Contributed by Robert Leo Smith
[Published in 1968: Smithsonian Institution United States National Museum Bulletin 237 (Part 2): 725-745]
*The following subspecies are discussed in this section: Ammodramus savannarum pratensis (Vieillot), A. s. floridanus (Mearns), A. s. perpallidus (Coues), A. s. ammolegus Oberholser. Most of this account is based on the author's study of the eastern race of the grasshopper sparrow (Wilson Bulletin, 1959, 1963). Alexander Sprunt contributed a brief account of the Florida grasshopper sparrow, but kindly consented to withhold it so that all subspecies could be incorporated into the one account.
Although the grasshopper sparrow, Ammodramus savannarum, ranges from the Atlantic Coast to California and from southern Canada to southern Florida, Arizona, and Mexico, it is one of our more obscure birds. It is seldom noticed, even by those who are familiar with other birds. It usually keeps well hidden in the depths of the grass, and when pursued it flies only when nearly tramped upon. Its courtship, nest building, and rearing of young are carried on in a grass world of its own, well hidden from human eyes. Its song so closely resembles the stridulations of the grasshopper that many persons do not recognize it as a bird song.
The eastern race, A. s. pratensis (Vieillot), is found from the northeastern Atlantic seaboard through the tall grass prairie country to eastern Oklahoma and northeastern Texas, and from extreme southern Ontario and Quebec to central North and South Carolina, central Alabama, and Georgia. Thomas Burleigh (1958) writes that the birds nest locally in northern Georgia where grassland farming makes more habitat available. In recent years they have been found breeding south of the fall line in Macon County.
The western race, A. s. perpallidus (Coues), ranges from western Ontario, Minnesota, western Oklahoma, and central Colorado west to the Pacific Coast, and from the extreme southern prairie provinces of Canada south through eastern Washington and Oregon to central Nevada and southwestern California. So much of its habitable range is broken by mountains and deserts, its distribution is very spotty. The bird, however, may be more common than supposed, its absence in many regions reflecting the absence of observers rather than birds. D. W. Johnston (1949), who collected the first grasshopper sparrow in Idaho in 1947 in Latah County, writes (in litt.) that "here, too, it seemed to me that the birds were not unduly rare, although there had been much ornithological field work in the area previously."
The Florida grasshopper sparrow, A. s. floridanus (Mearns), inhabits the Kissimmee Prairie region. It was described in 1902 by Edgar A. Mearns, who based his description on a pair of birds collected on the Kissimmee Prairie near Alligator Bluff, Osceola County. Not until a quarter century later were additional specimens collected. According to W. H. Nicholson (1936) its range begins at a point 20 miles southwest of St. Cloud and extends to Okeechobee City. D. J. Nicholson writes that the center of abundance of the Florida grasshopper sparrow is "from 7 to 10 miles west of Kenansville, Osceola County, Florida, on the Kissimimee Prairie to within 10 miles of Bassenfer, Okeechobee County, Florida." The species does not breed over all the area, but forms scattered colonies, sometimes 30 miles apart.
An interesting situation occurs in the wide territorial gap between the ranges of pratensis and floridanus. David W. Johnston writes that the species' absence from the coastal plain is difficult to account for, as "much of this physiographic province has been converted to grassland. My only explanation is historical, namely the possibility that this species simply has not yet had time to invade or perhaps to develop a physiological toleration of the climatic conditions there." Also isolated on its breeding area is the Arizona grasshopper sparrow, A. s. ammolegus Oberholser. This race, described by H. C. Oberholser (1942) from a series of breeding specimens collected by Alex Walker in 1932, breeds in central southern Arizona, chiefly in the Huachuca Mountain region.
The grasshopper sparrow is a grassland bird, most plentiful in managed grasslands and absent from fields with 35 percent of the area in shrubs. They inhabit small grain fields to a limited extent, but their densities in such areas are a fraction of those found in grassland. Johnston and Odum (1956) observe that the grasshopper sparrow and the meadowlark (Sturnella magna) are the only true grassland species of the Athens, Ga. area, and in fact of most of the southeastern United States. Alden Miller (1951) writes that it is confined exclusively to grassland formation in California.
The eastern race appears to be most abundant on cultivated grasslands, particularly those containing orchard grass (Dactylis glomerata), alfalfa (Medieago sativa), red clover (Trifolium pratense), lespedeza (Lespedeza spp.), all of which form the clumps the species seemingly requires. Old fields of poverty grass (Danthonia spicata), dewberry (Rubus spp.) and broomsedge (Andropogon spp.) also are inhabited by the grasshopper sparrow, but the birds leave as the shrubs fill in the fields. On the islands off the New England coast this bird is found in old fields with red cedar (Juniperus virginiana) and bayberry (Morella pensylvanica).
Prime habitat for the western subspecies perpallidus and ammolegus is the prairie. Kendeigh (1941) notes that grasshopper sparrows are more plentiful in prairie grasses than in bluegrass.
