Contributed by Wendell Taber and David W. Johnston
[Published in 1968: Smithsonian Institution United States National Museum Bulletin 237 (Part 1): 80-111]
The usual breeding range of the indigo bunting includes southern Canada and the eastern United States westward to Texas, Kansas, and Manitoba. Sporadic nesting and summer occurrences have been reported from a scattering of western states (A.O.U. Check-List, 1957). It is typically a species of forest edges, weedy fields, roadsides, shrublands, and brushy ravines. As Burleigh (1958) suggests, it is a bird of the "more open country, partially overgrown fields and slashings, hedgerows, and underbrush bordering roads. . . . [There is a] noticeable tendency for this species to be more numerous along the creeks and rivers where the woods are open and there are suitable thickets in which to nest." The male requires moderately high, open perches from which he can sing conspicuously. In sharp contrast, the female searches out the concealment of dense cover close to the ground.
Bond (1957), studying ecological distribution of breeding birds in the upland forests of southern Wisconsin, noted that indigos occasionally occur in the forest, but are generally a species of the more open drier woods. Several factors appear to govern their breeding distribution: decreasing canopy of the forest, decreasing moisture, decreasing sapling density, and increasing shrub density. Odum (1950) found that in the mountains of southwestern North Carolina these buntings were less numerous in mesic shrublands than in xeric shrublands where there were "numerous species of shrubs and small trees which occur in dense thickets interspersed with more open places dominated by grasses and herbs." Todd (1940), like Burleigh, believed that a habitat near water is preferred, even if the water is only a small mountain stream. In western Pennsylvania, however, dry hillside thickets and even orchards are often chosen.
In Maryland, Stewart and Robbins (1958) noted indigos in "hedgerows, wood margins, and orchards; also in brushy cut-over areas of swamp forest and of rich, moist forest on the upland." In north central Arizona, H. Dearing and M. Dearing (1946) found the species in an apple orchard on one side of a road and in native trees (pines, oaks, cypress, juniper) and shrubs along the road. The shrubs included Ceanothus, scrub oak, sumac, and two species of manzanita. Roberts (1932) found buntings in sparsely wooded brush country, clearings grown up in second growth, and narrow strips of timber bordering lakes and streams. In Louisiana, except for the coastal areas, Lowery (1955) recorded them in clearings at the edges of woods and along highway and railroad rights of way.
As it thrives in areas where the forest has been cleared and is at least partially reverting to its original state, the indigo bunting would be expected to increase in parts of its range where such conditions develop. In north central Florida, for example, agricultural practices have radically changed the landscape over the past few decades, converting much of the once extensive pine forests, hammocks, and swamplands to pasturelands. As some of the pastures are abandoned and undergo processes of ecological succession, the stage is set for their occupancy by these buntings. Before 1964 the species was rarely seen in the environs of Gainesville, but in that year breeding birds were found at 10 widely scattered sites. Its increase in recent years has been noted elsewhere in Florida by Sprunt (1954) and in Maryland by Warbach (1958). The comments of Wells (1958) are apropos: "Perhaps originally a bird of successional vegetation within the Eastern Deciduous Forest of North America, and of the oak openings along the prairie-forest ecotone, the Indigo Bunting was undoubtedly restricted in numbers by the relatively closed canopy of the climax forest. . . . In the East the opening of the forest canopy by agriculture, logging and burning, and in the western grasslands the planting of trees, coupled with cessation of burning, converted great areas into potential Indigo Bunting habitat. This species has apparently responded to these changes with a great increase in population and extension of range. . . ."
The ecological succession of forest floras in Maine during the past century has been accompanied by marked changes in the indigo bunting population at this northern limit of its breeding range. Palmer (1949) traces the species decline there, which began in the late 19th century and continued until the 1930's. As the automobile replaced the horse, large acreages of pasture were allowed to revert to forest, and the indigos started to reappear. "There has been a marked increase during the past decade, the species again being noted as a regular migrant and breeder, especially inland in southwestern Maine. . . ."
