Horned Lark | Life Histories of North American Birds | A.C. Bent
Feather Pic Arthur Cleveland Bent

Life Histories of Familiar North American Birds
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Horned Lark
Eremophila alpestris [Prairie Horned Lark]

Contributed by Gayle Pickwell
[Published in 1942: Smithsonian Institution United States National Museum Bulletin 179: 342-356]

Out at the bleak end of the ecological series of bird habitats, which begins with the heavy forests and ends with the barrens, lives America's only true lark. *** Far from the treeless Arctics, far from the deserts, this lark finds as its barrens the plowed fields of the Midwest, the tree-denuded, wind-swept hilltops of the northeastern states, and those peculiarly unnatural artificial barrens, the hazards of these modern-day golf courses.

If for no other reason than that here is a bird nesting where no bird has a right to nest, a bird in a niche that demands not vegetation but lack of it, a bird alone and unique in its nesting site without a competitor and far out at the end of the series--if for no other reason than this purely ecological one--the prairie horned lark invites close study. But if we add to this the fact that it is a lark, a representative of our only lark, with the song of a lark, the ways of a lark, and many a habit and idiosyncrasy peculiarly its own, and that it is an intriguing bird of the open field, then the bird becomes even more interesting.

The prairie horned lark, because of its tendency to occupy the most barren regions as its home, interested me very early, for desultory observations of this bird were begun while still a boy in eastern Nebraska. The lark nests were found on the ridges of listed corn and an observation of a song still remains clear and trenchant. We were shocking wheat, hence it was mid-July, when a lark was seen climbing the air for his song. We watched him against the vivid sky during his long minutes aloft; were amazed by that final headlong drop to earth.

Study of the prairie horned lark was initiated in eastern Nebraska, continued intensively in northern Illinois (Evanston) for two years, then transferred to Ithaca, N.Y., and concluded. ***

Courtship.--Prior to the establishment of well-defined territories, fighting between males is promiscuous; after that fighting takes place only on territory boundaries, where two lark areas juxtapose. The males, at the boundary line, frequently strut before each other and often peck the ground furiously, like barnyard cocks, but all fighting is in the air. On a boundary this fighting often results in a curious game of "tit for tat," as the male larks chase one another back and forth. Every adventitious lark, wandering into established territories, is promptly evicted by the male. Such a bird will leave without protest. So far as noted, the female is never the direct cause of fighting; in fact fighting is most frequently noted when the female is brooding and the male is no longer attending her. Only once was a female noted driving out another lark, a male. She was defending a recent nestling.

The female has no courting maneuvers and was never observed to sing. Only once was she seen to importune sexual attention and then by a crouch and flutter similar to the actions of the English sparrow. The male struts frequently before the female with wings dropped, tail spread, and horns up. He will assume this attitude before another male at the territory boundary.

Nesting.--The literature shows a surprisingly large range of habitats in which the prairie horned lark has been known to nest. These habitats, resulting for the most part from agricultural activity or other human agencies, are those that most nearly result in barren conditions. It does not matter that these barrens may be seasonal or otherwise very temporary, if they are suitable for the initiation of nesting. That bare ground is the determinant is shown by the fact that variations of moisture, soil, elevations, and temperature will all be tolerated in the selection of nest sites. ***

Some typical Chicago marsh in the Evanston region was drained for a golf course. The course was later cut up into real-estate subdivisions; sewers were laid exposing a wide area of bare soil in the streetways; and old sand hazards remained here and there. This series of activities provided nesting sites for many larks. More than a score of nests were located in this area (about 90 acres) in 1926. A plot of vegetable gardens bordering this region on the west, where larks had probably nested for some years, was also subdivided and the vegetation subsequently neglected. Here several larks also nested.

The advent of vegetation in both areas and the demand of the lark for bare ground forced a seasonal succession of horned-lark breeding sites first from lot surface, to streetway, to sand hazard, to vegetable garden, in order that each was successively occupied by verdure.