In the forested regions of the east grasshopper sparrows originally were restricted to extensive natural clearings and sparsely wooded areas. They are found in such situations today in Minnesota (Roberts, 1936) and Michigan (Walkinshaw, 1940). Walkinshaw writes: "In Crawford County in natural clearings, grown sparsely to grass, the species was found on open areas only a few acres in extent where no stock was pastured and no haying was done. Here the birds were found in the natural wild state before man had taken over the land for his use.
Clearing the land for agriculture permitted the species to spread. Todd (1940) writes: "Undoubtedly the species has greatly increased in number during the past century and it is interesting to find that in extending its range it has invaded territory far beyond its usual altitudinal and faunal limits." Forbush (1929) notes that the grasshopper sparrow is a bird "of the coastal plains, river valleys and lower uplands. It is rarely found at elevations much above 1,000 feet." But in Pennsylvania on the western flank of the Alleghenies, the species is found at elevations over 2,000 feet when local conditions are suitable, and Maurice Brooks (1944) found it in West Virginia "on the Allegheny Backbone, in Pocahontas County, at an elevation of 4,300 feet."
The Florida grasshopper sparrow occupies an aberrant type of habitat for the species. Howell (1932) writes that this race "lives among the stunted growth of saw palmetto and dwarf oaks (Quercus mimina) a foot or two high, seemingly preferring this habitat to the grassy areas." D. J. Nicholson writes it inhabits the more open parts of the Kissimmee Prairie "where the saw palmettos are small--10 to 15 inches high--and the grass is sparse with patches of bare ground showing here and there. . . . they avoid heavy growth of palmettos or dense grass. . . . Frequently the cattlemen burn the prairie, and the birds seem to prefer these burned-over areas where the cover is very light and rather open."
Spring.--The grasshopper sparrow returns to its nesting grounds, often unnoticed, usually from mid-April to early May, although it may appear as early as the last of March. My earliest arrival date for north central Pennsylvania is Mar. 31, 1945, when a resident male returned to his old territory on the study area. A second male arrived two days later, but a short cold spell delayed the arrival of the rest of the population until April 12.
Cruikshank (1942) states that the species arrives in a marked wave about New York City during the first week of May, and stragglers pass through as late as the first week of June. I have never observed any marked wave in central or western Pennsylvania; there a few birds appear first, then the population builds up over a period of 1 to 2 weeks. My observations indicate that the first arrivals are males. They generally do not appear on the nesting areas until the grass is tall enough to conceal them.
Territory.--Upon arrival at their nesting grounds, male grasshopper sparrows undertake territorial establishment. The first arrivals have the area to themselves and generally confine their singing to the morning hours. As more birds return, territorial activity increases in intensity, reaching a climax about 2 to 3 weeks after the first birds arrive. Then song is heard throughout the day.
The male proclaims territory by singing the "grasshopper" or territorial song (see Voice). When engaged in a song duel, the male alternates song with display. Crouching with head lowered between the shoulders, he raises and flutters one or both wings. Then after hearing the song of his neighbor, he stands erect and sings back. The song completed, he again crouches and flutters his wings while his rival sings. The wing fluttering, conspicuous only during territorial establishment, is never accompanied by a song or a call, and is confined to the intervals between songs.
I regard the wing fluttering of the grasshopper sparrow as a hostile display. During the period of territorial establishment the song of a rival is a sufficient stimulus to release it. Often the birds are hidden by the vegetation or the topography of the field so they cannot see one another. They sense the presence of a rival by the sound of his song and manifest this by a hostile display, as if the rival were nearby in the grass.
I have never observed a territorial dispute that elicited an intimidation display of high intensity, although some could have taken place in the grass, out of sight. The only physical encounters I observed during hundreds of hours spent with the species occurred after a bird saw another invade its aerial territory. In each instance the bird chased the intruder, then retired to a singing perch, fluttered his wings, and sang the grasshopper song. I have witnessed a number of such clashes at disputed boundaries. Since the deep grass conceals territorial infringements on the ground, this mode of defense could be most important. Perhaps the grasshopper sparrow recognizes the limits of its territory only from a grasstop point of view.
The territorial "grasshopper" songs usually are delivered from the highest perches in the territory. These may include a clump of grass, an alfalfa stalk, a tall weed, a small bush, fence post, utility wire, tree, or farm equipment left in the field, hay cocks, or grain shocks. The birds appear restricted to low perches only by their habitat, and use low ones simply because no higher ones are available. This was demonstrated experimentally. When a wooden stake tall enough to stand two feet above the grasstops was placed in a bird's territory, the bird claimed it within minutes. When a still higher perch was introduced the next day, the bird abandoned the first for the new, higher perch.
Song perches are clustered about certain singing areas, usually near the periphery of the territory, apart from the nesting areas. Among the birds I have studied, singing perches were from 165 to 412 feet from the nest. Their position may be influenced by row crops in the territory when grasshopper sparrows then confine their singing perches to the vicinity of grass plots.
The size of 22 territories plotted on my study area ranged from 1.2 to 3.3 acres; 11 were between 1 and 2 acres, 9 between 2 and 3 acres, and 2 were over 3 acres. Their average size was 2.03 acres. Kendeigh (1941) reports the average size of 6 territories was 3.4 acres.