The following table indicates some of the preferred breeding
habitats of this species and the breeding population densities.
With few exceptions these habitats are all ecologically
similar--open areas with dense cover for nesting and feeding
and the availability of high singing perches.
|Reference||Breeding habitat||Population count or estimate|
|Warbach (1958)||residential area||1/acre|
|5 (nests)/7.08 acres
|Johnston (1947)||forest edge
3-9 pairs/100 acres
|Johnston and Odum (1956)||20 year-old grass-shrub field||4 pairs/100 acres|
|Odum (1950)||hemlock sere: mesic shrubland
oak-chestnut sere: xeric shrubland
|7 pairs/100 acres
18 pairs/100 acres
|Norris (1951)||old field and fence-row||0.7 pairs/100 acres|
|Stoddard (MS.)||tung oil groves||1 pair/2-3 acres|
|Johnston (MS.)||overgown area once cleared for building||11 pairs/77 acres|
|Fitch (1958)||1 pair/2.7 acres|
|Brewer (fide Fitch, 1958)||swamp thicket||1 pair/0.26 acre|
|Stewart and Robbins (1958)||apple orchard
dense second growth
field and edge habitat
dry deciduous scrub
|13 pairs/25 acres
4 pairs/21 acres
3 pairs/19.5 acres
9 pairs/66 acres
1.5 pairs/26 acres
Nesting.--The extensive breeding range through the many habitats noted above entails a correspondingly wide choice of nest sites. William Brewster (1906) points out that the species may nest "in raspberry or blackberry bushes near farmhouses; in barberry or hazel thickets about the edges of remote fields and pastures; and in young sprout growths on the borders of woodland." Trautman (1940) specifies the brushy edges in the openings of a swamp forest. The territory he studied was a buttonbush community.
C. R. Stockard (1905) describes nests in Mississippi as being not only in low bushes and blackberry vines near the edges of fields, but also in dense cane thickets, in which the foundation of the nest was made entirely of cane leaves. The nest was only a few feet from the ground. In Alabama, L. S. Golsan and E. G. Holt (1914) described the species as a common summer resident of old fields and ditch banks in Autauga and Montgomery counties. One nest was composed of grass and leaves and lined with fine grass. It was suspended three feet from the ground in the crotch of a hackberry bush on a ditch bank in an open hayfield. Another compact nest was four feet up in a clump of sweet gum bushes on the edge of a swamp and cultivated field. It was composed of cane leaves and weed stems, and was lined with fine grass and wool.
M. G. Vaiden wrote Mr. Bent of finding 14 nests within a cotton patch of three acres in Rosedale, Miss., between May 18 and May 29, 1936. Some contained eggs; others were not completed. "Practically all the birds were successful in rearing their young. The cotton was continually worked during the last of May, June, and July, and only two nests were destroyed. The nests in each instance were within 3 to 7 inches of the top of the growing stalk. If the bird had selected the branches, all nests would have been destroyed by the plowman."
O. A. Stevens in a letter to Mr. Bent describes a nest in northeastern Kansas on a stalk of Jerusalem artichoke (Helianthus tuberosus) in a cornfield. The nest was placed under one of the broad leaves. A. Lang Baily (1954) observed a nest in Colorado on Aug. 5, 1943, two feet up in a thistle (Cirsium lanceolatum). The site was marginal weed growth of a dense roadside thicket which included a heavy stand of ragweed (Ambrosia trifida) and cordgrass (Spartina sp.).
In South Carolina, E. E. Murphey (1937) considers the species a widely diffused and abundant summer resident, but absent from sandy oakflats, pineries, and dense swamps. The bird frequented hedgerows, roadside trees, swamp clearing, the edges of small watercourses, and particularly the cottonwood trees growing so abundantly along the banks of the Savannah River. Nests were in thickets, usually adjoining open fields, and sometimes in bramble patches. Preferred to all other locations were small canebrakes where the canes were no more than one-third of an inch in diameter, and not over six feet in height. The foundation and outer layers of the nest were usually made of the dead leaves of this cane, even when the nest had been constructed at some distance from the brake.