In Ithaca, N.Y., one nest was located on the overturned sod of a former hay meadow. Most of the observations there made, however, were on a tract of ground that was largely fall wheat, partly fall rye, and the remainder devoted to experimental vegetable gardens. The growth of the wheat forced the larks from its surface by late May. The gardens and portions of the fall rye area that were turned under as green manure remained suitable throughout. Clean vegetable gardens will always present a considerable amount of bare soil, and the prairie horned lark is usually able to occupy such gardens until late in June.

A breeding territory was delimited by a male lark on February 7, 1926, at Evanston, Ill. From his selected territory he could not be driven. This territory was about 100 yards square. Late March snows disrupted all territories, and it was not learned whether the original sites were ultimately resumed or whether the same territory was maintained through more than one nesting. The pressure of vegetation in late May and June greatly modified the territories at Evanston and caused, eventually, the abandonment of most of those on the erstwhile golf course.

At Ithaca, N.Y., a male lark was forced to mark territory for the first time on March 13, 1927, though it had undoubtedly been established some time before this. Territories voluntarily marked were somewhat larger than those indicated when the birds were forcibly driven about. The regions of a breeding territory most frequently occupied were those boundaries that joined the territories of a neighboring lark.

The territories at Ithaca were much larger than those at Evanston, possibly because fewer larks attempted to occupy them. At Evanston they were seldom over 100 yards square, whereas at Ithaca they ran out to lengths of 300 yards and widths of 200 yards, in March and April. In general all suitable territory was occupied at Ithaca and most boundaries were established by the margins of unsuitable areas, though a large amount of suitable territory, extending beyond, was used only in part by the bird. Boundaries between males were often definitely established on ground that had no natural marker whatsoever.

The territory history of three pairs of larks was followed from March to June at Ithaca. One influence only modified the territories, namely the growth of vegetation. One territory, completely on fall wheat, was abandoned by the close of the second nesting in May. Another territory, in part on fall wheat and in part on the gardens, was gradually reduced to the gardens, from an area once 300 by 200 yards to an ultimate area about 100 yards by 50 yards. A third territory, almost entirely on the gardens, suffered no major reduction. But the owner of this third territory, which abutted that of the second, gave no ground to the latter.

Though most of the feeding was done on the nesting territories, a neutral feeding territory was discovered, and others were indicated because, now and then, the larks would go off on purposeful flights entirely out of their areas.

The female would mark the same territory as that marked by the male, and if anything she was more closely restricted to it than the male. She selected the nest site with little or no regard to the center of the area.

The literature contains four February records of nests and many records of March nests in many states, and two or three records of nests in July. I have records of nests from about March 21 to July 12, in 1926, at Evanston, Ill.; from about March 11 to June 28, in 1927, at Ithaca, N.Y.

It is suggested that such a strange phenomenon as that of a passerine bird nesting in March in eastern United States cannot be easily explained. The bird has too long a nesting season to explain it on conditions that might exist in early spring alone; and then, in the range where the prairie horned lark was studied, nests are frequently destroyed by inclement weather and many young die of starvation at this season. Since this bird demands barren conditions, and not verdure, for a nest site, the conditions are suitable very early, and it is suggested that an early-nesting physiological cycle may have been acquired in a more propitious climate and subsequently carried north and east. It is further noted that O. a. actia of California nests in March where conditions are quite ideal.