Territorial boundaries are maintained rigidly during the periods of territorial establishment, nest building, and incubation. After the young hatch, territorial defense declines and considerable movement of birds into other territories occurs. The movement is often initiated by young birds just able to fly, that flutter into adjoining territories where the parents follow in answer to the feeding call.
Prior to second nesting, territorial defense increases sharply for 2 to 3 days. The males sing the "grasshopper" song and flutter their wings. Territorial boundaries may be shifted in response to disturbances made by harvesting of hay and small grains. In one instance a male grasshopper sparrow shifted his territory for the second nesting to include the eastern half of his neighbor's territory. The hay on this portion had been mowed early, and new growth afforded cover lacking in the original territory. The neighboring male in turn took over the western half of the first male's old territory. In the end both birds had new growth and newly mowed hayfields in their respective territories. Interestingly, these two birds occupied approximately the same territories the following year. Another male, whose territory was bisected by a strip of field corn, took over a corner of his neighbor's territory when the increasing height of the corn walled off the lower half of his own territory and made it useless.
After the second broods leave the nest, grasshopper sparrows no longer defend territorial boundaries, although adults and young remain in the general vicinity until they disappear in the fall.
Courtship.--Within 10 to 14 days after their arrival, the males introduce the sustained song (see Voice), which for a short time almost replaces the grasshopper song and signifies that courtship is at its height. Most courtship activity is hidden in the grass, but occasionally a male rises above it on quivering wings, delivers this song in a low fluttering flight, and then drops out of sight again. The female may answer this song with a trill of her own (see Voice), which she often sings alone. The male responds by singing the sustained song or by flying to her. At times the male pursues the female and sings the sustained song as he gives chase.
W. H. Nicholson writes that the male Florida grasshopper sparrow "has a fluttering mating flight similar to that of the seaside sparrow except that it is low, 3 to 5 feet above the ground for 50 to 100 feet; upon alighting on a twig or saw palmetto it bursts into song."
Nesting.--Nests of the grasshopper sparrow are extremely hard to find. During the course of my study I was able to locate only four. All were hidden at the base of clumps of grass, alfalfa, clover, dead vegetation, or other cover, and often had one or two paths leading to the entrance. The nest itself is built of stems and blades of grass and lined with fine grass and rootlets, occasionally with horsehair (Burleigh,1923; Simmons, 1925; Trautman, 1940). Sunk in a slight depression, the rim is level with or slightly above the surface of the ground. The top is usually arched or domed at the back, giving it an ovenlike appearance. Nest measurements range as follows: outside, 4.50 to 5.50 inches; height, 2 to 2.25 inches; inside, 2.50 or 3 by 3.25 inches; inside depth, 1.25 to 1.30 inches (Simmons, 1925; Dixon, 1916).
W. H. Nicholson (1936) describes the nest of the Florida grasshopper sparrow as follows: "Many of the nests were a single dead palmetto leaf without any other vegetation to conceal them; others were under dead drooping palmetto leaves with small dwarf oaks and wire grass growing on all sides, while several others were in thin tussocks of dead wire grass which looked too small to hide the bird, much less the nest." Nests were "lined with fine wire grass and arched over with grass blades."
Nest-building of the eastern and western grasshopper sparrows reaches its height in late May. This is followed by a second nest-building period in very late June and early July. D. J. Nicholson writes that the nesting of the Florida grasshopper sparrow begins "about the middle of April to the first week in May; second nestings are begun about the first of June; and again in July they breed a third time."
Eggs.--The grasshopper sparrow commonly lays 4 or 5 eggs; although frequently sets of 3 are found and occasionally as many as 6. They are generally ovate and have a slight gloss. The ground color is creamy white, speckled and spotted with shades of reddish browns such as "Rood's brown," "russet," "Mars brown," or "chestnut brown," and undermarkings of "pale purplish gray," or "pale neutral gray." The spots are usually sharp and well defined; they may be scattered over the entire egg or concentrated toward the large end where they often form a loose wreath or become confluent over the cap. Many eggs show as many gray undermarkings as spottings of the red browns. The pattern of markings of this species might be considered somewhat delicate, especially as compared with the eggs of the Savannah or song sparrow. The measurements of 92 eggs average 18.7 by 14.4 millimeters; the eggs showing the four extremes measure 20.8 by 14.7, 18.3 by 15.8, 16.3 by 13.7, and 17.9 by 13.6 millimeters.
A. s. pratensis. The measurements of 50 eggs average 18.6 by 14.4 millimeters; the eggs showing the four extremes measure 20.8 by 14.7, 18.3 by 15.8, 16.3 by 13.7, and 17.8 by 13.7 millimeters.
A. s. perpallidus. The measurements of 32 eggs average 18.7 by 14.3 millimeters; the eggs showing the four extremes measure 20.3 by 15.0, 19.6 by 15.2,17.8 by 14.2, and 17.9 by 13.6 millimeters.
