departure are: Minnesota: Minneapolis, September 7. Wisconsin: Madison, September 11. Iowa: Hillsboro, September 15. Missouri: Columbia, September 18. Michigan: Grand Rapids, October 5. Illinois: Rantoul, October 15. Ohio: Toledo, October 5. Kentucky: Eubank, September 24. Tennessee: Athens, October 6. Arkansas: Helena, October 28. New York: New York, September 10. Pennsylvania : MeKeesport, September 29. District of Columbia: Washington, September 13. West Virginia: Bluefield, September 5. Virginia : Naruna, September 22. North Carolina: Chapel Hill, October 4. South Carolina: Spartanburg, October 10. Georgia: Athens, October 17. Alabama: Leighton, September 5.

Some early dates of fall arrival in the winter home are: Cuba: Habana, August 13. Guatemala: Remote, Pet~n, July 30, Panajachel, September 7.

Egg dates: Lower California: 12 records, May 8 to July 23; 7 records, June 25 to July 19.

California: 108 records, April 5 to July 12; 58 records, May 16 to June 12, indicating the height of the season.

South Carolina: 11 records, April 19 to May 22; 7 records, May 7 to May 22. Texas: 11 records, April 15 to May 25; 6 records, April 23 and April 24.



WESTERN GNATCATCHER
POLIOPTlLA CAERULEA AMOENISSIMA Grinnell
HABITS

Under the name western gnatcatcher (Polioptila caerulea obscura) Mr. Ridgway (1904) described the blue-gray gnatcatchers of the Southwestern United States, from the interior of northern California to northern Mexico and Lower California, as far south as Cape San Lucas, as "similar to P. c. caerulea, but gray of upper parts slightly duller and black at base of inner web of outermost rectrix more extended, usually showing beyond tip of under tail-coverts." His type came from San Jos6 del Cabo, and he evidently thought it might be only a winter visitor, for he said of its occurrence there "in winter only?". He therefore applied the name obscura to all the western gnatcatchers.

Subsequently, Dr. Joseph Grinnell (1926) discovered that "the materials now accessible in sufficient amount show that there is a separately recognizable race of Blue-gray Gnatcatcher resident in the restricted faunal area known as the Cape San Lucas district of Lower California." He therefore restricted the name obscura to the Lower California race and proposed tbe name amoenissima for the birds of the west outside of the southern tip of Lower California. He characterized amoeni.ssima as "similar to P. c. obseura Ridgway, of the Cape San Lucas region, but wing and tail (especially the tail) longer, bill slightly slenderer, and median lower surface less clearly white, more imbued with very pale gray.~~ The 1931 Check-list gives the breeding range of this form as "from northern interior California (Shasta County), southern Nevada, southern Utah, and Colorado (El Paso County) south to northern Lower California, Chihuahua, Sonora, and Colima."

In California the favorite haunts of the western gnatcatcber are the warm, dry foothills covered with chaparral, small oaks, and other small trees and underbrush, as well as the groves of cottonwoods in the river valleys. In the Lassen Peak region, according to Grinnell, Dixon, and Linsdale (1930), "willow, valley oak, mauzanita, digger pine, blue oak, and buckbrush are all plants in which individul gnatcatchers were seen. However, the portion of the section most favorable for this bird, as indicated by concentration of breeding birds to cover practically the whole of such area, was the tract of blueoak-covered bills north of Red Bluff and west of the Sacramento River. There the park-like arrangement of the trees, each with many slender branches covered with copious foliage, and with the intervening spaces between the trees of a uniformly short distance, seemed ideally to fulfill the requirements of this bird for nesting and foraging activities."

In Arizona we found this gnatcatcher only fairly common in the foothills of the Huachuca and Dragoon Mountains and in the wider, lower portions of some of the larger canyons, mainly between 5,000 and 6,000 feet, but never out on the lower plains or at higher elevations in the mountains among the coniferous forests. Some of the foothills where we found the gnatcatchers were dotted with small black-jack oaks, with more or less even, open spaces between them, covered with mountain-misery and various other shrubs. A typical canyon haunt was in Miller Canyon in the Huachucas. This was heavily wooded along the stream with a row of big sycamores, ashes, walnuts, maples, and cedars; at its wide mouth was an open, parklike forest of large black-jack oaks in which numerous Arizona jays were nesting; farther up the canyon were smaller oaks of various kinds, madrones, manzanitas, and thickets of various kinds of shrubs. The gnatcatchers seemed to prefer the smaller oaks.