With one exception all of the 14 observed nests of March and April were not begun until the mean temperature rose above 40o F. for two or more days in succession. The exception was the initiation of a nest on the first day that the temperature rose above a mean of 40o F. Once weather conditions suitable for the initiation of nesting activities prevailed, no subsequent weather, no matter how severe, except deep snow only, would inhibit these activities. Even birds that had nested in March and whose nests were destroyed by late March and early April snows, would not renest until weather conditions were as given, though this necessitated a delay of nearly three weeks in two cases in Ithaca, N.Y. That this was a delay caused by weather is easily demonstrated by the fact that an exceptional case, as noted above, began renesting on a single suitable day, but two other larks waited two weeks longer for renesting or until weather again was suitable and for a longer period. It is known that two of these birds, and probably all, had former nests. ***

It is suggested that the discovery of nests during nest building is possible by locating first the calling or singing male. At this period the male will be attending the female closely and she will be discovered shortly. The status of nesting can always be determined by the actions of the female. During nest building she is very restless, runs here and there, flies up and away, but shortly returns. Eventually she may disclose the site of the nest excavation. These reactions are instinctive responses to the desire for nest concealment. All nest building seems to be done by the female.

During egg laying the discovery of a nest is at best accidental. Neither male nor female has been noted to approach a nest during this period. They express no solicitude beyond that of nest concealment, thus displaying a remarkable nonchalance, especially on the part of the female. This reaction is so marked that an observer can nearly always be assured of the status of nesting whenever it is noted.

When incubation has begun the behavior is very different, as is also the behavior after the eggs have hatched. These reactions will be noted later. During these periods nests may be located by a systematic search that involves driving the male about until the female is noted. She will flush from the nest and the male will go to her. Then a patient watch of the female will, after a variable length of time, disclose the nest. When young are being fed the male will, at times, disclose the nest much more quickly than the female, for he assists in feeding and has nest-concealing instincts that are very poorly developed. Though the nest of the prairie horned lark is never concealed from above, it fits its semibarren environment so closely that a promiscuous search over a breeding territory is nearly always tiresome and unavailing. An incubating or brooding lark, as will be discussed later, often remains close to her nest on a chilly day or very early in the morning or toward evening. Nests can be found under these circumstances by a systematic search of likely habitats and so flushing the bird from the nest.

No evidence of the use of a natural depression was noted either at Evanston or at Ithaca; all were dug by the female. According to Sutton (1927) and my own observations of O. a. strigata in western Oregon, this excavation is dug with both beak and feet. The nest is constructed usually at the edge or partially under a grass tuft or clod, which, in the case of the prairie horned lark, lies most frequently on the west, northwest, or north, possibly because the cold and violent winds of the early nesting season come from this direction. The body of the nest consists of coarse stems and leaves with a finer lining within. The time spent in nest construction varies from two to four days.

The majority of the nests of the prairie horned lark showed a variable amount of clods, pebbles, or similar items laid about the margin usually on the side away from the protective tuft or clod. These so-called "pavings" were always composed of the material most easily obtained regardless of its permanency. It is suggested that the purpose of "pavings," if there is a purpose, arises from the method of nest construction and from the desire of the larks to have a bare-ground nest approach.

Eggs.--The egg has a background of gray with an occasional greenish tinge, which, background is almost completely concealed with a fine speckling of cinnamon-brown. The cinnamon-brown often forms a denser ring about the larger end. The average size was found to be 2.25 cm. by 1.55 cm. The eggs of natural second sets seemed to be a trifle larger than the first sets of the same individual. The number of eggs per set varied from two to five; the average was about four, the sets of fewer numbers occurred early, those of larger number, later. [AUTHOR'S NOTE: The measurements of 50 eggs average 21.6 by 15.7 millimeters; the eggs showing the four extremes measure 24.6 by 15.5, 23.1 by 17.3, 18.3 by 15.0, and 21.6 by 14.5 millimeters.]

Incubation.--The incubation period was determined to be 11 days. Only the female incubates.