Incubation.--The exact incubation period of the grasshopper sparrow is unknown, as it is only with considerable luck that a nest with a partial or a recently completed clutch can be found. King (1940) reports finding a nest on May 29, 1940, containing five eggs. On June 10, the same nest contained four young and one egg. Assuming that the young were shortly out of the egg and the fifth had yet to hatch, the incubation period would have been 12 days. D. J. Nicholson writes that the incubation period of the Florida grasshopper sparrow is "11 to 12 days--not more." Simmons (1925) writes that the incubation period of perpallidus "lasts for about 12 days."
The female alone incubates the eggs and broods the young. She sits very closely on the nest. When leaving, she slips off, runs a distance through the grass and then flies. On her return she never flies directly to the nest, but drops down into the grass some distance away and goes to it on foot, by one of the several paths.
If flushed from the nest the female may dart off, run a short distance, arise in a short fluttering flight, then drop to the ground again where she spreads her tail and trails her wings as if injured. At other times the female may flutter directly off the nest as if crippled or may fly from the nest to a point 25 to 30 feet away and hide in the grass.
W. H. Nicholson writes that some female Florida grasshopper sparrows "will run off the nests before they are found; others will sit tightly until almost stepped upon before they flutter off uttering weak squeaking notes not unlike a mouse." He (1936) writes further: "When they did leave they did not fly, but ran off dragging tail and fluttering the wings as if crippled. If followed they would lead the intruder off about twenty feet from the nest and then fly to some nearby palmetto and begin scolding. Several times the bird would run along the ground within eight feet of me scolding with a weak tik-tik-tik."
During the incubation period the male spends his time singing and defending the territory, but shows little concern over human intruders. When they appear he simply stops singing and hides in the grass. The actions of both sexes are such that they attract no attention to the nest location.
The behavior of both male and female changes after the young hatch. One male I observed sang both songs throughout the day his young hatched. The female flushed from the nest but did not feign injury. She flew a short distance, hid in a swath of hay and chipped softly. The male chipped several times, broke into the grasshopper song, fluttered both wings, and then continued to chip vigorously. As I left the area the male sang the sustained song, interrupted it with a grasshopper song, followed by the trill (see Voice).
Young.--Grasshopper sparrows at hatching are blind and covered with grayish-brown down. Walkinshaw (1940) gives the weight of young at hatching as between 1.7 and 2.3 grams. This is approximately the same weight as the egg. At 4 days wing feathers break through the sheath; breast and side feathers still are in the sheath; back, belly, and rump are bare. At 6 to 7 days body feathers emerge from the sheath and appear dark brown to blackish with yellowish buff edge. A distinct buffy crown patch is present; the commissure is bright yellow. By day 9 to 10 the young are well feathered, though the tail feathers are still short. Walkinshaw gives the weight increases as of the second day, 2.9 grams; sixth day, 8.7 to 9.1 grams; and seventh to eighth day, 9.7 to 10.5 grams. Wetherbee (1934) reports the weight of 14 immature birds as ranging between 14.0 and 18.3 grams, averaging 16.09.
Upon my approach to the nest the young invariably gaped for food, but expressed no sign of fear. On June 7, 1944, my dog discovered the nest of one pair and threw two of the four out of the nest. As I replaced these, the two in the nest gaped for food. Later in the day, immediately after the female fed the young, one bird gaped and three did not respond. This same pattern was followed at other nests. Recently fed young did not respond in any way; if hungry they gaped when I moved near the nest.
Young birds on my Pennsylvania study area remained in the nest 9 days. Michigan birds observed by Walkinshaw (1940) remained in the nest the same length of time. When out of the nest, the young run mouselike through the grass and rarely appear above the grasstops.
Both male and female are very solicitous about the young. During incubation the birds exhibit little concern about human and animal intrusions in their territories except those of cats. After the young hatch, the birds react to human intrusion with vigorous alarm. They may fly in wide circles above the trespasser, raising their crest feathers and flicking their wings and tail. On the ground they bob up and down on their legs like a spotted sandpiper (Actitis macularia) and utter a sharp chi-ip. When highly alarmed they give this double note so rapidly it almost runs into a trill. Often the male will interrupt his chipping to break into a grasshopper song. If the birds are carrying food to the young at the time, they invariably eat the insect and continue their alarm behavior. When a dog enters the territory, the birds drop into the grass, crouch low, and remain silent until the animal passes.
Plumages.--The juvenal plumage and post-juvenal molt of the grasshopper sparrow have been studied in detail by George M. Sutton (1935, 1936). He found a number of discrepancies in the descriptions by Dwight (1900), which were apparently based on a poorly aged specimen.