Trautman (1940) states that in the Buckeye Lake region of Ohio the species "nested wherever there was a fair amount of brush, and all brushy thickets, fields and meadows, overgrown fence rows, edges of woodlands, openings in wooded areas, and borders of dirt roads contained nesting pairs. . . . Nesting birds avoided the wetter portions of swamps, cleared fields, heavily grazed meadows, pastures, and woodlots, and the most mature forests with little shrub layer. . . ."
Maurice G. Brooks (1944), speaking of West Virginia, calls the species a "characteristic breeding bird of the oak-chestnut forest at all elevations. Much less common in the northern hardwoods, and in coniferous forests, but abundant and generally distributed in the oak-pine areas. I have not found it in the spruce forest."
R. S. Palmer (1949) says that in Maine several pairs sometimes nest in a fairly extensive area of blackberry bushes and other brush. They seem to be drawn together by habitat requirements rather than by any tendency toward colonial nesting. Richard S. Phillips (1951) mentions specifically nests in red raspberry, wild raspberry, elm seedling, elm sapling, silver maple sapling, wild rose, and ironwood sapling. Nests were situated 5 to 200 feet from the woods. T. S. Roberts (1932) states that the species occurs on prairies rather infrequently in the groves of natural timber about lakes and streams.
William Brewster (1906) describes a nest placed "in a clematis vine trained on a wire trellis which screens the main entrance to my museum. Although no one could enter or leave this building without brushing against the foliage of the vine, the birds completed their nest, but they abandoned it after laying two eggs."
Thus, nests are generally placed in crotches of shrubs or saplings only a few feet from the ground in dense cover. Phillips (1951) found the mean height above ground for 14 nests in Ohio was 31 inches. In Grady County, Ga., Herbert L. Stoddard, Sr. has found nests at the end of a tung tree branch not over 18 inches above the ground, but the more usual location in these trees is from 5 to 15 feet up. Evidently selection of the particular nest site, as well as nest construction, is left entirely to the female (Allen, 1939). Knight (1908) gives the measurements of a nest as: outside depth, 2 1/2 inches; inside depth, 2 inches; outside diameter, 3 1/4 inches; inside diameter, 2 1/2 inches. A. O. Gross (1947) mentions a nest in August at Brunswick, Maine, "held together in part by a few spider webs." He says, "The outside measurements of the nest were 3 3/4 X 4 1/2 inches and the depth 4 1/2 inches. The nesting cavity was 1 3/4 X 2 inches and a depth of 2 inches." The three young were seen in the nest on Aug. 29, 1947, and out of it the next day.
Basically, the nest is a well-woven cup containing a variety of materials--dried grasses, pieces of dead leaves, strips of bark, Spanish moss, and weed stems. Lewis McIver Terrill wrote Taber that nests in the southern part of the Province of Quebec are bulky and loosely made, and their chief feature is the "invariable use of quantities of skeletonized leaves." Bailey (1954) reports finding facial tissue and cigarette papers in a nest in Colorado. Lining materials include cotton, feathers, fine grasses, wool, rootlets, and long hairs from animals such as Angus cattle and horses. J. Suthard (1927) reports having collected "during various seasons and in different localities several nests of this species composed partially of snake skin. None of these were lined with snake skin, but all had it combined in the lower portion of the nest, or woven in the sides and brim. One nest collected July 23,1923, has the entire lower portion composed of snake skin. There are long strips of skins streaming from the bottom of the nest."
Mr. Bent's notes mention watching a female stripping cedar bark from cedar poles. He later found the nest. He also comments on the vociferous solicitude of the parents as being of assistance in locating nests, even before the young are hatched. Hazel L. Bradley's (1948) life history study mentions birch bark as nest-building material.