The male shows little or no solicitude during the incubation period. The female has a highly developed series of automatic instincts of solicitude, which are modified by time of day, condition of weather, and frequency of disturbance. The most highly developed and probably the most recently acquired of these has been given the name nest concealment by abandonment, or casual abandonment. The female leaves the nest, in this reaction, when an intruder is at a long distance, and flies quietly away, low against the ground, and does not show other solicitude for a very considerable period. The distances of the intruder from the nest during this reaction vary from 25 to 100 yards or often farther, a greater distance, it will be noted, than would disturb even a timid lark under other circumstances. A reaction that in many ways is the reverse of this, but still a marked exhibit of solicitude, is that called distress simulation. This consists of a precipitate flushing and rapid flutter over the ground after the nest has been approached closely. This reaction would be given most frequently on very cold days, in the dusk of very early morning or evening, and when the bird was flushed very shortly after she had returned to the nest. It is certainly more primitive than the first reaction here described and is probably a culmination of the more frequent distraction display that most birds present when their nests are disturbed. Between concealment by abandonment and distress simulation there occurs a complete gradation, which, since the reactions are exact opposites in expression, involves a curve that drops from the first to the zero point and then rapidly ascends to the expression of the latter. Thus, between the two, lessened expressions of either reaction would result, with a serious hiatus midway in which the incubating bird would allow an intruder to approach closely and then leave without an expression of either type of solicitude. Experimental flushing of an incubating bird from a blind showed that the bird, in one case, would give distress simulation if flushed in an interval that was less than two minutes from the time of her return; but would give casual abandonment if flushed after an interval of five minutes. A female lark, shortly after being forced from a nest, would express her agitation by aimless ground pecking, and, to be sure, would eventually be driven by the incubation urge to return to the nest even though an intruder might be much nearer than he had been when the nest was originally abandoned. This complex of instincts involved both the urge to incubate and the urge to protect. The instinct to protect, by whatever method, would all be overshadowed in time by the instinct to incubate.

Young.--With the exception of those nests of early April, in which incubation began before the set was complete, all young hatched within an hour or two of each other. The young are fed within an hour or two following hatching. In most cases the male assisted the female in feeding the young. In carefully observed cases he visited the nest less often but brought greater burdens and fed more young at a visit than did the female. A total number of observed feedings during one day (April 30, 1926) was 108. The male fed 39 times and the female fed 69 times.

Observations of the adults and dissection of a few nestlings showed that some vegetable matter (weed seeds) is fed early in spring but that even in March most of the food is animal matter. Later in the season grasshoppers become conspicuous in the diet. The adults dig up both cutworms and earthworms.

The male shows solicitude for the nest and its contents for the first time after the hatching of the eggs. His solicitude is restricted to calls. The female will leave her brooding in typical concealment by abandonment when conditions are appropriate as when incubating; likewise she will go from the young in distress simulation under conditions as noted previously. Proportionately the number of concealments by abandonment decreases and distress simulations increase slightly with young in the nest. Other reactions, which are various primitive expressions of solicitude, or intermediates of the two just mentioned, increase proportionately. Perhaps a return of more primitive instincts indicates a sum total of greater solicitude. Since the female is frequently absent from the nest in food foraging, she will come in, as an intruder approaches, with calls and cries. One or two references in the literature show that the reactions to dogs is the same as to man, but that hens are driven off by entirely different methods.

The larks removed all excreta throughout the full extent of nest occupancy. Early in the season much of the excreta was eaten by the adults; later it was dropped to the ground 50 or more feet away. This seasonal change of habit may have been related to the available food supply. The instinct compelling excreta removal proved itself very powerful, at times overcoming strong solicitude for nestlings and even fear.

The young showed a psychic development closely related to their rate of growth and not to their age. Young of the same age or but one day younger than their nest mates often presented a psychic development two to four days behind them. This was due to uneven feeding, which occurred frequently early in spring because of uneven hatching or an inadequate food supply.

Normal nestlings give a food response indiscriminately up to the fifth or sixth day. Just prior to this time their eyes open. Following this they respond not at all or momentarily only. They withdraw at a touch from the hand on the sixth day and sink back quietly into the nest in crouch-concealment between the seventh and ninth days. Upon being removed from the nest at this age they sit quietly upon any object upon which they are placed; prior to this time they wriggle about when taken from the nest. They leave the nest on the tenth day and then express fear by hopping and calling wildly when disturbed. An expression of this type of fear, prior to the tenth day, would take them from the nest prematurely.