According to Sutton, the natal down is replaced by the juvenal plumage in a complete postnatal molt. It is worn for a short time as a complete plumage and is probably complete at 10 to12 days of age. At this time the rectrices are stubby; the feathers of the back and scapulars are plain dark olive-brown or blackish brown, edged with buff, and totally lack any sort of russet spots on the tips. Richard R. Graber (1955) describes the juvenal plumage in detail as follows:
"No sexual dimorphism. Forehead and crown streaked, brown and black, with median and superciliary stripes of light buff or buffy white. Nape mottled, buffy white and black. Back, feathers black, edged with buff or buffy brown. Upper tail coverts black, edged with buff. Rectrices black, narrowly edged with buff, except median pair (broadly edged). Remiges slate gray or black, edged with buff or buffy brown. Tertials black, edged with white. Superciliary buffy white, streaked with black. Auriculars buffy brown. Post-auriculars concolor with nape. Under parts white or buffy white more strongly tinged with buff on chest, sides, flanks, and crissum. Upper chest rather sparsely streaked with blackish or dark brown. Other under parts unmarked. Stub-tailed birds much darker throughout than older birds."
The post-juvenal molt, according to Sutton (1936), takes place in late June or early July with the young of the first brood. Second and third brood young may be wearing part of the juvenal plumage as late or even later than mid-September. The body feathers of the juvenal plumage are lost first, while the flight feathers and tertials may be held for a longer period. At 20 days russet-tipped feathers appear on the back; the superciliary line still is sharply streaked; the rectrices are sheathed at the base. At 4 weeks the juvenal feathers are lost on the crown and the superciliary line, together with all remaining body feathers lacking russet tips. At 36 days the buff-margined juvenal feathers are practically gone, replaced by buffy feathers on the chest, sides, flanks, and lower throat. The back is thickly set with incoming fully-sheathed feathers, and new lesser wing coverts with a strongly yellowish cast appear. At about 6 weeks the juvenal rectrices are lost almost simultaneously. The molt of the juvenal primaries starts from the innermost outward.
A dull yellow superciliary is present in some juvenal males, but apparently is absent in juvenal females. The yellow superciliary spot is acquired by both male and female birds with the post-juvenal molt in the latter part of summer and fall, and not in April with a partial prenuptial molt as described by Dwight (1900).
The first winter plumage contains no streaked feathers on the chest. The back feathers are black with apical chestnut spots edged with pearl gray. The median crown stripe, edging of tertiaries and wing coverts, sides of the head, superciliary line, and under parts are rich buff. New feathers above and in front of the eye are deep yellow. The neck feathers are red-brown medially. Middle of the abdomen is pure white.
There is no evidence of a prenuptial molt except for replacement of feathers lost accidentally. Sutton (1936) states that "the large majority of spring birds are exactly like fall adults except that the plumage is a little more worn. Fall birds are beautifully fresh, breeding birds are noticeably worn, late summer birds are very decidedly worn, and spring birds are in an exactly intermediate position between fall and summer."
The second winter plumage is acquired by a complete postnuptial molt. According to Dwight (1900) it differs little "from the first winter dress, the buff less obvious and the colors deeper."
The adult western grasshopper sparrow, A. s. perpallidus, is paler and grayer than the eastern race, with more chestnut and rusty brown and less black above.
Oberholser (1942) describes the Arizona race as similar to A. s. perpallidus. The upper parts are decidedly paler, with more chestnut and rufous and also with much less, sometimes almost no, black on the back. The lower parts are lighter and not so dull.
The Florida race, A. s. floridanus, is much darker above than A. s. pratensis, paler and less buffy below. Feathers of the upper parts are mainly black, edged with grayish, with little or no brown. The under parts are less heavily washed with pinkish buff than A. s. pratensis.
Food.--Insects form the staple food of the grasshopper sparrow; and the most prominent among these is the grasshopper. Judd (1901) found that grasshoppers (genera Xiphidium, Scudderia, Hippiscus, and Melanopus) formed 23 percent of the bird's food during eight months of the year, 60 percent of its food in June and 37 percent of its diet from May to August. Thus the name of the bird is appropriate from the standpoint of its diet as well as its song.
Judd examined 170 stomachs of this sparrow collected between February and October from both the east and west. Food consisted of 63 percent animal matter and 37 percent vegetable matter. Insects comprised 57 percent of its total food, spiders, myriapods, snails, and earthworms, 6 percent; harmful beetles made up 8 percent and caterpillars 14 percent. Beetles were of three families: click beetles (Elateridae), weevils (Sitones and related genera), and smaller leaf beetles (Systens spp). Judd writes: "Caterpillars are eaten more freely in May than at any other time, and constitute 33 percent of the food of that month. More than half of the caterpillars destroyed are cutworms. In one stomach from Bourbon County, Ky., were six cutworms (Nephelodes violans), each an inch long. The army worm seems to be also a favorite article of diet. Eleven percent of the total food consists of ants, dung beetles (Atoeniys and Apodius), and 1 percent bugs, including leaf hoppers (Jassidae), leaf bugs (Capsidae), assassin bugs (Reduviidae), and smaller soldier bugs (Hymenarcys and Trichopepla).
Vegetable food consists of grain, chiefly waste, 2 percent; wood sorrel (Oxalis) 2 percent; ragweed (Ambrosia) 5 percent; pigeon grass (Setaria), panic grass (Panicum), and others 17 percent; smartweed (Polygonum), purslane (Portulata), ribgrass (Plantago), and sedges (Cyperacease) 11 percent.