Territory: In densely populated areas western gnatcatchers seem to establish and maintain fairly definite breeding territories. Grinnell and Storer (1924) write:

During the early spring immediately after their arrival from the south, the gnatcatchers are to be seen in pairs, the male in close attendance upon the female. When the latter engages in the work of nest construction her mate remains in the vicinity, part of the time accompanying her on trips for building material or on foraging sorties. Otherwise he guards the nesting precincts against invasion of any rival male. All the while, in the heat of mid-afternoon as well as at other hours of the day, the male gnatcatcber utters his fine wheezy song at frequent intervals, and the female answers from time to time in similar tone of voice with single notes.

When settled for nesting each pair of gnatcatchers is strongly localized. Each keeps within a radius of not more than a hundred yards from the nest tree. This localization permits an observer to take a more accurate census of nesting pairs than is possible with many other birds. At Black's Creek, near Coulterville, our own counts led to an estimate of 64 breeding pairs of the Western Gnatcatcher to each square mile in that immedate district. Carrying these figures further, in consideration of the estimated area of the Upper Sonoran Zone included in our Yosemite section, we find a total gnatcatcher population just before the appearance of the new broods, to consist of 50,000 individuals.

Nesting: The same observers say that "the nests are of deep cupshape, and are constructed throughout of light-weight materials. A framework of fine grass stems forms the main wall, and this is covered both inside and out with softer substances. The outside is felted with lichens such as abound on the bark of blue oaks, with a few grass seed hulls, some small oak leaves, and occasionally a feather or two, the whole being held together with spider web. The inside of the nest is lined almost entirely with feathers, laid flatways of the inner surface. Whatever the purpose of the bird in constructing such a nest, the form and outside appearance are usually such that the structure might easily be mistaken for a weathered stub or a small accumulation of d6bris."

They mention a typical nest in a blue oak as "situated about 10 feet above the ground near the periphery of the tree, amid small twigs and branclilets, and rested directly on a horizontal branch." Others were found "in crotches of small blue oaks, and several were found in greasewood (chamisal) bushes, at a height of not more than 3 feet from the ground."

It seems to be a characteristic habit of the western gnatcatcher to change the location of its nest once or twice before being sufficiently satisfied with the site to finish the structure. Several observers have reported that nesting material has been entirely removed from an unfinished nest and used to build a nest in another location. This may be because the birds saw that their nest had been discovered and was unsafe for eggs or young; some birds are very sensitive to human intrusion. Corydon Chamberlin (1901) says: "Of the first few nests I saw being built none were finally occupied on their original site. One pair near my camping place moved their nest and made it over three times before being satisfied to deposit eggs in it. Each time that the nest was nearly complete, the birds would discover a more suitable site and then the work of tearing down would begin and it would be moved piece-meal to the new place and until scarcely a vestige of the nest remained in the old location. The third and final resting place for this nest was in the main crotch of a small white oak bush at such a height that I could just reach the nest by standing on tip toe."

He mentions several other nests, found in Tuolumne County, Calif., one of which was "in the main crotch of an alder tree 30 feet from the ground, the tree being in a creek bed." Another, 6 feet from the ground on a small horizontal oak limb, "was made in between the stub of a small twig and a live twig carrying a bunch of leaves that hung over the nest like a parasol.

"Perhaps the most unique nesting site ever seen of this species was the top of a pine cone in a sprawling bull pine. The cone was on a lonely limb fully thirty feet above the ground at the butt of the tree, but as the tree hung over a gully the nest was double that distance vertically from the ground."

Most nests of the western gnatcatcher are more or less decorated with lichens of colors to match their surroundings, though generally not as thickly covered as the nests of the eastern race. But Mr. Chamberlin mentions two nests that were entirely deVoid of lichens; these were in oaks that had been killed by fire, as the whole area had been burned over; as there were no lichens available, the nests were decorated with bits of burnt bark, which helped to make them match their surroundings in the charred trees.

Harriet W. Myers (1907) found a nest "near the top of a holly bush that had grown so tall that it was more like a tree than a shrub" and another"on the south side of a tall, straight eucalyptus tree about twenty feet from the ground, its only supports being the tiny twigs that grew out from the side of the tree."

California nests of western gnatcatchers have been recorded at heights as low as 3 feet in bushes and as high as 45 feet in oaks.

The only nest we found in Arizona was 7 feet from the ground on a horizontal limb of a black-jack oak (p1. 44), in Miller Canyon, in the Iluachuca Mountains.

Eggs: The four or five eggs that make up the usual set for the western gnatcatcher are indistinguishable from those of the eastern subspecies. The measurements of 40 eggs average 14.3 by 11.4 millimeters; the eggs showing the four extremes measure 16.2 by 11.5, 14.0 by 12.0, 13.5 by 11.5, and 13.7 by 10.7 millimeters.