Weight-growth curves show a gradual increase over the first three days, a very precipitate rise (except for April nestlings) for the next three or four days, a marked leveling during the seventh and eighth (in one case the sixth), and a gradual rise during the ninth and tenth. Nestlings in May grew slightly more in the same period than a nestling in June and much more than a nestling in April. This discrepancy of growth seems closely (though perhaps indirectly) correlated with the temperatures of these seasons.

A lessening in weight growth occurs, normally, between the seventh and eighth days. This is brought about by the simultaneous unsheathing and drying of most of the feathers. On the other hand, growth in length shows, if anything, an acceleration at this period due to the extension of the tail. Marked variations in growth occurred in the various broods measured and in the different young of the same brood. This was brought about by two things: the fact that a slight difference in age gave the older larks a great advantage in securing food from the parents; and the fact that food was more plentiful later in the season than at the beginning.

Length-growth curves show a precipitate rise during the first three days, a slight leveling during the next three days, and a precipitate rise during the sixth, seventh, eighth, ninth, and tenth days. The cause for the intermediate leveling is not understood, but the rise toward the end of the nesting period is brought about by the growth of the tail.

In the early breeding season the enemies of the young are weather and a scanty food supply. The weather may result in snows that bury them from sight. The scanty food supply may result in the starvation of one or more of the nestlings. Starvation results from the automatic feeding reaction of the adults wherein the nestling nearest that part of the nest habitually approached by the adults will receive the first feeding; if the food is scanty this bird will receive all or nearly all the food.Only when food is so abundant that the first nestlings fed do not swallow promptly will the remainder of the brood be fed. In this case food is withdrawn from the mouth and put in the next and so on. The female lark rarely brings more than will go into one mouth; the male may feed two or more, but never four or five, at a time. Those young larks that have a few hours' advantage in hatching--a full day in several cases in the early spring--will have the advantage in size that will allow them to push to that side of the nest over which the food always comes. They survive; the others may perish. Such occurred in many observed nestings in April.

Predacious enemies cause a greater and greater loss as the season advances into June and July. The optimum season for the welfare of the young is shown to be May.

One case of cowbird parasitism was observed and followed. A lark, which hatched before the cowbird, came to maturity. The cowbird probably did not. It suggested that the early nesting season and the exposed habitat may mitigate against such parasitism as may also the early departure of the young larks from the nest. However, since the adult lark will tolerate the parasitism and the food of June and July is suitable, other reasons prevent more extensive parasitism at this later season.

The young leave the nest, normally, on the tenth day, some three to four days before they can fly. Their protection during this interval is silence and a very effective "freeze" or crouch-concealment. Their plumage is remarkably adapted for this. The actions of the parents, especially the female, with her abandonment concealment, are calculated to take advantage of the protective color of nest and young at all ages.

Young leave the nest usually by following a parent that has brought food. One case was noted wherein a female enticed a belated nestling from the nest with a food morsel. The young fly in about five days after leaving the nest. They hop for some days after nest leaving, whereas the adults walk. This hopping may be anatomical or an atavism.

Plumages.--The recently hatched nestlings are rather heavily covered with down, a necessary protection against sun and cold in their exposed location. The down is cream-buff in color. At nest-leaving age the young lark is in full juvenal plumage but presents an appearance quite unlike that of the adults; each feather of the upper surface has a triangle of brown at its tip, the under surface is white except the throat, which is gray. ***

Food.--McAtee (1905), in his extensive account of the food of the horned larks, writes that in August and September many grasshoppers are taken (7.1 and 8.9 percent of the total food, respectively) and that weevils constitute 18 percent of the food in August. He says further that spiders are taken in every month. The conspicuous weed seeds that he lists (foxtail grasses, smartweeds, bindweeds, amaranth, pigweeds, purslane, ragweed, crab and barn grasses) are probably largely consumed in fall, winter, and early spring. The total of 79.4 percent of vegetable matter taken in the year, as given by McAtee, is made up largely of these weed seeds. He found about 40 percent of food taken in August to be animal matter, 20 percent animal matter in September, between 10 and 20 percent in October, 5 percent or less in November, about 2 percent in December, 1.73 percent in January, and 3.11 percent in February. The animal matter of January and February consisted principally of weevils and cocoons of tineid moths. Grain, chiefly waste oats, corn, and wheat, formed 12.2 percent of the food of larks, exclusive of California forms, and much of this would have been taken in the period under consideration.