Howell (1932) writes of the Florida race: "Examination of the stomachs of 10 specimens taken on the Kissimmee Prairie showed the bird's food to consist of animal matter (insects and spiders), 69 percent, and vegetable matter, 31 percent. The insects taken in greatest quantity were grasshoppers and crickets, beetles, weevils, and moths and their larvae, with a few flies and bugs. Seeds of sedges composed most of the vegetable matter, with some grass seed and seeds of star grass (Hypoxis)."
Behavior.--The grasshopper sparrow is a secretive bird, difficult to observe. It seldom flies, but runs ahead of the searcher through the grass and flushes only when hard pressed. As William Brewster (journal) describes it: "when flushed the sparrows rise swiftly and vigorously, twisting a little. . . the flight then becomes steady and direct and is performed in long, regular undulations, the wings being vibrated rapidly." He adds: "On the ground they both run and hop." Witmer Stone (1937) notes that in flight the bird "turns to one side or the other like a snipe." Simmons (1925) writes that when flushed the western grasshopper sparrow rises "in a zig-zag flight for a few yards" and then "dives back into the weeds. . . . In open fields, flight is extended and rapid."
The bird perches in a peculiar crouched position, as if ready to dart off in an instant.
D. J. Nicholson comments on the colonial nature of floridanus: "They breed in small colonies--three or four to a dozen pairs. These colonies are very local and are not found everywhere over this vast prairie, many apparently suitable spots being unoccupied."
These same words might well apply to the eastern and western grasshopper sparrows as well, for they show the same colonial nature and fluctuate considerably in abundance from year to year.
One cause of population changes might be attributed to grassland management practices. On my study area, for example, the fields during the early part of the study were run down and supported a poor growth of timothy, alfalfa, and red clover. From 1944 on, the fertility of the fields increased considerably and the grass mixture was changed to a thick, vigorous growth of alfalfa, ladino clover, and brome grass (Bromus inermis). The grasshopper sparrows in the area settled in hay and abandoned fields where the vegetation was not so heavy.
Oscar Root (1957, 1958, letter), who kept a long-time record of local population fluctuations on a level, artificially drained airport of 100 acres at North Andover, Mass., found the grasshopper sparrow populations there built up to highs, followed by severe reductions in numbers the following year. He believed mowing the grass on the area prior to his counts reduced the population. However, when mowing was postponed to allow completion of nesting by the sparrows, the population still remained low. He states that certain areas always productive in the past were without grasshopper sparrows, though in prime shape and undisturbed.
The birds about Concord, Mass., have shown a similarly fluctuating pattern of abundance through the years (Griscom, 1949).
An unusual concentration of grasshopper sparrows is described by Brewster in his Nantucket journal. Here on June 27, 1874, he and Maynard found grasshopper sparrows extremely plentiful. He writes that "they were equally distributed for an extent of three to four miles. Often there were three or four pairs breeding in an area a hundred yards square." This species was fairly common on the Islands in the 1920's, but in recent years it has become local and uncommon and appears to have been replaced by the Savannah sparrow (Passerculus sandwichensis) (Griscom and Folger, 1948). Mrs. A. B. Davenport writes that the same situation is true on Conanicut Island, off Rhode Island. The bird was formerly abundant on Martha's Vineyard and north to Essex County, Mass.; today it is rare and local, replaced by the Savannah sparrow (Griscom and Snyder, 1955).
Thus it appears that populations of grasshopper sparrows fluctuate sharply at times in spite of the availability of suitable habitat. No reason can be given, but in some areas it appears to be giving way to the Savannah sparrow, a bird that occupies the same fields and is able to maintain its numbers when shrubs invade the area.
Of these the most familiar is the grasshopper song from which the bird derives its name. The song consists of one to three introductory notes followed by a long, very high-pitched trill. The length of this song varies from 1 to 2 1/5 seconds, and averages about 1 2/3 seconds. The pitch, according to Saunders, varies from F#7 to D8; and the pitch interval varies from 1 to 3 1/2 tones. The introductory notes are usually of lower pitch than the trill." The trill is simple and nearly always on the same pitch throughout.
Brand (1938) determined the pitch of this song to range from 9,500 to 7,675 vibrations per second, with a mean of 8,600. By contrast the frequency of a piccolo is 4,608 cycles per second.
The songs of the other races resemble closely those of pratensis. Zimmer (1913) describes the song of the western grasshopper sparrow as a pit-tuck zee-ee-ee. Simmons (1925) describes it as a "thin, wiry monotonous grasshopper like pit-tuck zee-ee-e-e-e-e-e-e-e-e-e or kalsick ha tsee-e-e-e- e-e-e-e-e-e-e-e."
W. H. Nicholson (1936) describes the song of the Florida grasshopper sparrow "as sounding like twittle-e-dee repeated several times in rapid succession with a tik-tik-tok-buzzzzzz at the finish. Many times I have heard them sing the latter part of this song without the former, but never the former part alone. The latter part has a distinct insect-like sound."