Young: The incubation, brooding, and care of the young seem to be performed by this western subspecies in the same manner as by the eastern blue-gray gnatcatcher. Mrs. Myers (1907) gives the following feeding record for one brood:

On this same morning from 7:25 to 8:25, the birds fed thirty-five times, less than two minutes apart; the male twenty-seven times, the female fourteen. The next morning, in the hour from 6:37 to 7:37, the birds fed forty-six times, the male thirty-six and the female twenty-four times. In looking over my notes I find that the birds fed more often early in the morning than later in the day.

In five hours, 6:30 to 11:30, they fed one hundred and fifty-two times, or an average of thirty-eight times an hour. Allowing sixteen hours to their day, we can estimate that they fed six hundred and eight times. The word "gnatcatcher" proved to he a misnomer, the food brought so often being small white worms.

Food: The food of the western gnatcatcher is not essentially different from that of its eastern relative. Professor Beal (1907) makes the following general statement on the food of the California gnatcatchers: "No complaints have been made that these busy creatures ever injure fruit or other crops. Their food is composed almost exclusively of insects, which they hunt with un tiring energy from morning till night. Like the titmice and kinglets, gnatcatchers are fitted by nature to perform a service which larger species are unable to accomplish. There are hosts of minute insects, individually insignificant but collectively a pest, that are too small to he attacked by ordinary birds and are to be combated by man, if at all, only at great expense. It is to so deal with such pests that they may not unduly increase that these tiny birds would seem to be especially designed."

The behavior, voice, and general habits are similar to those of the eastern bird. It can be distinguished from the other California gnatcatchers by having the outer tail feathers white for their entire length; there is much less white in the tail of the plumb eous gnatcatcher, and hardly any in the tail of the black-tailed; the gray of the upperparts is lighter in the western than in either of the others. California jays have been known to destroy the nests of this gnatcatcher as well as to rob them of eggs or young; and Mrs. Myers (1907) has seen the little birds drive away a California shrike.

Dr. Friedmann (1929) says that the western gnatcatcher is victimized by the two western races of the cowbird, artemisiae and obscurus, in much the same way as the blue-gray gnatcatcher is imposed upon by the eastern cowbird.



SAN LUCAS GNATCATCHER
POLIOPTILA CAERULEA OBSCURA Ridgway
HABITS

As explained under the previous subspecies, this race of the bluegray gnatcatcher has been separated from the other western race on the slight characters there mentioned. It is found only in southern Lower California, from Cape San Lucas north to about latitude 280, where it is apparently resident. It probably does not differ materially in any of its habits from the more northern form. William Brewster (1902) says of it:

The Western Gnatcatcher is a rather common resident of the Cape Region, where it appears to be indifferent to conditions of mean temperatures or environment, for it occurs nearly everywhere from the seacoast (La Paz and San Jos4 del Caho) to the summits of the highest mountains (Sierra de la Laguna). Mr. Frazar found it breeding at San J05~ del Rancho in July. His first nest, discovered on the 7th, contained four eggs on the point of hatching, and was not disturbed. Two others, taken respectively on the 14th and 19th of the month, had full Bets of four eggs each, all freshly laid. One of these nests, built in the fork of a bush at a height of about five feet, measures as follows: Greatest external diameter, 2.25; greatest external depth, 2.00; internal diameter at top, 1.30; internal depth, 1.10; greatest thickness of walls, .50. The exterior is composed of gray, hemp-like, vegetable fiber and narrow strips of reddish brown bark, and is decorated with a very few lichens, all these materials being over-wrapped and kept in place by a nearly invisible tissue of spider-web. The interior is lined with fragments of silky cocoons and a few feathers. The other nest, which was placed in the fork of a small tree abouc ten feet above the ground, and which is essentially similar to the specimen just described, save that it has no lichens whatever, measures externally 2.15 in diameter by 2.10 in depth; internally, 1.40 in diameter by 1.50 in depth. Both nests are smaller and more compact than any nests of P. caerulea in my collection.

There is a set of eggs in the Doe collection, taken by J. Stuart Rowley at Mirafiores on May 8,1933; the nest was saddled on a branch of a palo blanco tree, 20 feet above ground. A nest in the Thayer collection, taken by W. W. Brown near La Paz on June 25, 1908, was placed between two upright stems of a bush, about 5 feet from the ground. The construction of this nest is similar to that of the nest described above; there are no lichens on it, but it has a decidedly gray appearance.

The eggs of the San Lucas gnatcatcher are similar to those of the species elsewhere. The measurements of 32 eggs average 14.5 by 11.2 millimeters; the eggs showing the four extremes measure 15.6 by 11.8, 14.3 by 11.9, 12.9 by 11.2, and 13.6 by 10.6 millimeters.