The Main Subdivision at Evanston, where the most extensive observations were made by the writer, had, in winter of 1925-26, great quantities of Agropyron repens (quack grass), Seteria (foxtail), and Amaranthus (pigweed), all of which had been allowed to mature seeds. Of this the seeds of the quack grass were eaten first and wherever their long stems had fallen over the sidewalks the larks would invariably be found in January and February. When quack grass failed, foxtail was eaten, and lastly Amaranthus was substituted when no other seeds were available. Once or twice larks were noted along the roads feeding on the oats of horse droppings, when snow covered all the weed seed of the subdivision. And again at Ithaca the compost heaps, put out for fertilizer along the garden margins, supplied some food when snow lay deeply over the ground.

At Ithaca, during the spring of 1928, prairie horned larks were observed feeding on Setaria (March 1), on Ambrosia artemisiaefolia (April 1). A pair of larks were frightened away from an arctiid moth larva (Apatensis arge), which I observed the female dig up (March 3). Finally a few adults were collected in March at Ithaca (Connecticut Hill), and examination of the stomachs of six individuals showed that the vegetation consisted of oats, Setaria, Ambrosia artemisiaefolia, and waste buckwheat.

In summary of the feeding habits of the prairie horned lark in autumn, winter, and early spring, all that need be said is that the bulk of food taken is that of weed seeds, and the animal food, a much smaller proportion, is almost entirely of those forms harmful to the agriculturist. The lark, in feeding habits, finds for his food those things that appertain to the waste lands he inhabits.

Behavior.--Breeding birds, such as females in abandonment concealment of the nest, or males in flight song, exhibit several distinct flights, but at other seasons the flight is of but one definite character. This is a choppy undulation brought about by three or four rapid, even strokes of the wings interrupted by the space of about two beats during which the wings are closed. A note is uttered on the climb of each undulation. Or again, on prolonged flights, the character of the wing beat is as follows: Long strokes are made, one, two, three (or one, two), with a pause of about one wing beat between each stroke wherein the wings are folded. Then comes a pause of the length of one or two beats, with wings folded, causing a drop in elevation. These repeat. The bird goes thus: jump, jump, jump, climb (call also), drop, jump, jump, jump.

Voice.--The horned lark, like the goldfinch, usually advertises itself in flight by a definite, unmistakable note. Except for an occasional song, this is about the only sound from the birds in fall and winter. The flight and call notes are several in number, some of them appertaining more especially to the breeding season than to wintering birds, and in that connection they will be considered again. The chief stock in trade of the lark and the one most commonly heard is p-seet or merely zeet. It is uttered casually on the climb of the ordinary undulating flight, especially on long journeys or in flights of young birds. Adults frequently make low flights over the ground without uttering a note. This p-seet is occasionally, sometimes frequently, lengthened to p-seet-it during the flight. When flushed the note is zu-weet or zur-reet (long drawn), zeet-eet-it, or zeet-it-a-weet, which is so high pitched and mournful in character that it makes the birds indeed a part of the winter's gale that whips them away.

The season of song extended, in the Evanston region, from mid-January until early July; in the Ithaca region, from mid-February to late in June. With flight songs used for criterion, it was found that May was the optimum month. The lark sings both from the ground and in the air, under all conditions or weather, though flight songs are most numerous on quiet, mild days, perhaps a little more numerous when the sky is overcast than when it is clear.