The sustained song is more elaborate and more musical than the grasshopper song and is subject to considerable individual variation. It ranges up to 5 seconds in length. The sustained song in its entirety consists of a grasshopper introduction followed by a sustained series of melodious notes. The song may be written as tip-tup-a-zee-e-e-e-e-e-e-e-e zeedle zee-e-e-e zeedle zeedle zee-e-e-e-e-e-e. The grasshopper introduction often is omitted, especially after territories are well established.
Jouy (1881) mistakenly attributed this song to Henslow's sparrow (Passerherbulus henslowii). He writes: "Besides their characteristic note of te-wick, they have quite a song which may be fairly represented by the syllables sis-r-r-rit-srit-srit, with the accent on the first and last parts. The song is often uttered while the bird takes a short flight upward; it then drops down again into the tangled weeds and grasses where it is almost impossible to follow it."
This is an adequate description of the sustained song of the grasshopper sparrow which is often given in flight. During 5 years of concurrent observations of both species in the same fields, I never heard a Henslow's sparrow sing a song that even remotely resembled the sustained song of the grasshopper sparrow.
The primary function of the sustained song is to attract and hold a mate. The grasshopper introduction, however, is hostile in character and serves as a warning early in the season. Later, when the grasshopper introduction is dropped, the males respond to the sustained song with a grasshopper song. Then both birds launch into a duel of grasshopper songs.
The least common vocalization of the male grasshopper sparrow is the trill. Unless one is frequently in the field among these birds, the observer is apt to miss it entirely. Walkinshaw (1940) calls it a nesting song, and Saunders (1951) describes it graphically. It can be written ti-tu-ti-tu-ti-i-i-i-i. The song consists of a series of moderately loud, short, alternate notes, given rapidly and ending in a downward trill. It is delivered on the ground or from a perch. The trill generally is not given until the pair is formed, and is then uttered only in the vicinity of the nest. It may follow one of the other two songs, or it may be given alone, often in answer to the female. This song apparently serves as a bond to hold the pair together, and as a signal to the female and young that the male is approaching the nest.
The female grasshopper sparrow has a song quite similar to the trill of the male, but softer, lacking the downward trill, and more suggestive of the song of the chipping sparrow (Spizella passerina). It may be written ti-ti-i-i-i-i-i-i-i. Its primary function is apparently to declare her presence on the territory to the male. She also gives the trill when she is approaching or is near the nest. When so used it serves to announce her location, to maintain the pair bond, and to signal both the male and the young that she is approaching the nest.
Song falls into seasonal and daily patterns. The male sings the grasshopper song from arrival until mid-August. The sustained song is introduced approximately at the time of the females' arrival. After pairing, the volume of song drops for a few days, but singing does not cease entirely. The sustained song is confined mostly to evening twilight; the grasshopper song is the common daytime song. During the periods of egg laying and incubation the male sings both songs frequently, especially in early morning and late evening, continuing until darkness. Song wanes during June when the birds are busy feeding young. Prior to re-nesting the sustained song is heard frequently for several days before it wanes again. The trills of both male and female are given from the period of pair formation to the completion of nesting.
The grasshopper sparrow does not have an extended morning awakening song. When it wakes the bird may start to feed in silence, or it may utter a few call notes, or snatches of the grasshopper or sustained songs. Once the bird starts singing, it interrupts the song sequence frequently with feeding. By mid-July the morning singing has almost ceased, and daytime song is rarely heard, but in the cool of evening, as feeding activity stops, twilight singing may still be heard until darkness falls. At this period the sustained song with its greater carrying power seems to be the most conspicuous, and for this reason has been erroneously described as a postseason elaboration of the regular song of the species. Night singing, particularly when the moon is full, is a common habit with all races of the species.
The call note of all races of the grasshopper sparrow most commonly heard is a two-syllabled chi-lip or til-lic. Given by both sexes, the call functions primarily as an alarm note; as such it varies in intensity. When rapidly given in high intensity alarm, the notes suggest the slow clicking of a fishing reel. Less frequently, especially under situations of low intensity alarm, the call note is only a sharp tik.
While feeding the grasshopper sparrow utters a single note tik or chip. It is similar to the alarm note, but is higher pitched and less sharp and vigorous. The food call of the young is a double note chi-ip similar to that of the adult but with a more liquid quality.
Field marks.--Adult grasshopper sparrows are short-tailed, flat-headed, and the only sparrows of the grasslands that lack streaks or markings on the breast. Young birds of the year have streaked breasts and are often confused with adult Henslow's sparrows, which are more sharply streaked with black on the breast, sides, and flanks. The young Henslow's sparrow with relatively unstreaked breast may be confused with the adult grasshopper sparrow, but the distinctly chestnut wings of Henslow's sparrow separates this species at all ages from the grasshopper sparrow.
The only other bird with which the grasshopper sparrow might be confused is Leconte's sparrow (Passerherbulus caudacutus). This sparrow, however, inhabits prairie marshes, an environment too wet for the grasshopper sparrow. Both adult and young Leconte's sparrows are streaked, but the under parts are light yellowish brown instead of cinnamon buff, and they lack the yellow before the eye and on the bend of the wing.