Trautman (1940) states:
The nests were made chiefly of small rootlets, grasses, inner bark of vines and herbaceous plants, and bits of leaves and were lined with finer grasses, hair, or feathers. The nests were placed in shrubs, bushes, or small saplings and were 1 to11 feet above the ground. Females were seen carrying nesting material as early as May 20, and by May 30 nest building was well under way. The earliest nest with eggs was found May 27 (1928, 3 eggs), the latest August 4 (1932, 3 eggs); the earliest nest with young was seen June 12 (1932, 4 young), the latest September 5 (1929, 4 young); the first fledgling out of the nest was noted June 21 (1925, 1 young), and the last September 12 (1929, 2 young). Most of the nests with eggs were found from June 16 to July 20, the majority of nests with young from July 10 to August 10, and most of the fledglings out of the nest from July 15 to August 20.
Doris Huestis Speirs wrote Taber about a nest she found in Ohio June 28, 1951, about 17 inches from the ground in a small hackberry sapling. The three eggs were side by side, parallel. When first observed the following day, they were still in this same position, but on a second visit at 9:50 a.m. some 65 minutes later, the eggs had "been rearranged in a more conventional design." When approaching the nest the female first clung to the bark of a little cedar tree rising above the bush, then went to the nest. The male came down once from a hackberry tree to the cedar, then dropped into the nest-site, but quickly departed. The young hatched July 6 and were still present on July 12. On the other hand, Lillian Cleveland (1903), who watched a nest finished on May 30, never saw the male near the nest.
Eggs.--Varying with the year and location, nests with eggs may be found from May to August. Some extreme egg dates are as follows: Maine, late June-July 15 (Knight, 1908); New York, May 25: first of August (Eaton, 1914); Michigan, May 26-August 16 (Barrows, 1912; Berger, 1951); Ohio, June 6-August 7 (Phillips, 1951); Maryland, May 24-August 16 (Stewart and Robbins, 1958); North Carolina, May 22-July 16 (Pearson, Brimley and Brimley, 1959); Georgia, May 17-July 23 (Burleigh,1958); Alabama, May 12-August 12 (Imhof, 1962). The consensus of many observers is that the species is usually double-brooded. Apparently no one has studied a marked population to prove double-broodedness, but Burleigh (1958) states: "Two broods are reared in Georgia each year, the first in late May and early June, the second in July." And Pearson, Brimley and Brimley (1959) claim that in North Carolina "two broods often are reared in a season, each, of course, in a freshly built nest." According to Parmelee (1959) "Allen says it is double-brooded and that the interval between the start of the first nest (early June) and the second (late July or early August) is long." To what extent a late nest represents renesting following an unsuccessful earlier attempt at nesting is not known.
A. A. Allen (1933) says that if the first nest is started as early as the first of June, it is the last of July or first of August before the second nest is under way. He questions whether the species customarily uses the nest a second year because of the presence of mites and the changes in the locations of the leaves that afford concealment and protection. H. C. Oberholser (1938) states that occasionally the same nest is used. E. H. Forbush (1929) goes further and says that the nest is sometimes repaired and occupied year after year.
F. M. Chapman (1932) states that the usual clutch is three to four eggs, pale bluish white, but two-egg clutches are known from Alabama (Imhof, 1962), northern Florida (Johnston), and California (Bleitz, 1958). Oliver Davie (1889) describes the color as "white, with a bluish or greenish tinge, unspotted or rarely thinly dotted with brown. . ." and Barrows (1912) found in Michigan "perhaps one nest in a hundred [with]. . .one or two eggs which have small specks of brown on the larger ends." Sometimes eggs are nearly pure white. A. D. DuBois, writing Mr. Bent about a nest in Illinois which contained four eggs on June 2, 1908, says, "The yolks in these eggs showed through the shells, neutralizing the bluish tint to such an extent that the eggs appeared quite white in the nest."