The most vigorous period of song extends through nest building, egg laying, and incubation. Perhaps of this period that portion of it when the female incubates allows most song from the male, since he attends the female carefully during nest building and egg laying. The period of least song occurs when the young are in the nest, for the male assists in feeding. Ground songs are regularly distributed throughout the entire day; flight songs seem to be most numerous toward noon or near sundown.

For three months the prairie horned lark is the only singing bird in the open field; but with the coming and establishment of other migrants late in May and in June many other songs will be heard in that region. On June 16, 1926, at Evanston, the prairie horned lark, the last to begin singing that morning, went into flight song at 4:00 a.m. However, the lark almost always closes the singing at night with a long period of recitative which in mid-June would not close until after 8:00 p.m.

The literature contains several descriptions of the flight song of the prairie horned lark, that of Langille (1884) seeming to be most accurate. He describes the flight. The song he describes as "quit, quit, quit, you silly rig and get away." This is the intermittent type; nowhere in the literature has a description of the recitative been found.

Songs are sung from the ground, from a clod or any other slight elevation, the greatest elevation noted being the roof of a sample apartment put up on the Evanston area, and from the air. The ground songs are similar to flight songs though rarely as long or as systematically presented. The urge to flight song may come at any time or after an invading male lark has been evicted from occupied territory. Larks will also go into flight song upon approach of a human being or they can be forced to go up by driving them for a time about their territory.

The climb to flight song is distinctive and usually executed without a sound from the bird. The songs, in the air, are of two types: a recitative or rapid monotony of notes usually uttered at the beginning of the flight song, though occasionally at other periods, never over a few seconds in duration, accompanied by a steady beat of the wings; and an intermittent song uttered while the lark sails, about two seconds in duration, followed by a somewhat longer silent period during which the lark flutters up. The recitative can be transcribed as pit-wit, wee-pit, pit-wee, wee-pit; the intermittent as pit-wit, pit-wit, pittle wittle, little, little, leeeeee. Large circles are described overhead during the flight song, or the bird heads into the wind if it is strong. The lark closes flight song by a headlong drop to earth with wings tightly folded.

Female larks seem to be unaware of the males in flight song, though other males note the bird overhead. The territory a bird may occupy in flight song is very extensive. Never were two visible birds noted in such a performance simultaneously. The one in the air is left undisturbed though his performance may carry him over many other lark breeding grounds below. Breeding territories are not vertical for a distance above a few feet; the flight song territory is something quite different.

Of several methods employed to determine the heights of larks in flight song, the most accurate was found to be the use of a binocular with an ocular scale. It was determined thus, through measurement of 25 songs, that the lark sings from elevations that vary from 270 to 810 feet. The average was 464.4 feet. Differences in height seemed to be individual variations or due to weather. Thirty times flight songs varied from one minute to five; the average was 2.34 minutes. Intermittents, regularly given, averaged 11.9 a minute.

An Evanston bird sang from song posts on the ground, which, during one entire day, varied a few feet from the incubating female out to 100 yards. The average was 38.66 yards. Ithaca birds, with bigger territories, sang frequently as far as 150 yards from the nest.

Fall.--Young larks flock shortly after nest leaving. If the breeding ground has become untenable owing to vegetation, they seek other regions. Flocks grow larger through addition of adults in August and September and then smaller as migration begins. In flight the flocks are comparatively compact, but they spread widely when the birds alight to feed or pass the night. During autumn and winter they occupy regions essentially like those in which they breed in March and April, that is, semibarren or almost denuded areas, which may be natural or due to some seasonal condition of agriculture. The Lapland longspurs and the shore larks (Octocoris alpestris alpestris) are the only other birds that occupy a habitat with conditions just like those in which the prairie horned lark occurs in fall and winter.

Horned Lark* Eremophila alpestris [Prairie Horned Lark]

*Original Source: Bent, Arthur Cleveland. 1942. Smithsonian Institution United States National Museum Bulletin 179: 342-356. United States Government Printing Office