Enemies.--It is ironical that the grasshopper sparrow's greatest benefactor is also his greatest enemy. This sparrow depends upon its man for maintenance of habitat through grassland management but these fields are cut for hay. Haying usually begins in mid-June, the height of this bird's nesting season. The nest usually escapes destruction from mower blades, but some nests may be crushed by implement wheels. If the nest escapes destruction by haying operations, it is exposed to weather and predators. Grass used for silage is cut early, around the first of June. This is the height of nest building by the grasshopper sparrow. I have found that in fields regularly cut for grass silage, resulting in early loss of cover, the population of grasshopper sparrows is very low. The loss of cover later in the nesting season does not result in abandonment of the field or the nest, if the nest has not been destroyed. I have never noted grasshopper sparrows leaving a field after haying, despite the loss of cover. This is in sharp contrast to Henslow's sparrow, which leaves a field when the grass is cut.
Among the predators of the grasshopper sparrow are the skunk (Mephitis mephitis), weasels, spermophiles (Citellus spp.), foxes, and cats. Cats take their toll of grasshopper sparrows, especially after the hay is cut, although they probably catch fewer of these birds than of other sparrows. Dogs at times discover grasshopper sparrow nests accidentally.
W. H. Nicholson writes that hogs, snakes, spotted skunks (Spilogale ambarvalis), and striped skunks seem to be the major enemies of the Florida grasshopper sparrows. He states; "I have found 25 to 30 nests under construction; upon returning later I found practically all of them destroyed by the above."
As the nests are well concealed and the birds stay close to the grass, hawks probably are insignificant as predators, except after the hay is cut. Marsh hawks (Circus cyaneus), though common in grasshopper sparrow habitat, appear to have little influence on the species. The grasshopper sparrow apparently pays no attention to them, for I have observed males singing while marsh hawks were hunting nearby. When, however, a sharp-shinned hawk (Accipiter striatus) approaches, the grasshopper sparrows stop singing at once, give a few alarm notes, and drop into the grass. After the hawk has disappeared, they come out of hiding and resume their singing.
The cowbird (Molothrus ater) parasitizes a few nests of the grasshopper sparrow, but the incidence is extremely low. Friedmann (1938) lists three known occurrences of parasitism of the eastern grasshopper sparrow and three for the western race. Hicks (1934b) found one grasshopper sparrow nest containing a cowbird egg in Ohio. This low incidence reflects the difficulty cowbirds must have in locating nests of this species.
Walkinshaw (1940) observed small red ants attacking young birds in the nest and entering two pipped eggs. The female ate all the ants in and around the nest.
Terres (1939) reports that an immature grasshopper sparrow was caught in the vertical web of a golden garden spider (Miranda aurantia). The bird was released, apparently unharmed.
Fall and Winter.--By late August the nesting season is over, the young grasshopper sparrows are independent, and the adults are silent and more retiring than ever. The birds stay close to the grass and refuse to fly unless very closely pressed and when flushed quickly seek cover again. Unlike many other sparrows, they do not flock. During migration they may join other migrant fringillids, like the field and song sparrow, and appear in rather unlikely places. I have observed migrating birds along brushy fence rows, and I caught one immature individual in a trapping station in an elderberry thicket. By late September most grasshopper sparrows have left the breeding grounds, although a few may linger on until late October and early November.
Simmons (1925) writes that the eastern grasshopper sparrow during migration in the Austin region of Texas is found in "closely cropped pastures dotted with mesquite, floored with some stubble and buffalo grass, and edged with weed patches, brush thickets, weedy fence rows, and plowed ground."
Skinner (1928) writes that in the sand hills of North Carolina wintering grasshopper sparrows inhabit sandy grassy fields, especially those with broomsedge. Lowery (1955) states that this species is a "rather uncommon or at least seldom observed winter resident" in Louisiana, where it inhabits "broomsedge fields with a few small trees or brush piles." Tyler (1913) writes that in California wintering grasshopper sparrows inhabit "old weedy fields, weed-grown vineyards and berry patches."
There are few winter records north of the above range. Trautman (1940) reports a male bird found on Dec. 29, 1928, in the Buckeye Lake, Ohio, region with a "pathological condition present in the bill and feet, for both were considerably swollen and a toe was gone." Griscom and Snyder (1955) cite a winter record for Dec. 6, 1892, at Arlington, Mass. A grasshopper sparrow banded by Oscar Root at North Andover, Mass., on Nov. 30, 1940, was collected nearby on Jan. 19, 1941. Another bird was collected at Rose Blanche, Newfoundland, Nov. 27, 1950 (Peters and Burleigh, 1951a). Easterla (1962) records two, of which one was collected, wintering near Sedalia, Mo., Jan. 14, 1961.
The Arizona race, ammolegus, winters from northwestern
Mexico to Guatemala. The Florida grasshopper sparrow is resident
and remains on the breeding grounds all through the year.
Grasshopper Sparrow* Ammodramus savannarum
*Original Source: Bent, Arthur Cleveland and collaborators (compiled and edited by Oliver L. Austin, Jr.). 1968. Smithsonian Institution United States National Museum Bulletin 237 (Part 2): 725-745. United States Government Printing Office