The measurements of 50 eggs average 18.7 by 13.7 millimeters; the eggs showing the four extremes measure 21.3 by 14.2, 19.1 by 15.0, 16.7 by 12.7, and 17.8 by 11.7 millimeters.
Incubation.--The incubation period is recorded by Roberts (1932), Allen (1939), and Forbush (fide Parmelee, 1959) as 12 days, and by Sprunt and Chamberlain (1949) as 12-13 days. Both Bradley (1948) and Allen (1939) agree that incubation is performed by the female alone, but Forbush claims that both sexes incubate and attend the nestlings.
Young.--Extreme nestling dates are available for a few regions: Maryland, June 5-August 30; Alabama, June 3-August 28. Alexander Wetmore (1909) mentions taking a young bird just out of the nest Sept. 18,1908, and comments on such unusually late nesting. Bradley (1948) states that 8- and 9-day old birds fledge as very weak flyers and remain at or close to the ground. Burns (1921) gives 9 days for the nestling time, Forbush (1929), 10-13 days, and Allen (1939) gives 10 days. A. L. Goodrich, Jr. (1945) says that the male "joins his mate in foraging for the clamorous youngsters until they become able to fend for themselves," and G. M. Sutton says "the male may take complete charge" while the female renests. The males, however, apparently never brood the young birds. In fact, Dr. Sutton writes: "I have never seen a male take food to, or change places with, a brooding female, and I have never flushed a male directly from the nest." Mrs. Speirs writes that in the case of nestlings she watched, the female seemed to do most, if not all, of the feeding. Spiders of one kind or another comprised the principal diet fed the young. Other foods consisted of a bee, a few mayflies, a chrysalis, a butterfly, a winged insect, a caterpillar, a daddy longlegs, and a buff-colored moth which was stuffed, wings and all, into the mouth of a fledgling. The female removed a large number of fecal sacs.
H. Dearing and M. Dearing (1946) watched young birds in Arizona, near a benchmark elevation of 4,875 feet. Commenting that the adult male bird had first been seen on July 4, the Dearings say:
The female Indigo Bunting was not seen until July 23, when the young came off the nest. The nest was not seen but the fuzzy brownish fledglings appeared that morning, and both parents were much excited about them. The male hopped excitedly about one of the fledglings on a low branch of a walnut tree near us. The female fed a second fledgling in a near-by shrub. Another was discovered low in an apple tree. We watched it sit perfectly still for more than twenty minutes, and we wondered how the parents would find it. Without a sound from parent or fledgling, the female flew straight to the latter, fed it, and flew away. The fledgling remained in its place. . . .
On July 24, we saw the parents together carrying food to three or four young in an alder tree near the road. The next day the family was still in the alders. The male, with a green caterpillar in his beak, flew from the orchard and fed a young bird. We saw the male again on August 1 and nearly every day after that until August 8.
Hazel L. Bradley's study (1948) indicates that newly hatched birds are pinkish orange in color, almost bare, but with bits of gray natal down on some of the feather tracts. There are large bulges for the eyes, which are closed and membrane-covered at first. One bird opened its eyes at the age of four days; all had the eyes opened at five days. The large wing feathers seemed to be emerging from their sheaths at five days of age, and pin feathers also appeared along other feather tracts, particularly on the back. At six days feathers were out of the sheaths and enlarging. At 11 days of age one group of young was capable of flights of 20 feet or more. The female had removed egg shells, brooded the young, fed them, and eaten or carried away fecal sacs. Nest defense was the one activity in which the male participated.
Commenting on helpers among birds, Alexander F. Skutch (1961) notes for indigo buntings that "juveniles fed still younger birds in captivity." And Val Nolan, Jr. (1961) found that "Prairie Warblers accept and feed nestling Indigo Buntings" and that the buntings will accept young prairie warblers.
Few data are available for productivity. In Michigan, Berger (1951) notes: "From eight eggs in four non-parasitized nests, six buntings were fledged. Five parasitized nests containing seven host and ten Cowbird eggs fledged two buntings and four Cowbirds." Phillips (1951) found that 18 young fledged out of 41 eggs laid.
Cowbird Parasitism.--As suggested above, a serious factor in the breeding success of indigo buntings is nest parasitism by the brown-headed cowbird (Molothrus ater). Berger's study (1951) in Michigan revealed the fact that five out of nine bunting nests were parasitized; three contained one cowbird egg, one contained two, and one contained four eggs. In these nests four of the cowbird eggs hatched and all four young cowbirds were successfully reared. In Ohio, Phillips (1951) found that 6 out of 14 nests were parasitized and one cowbird fledged from seven eggs laid. Howard Young (1963) gave the following summary for cowbird parasitism on the indigo bunting: 12 out of 26 nests were parasitized; 6 out of 17 cowbird eggs hatched and all 6 fledged. The first recorded breeding of the indigo bunting in California was in Los Angeles County where Don Bleitz (1958) found a nest containing one cowbird and two bunting eggs. Rarely, as Friedmann (1929) reports, a cowbird will lay her egg in the nest of a bunting already containing young.
Trautman (1940) graphically presents the susceptibility of this species to visitations from the cowbird. He states that out of 16 nests examined, 5 contained three eggs or young each of the indigo bunting; 3 contained three eggs or young of this species and a cowbird egg or young each; 6 contained four eggs or young each of the indigo bunting; and 2 contained four eggs or young of this species and a cowbird egg or young each. On more than 10 occasions Trautman observed indigo buntings feeding cowbird fledglings out of the nest.
T. S. Roberts (1943), under a discussion of the cowbird, states that the indigo bunting may "bury the Cowbird egg or eggs by building a new floor in the nest." He also gives an interesting account of the female's reaction to a cowbird's egg, saying: "Attention was directed to an Indigo Bunting's nest by the constant chipping and great agitation of the female, in which the male joined to a lesser extent. The female went repeatedly to the nest, which was low down in a gooseberry bush, and, after looking in, returned each time to the lower limbs of an overhanging tree, displaying the greatest alarm and distress. Examination showed that the nest contained two eggs of the owner and a Cowbird's egg. It was suspected that the Cowbird's egg had just been deposited and was causing the disturbance. It was removed, and after the next visit and inspection by the worried little bird, the fussing and excitement subsided at once."
A. D. DuBois wrote Mr. Bent of finding a nest that contained two cowbird eggs, but no eggs of the indigo bunting. He adds, "No eggs of 'indigo' had been added when revisited 5 days later." W. T. Allen (1881) mentions a case where "The cowbird had apparently deposited an egg in their nest before it was quite finished, whereupon the owner built a new bottom so as to leave the obtruded egg enclosed between the two and proceeded to lay its own eggs on top."
Plumages and Molts.--The definitive work on this subject was published by Dwight in 1900. Chapman's brief discussion (1911) generally agrees with Dwight's descriptions. Contrary to the usual situation in male fringillids, the male indigo has at least five recognizable plumages. The brownish mouse-gray natal down is replaced through a complete postnatal molt by the juvenal plumage. This plumage is characterized by being dark brown above, and by having a pale clove-brown tail faintly edged with greenish or glaucous blue. Under parts are dull white, narrowly streaked with sepia on the breast and sides. The bill and feet are pinkish buff; with age the former becomes dusky and the latter black.
A partial post-juvenal molt, usually commencing in August, involves body feathers, wing coverts, sometimes the tail, and sometimes five or six outer primaries. The resulting first winter plumage resembles the juvenal plumage except that the bird is not so brown above and the streaking of the under parts is less distinct. Generally brownish in this plumage, the lesser wing coverts, upper tail coverts, rump, and rectrices are often faintly washed with a bluish tinge. Dwight examined a few specimens taken as late as October 2 in which a postjuvenal molt of remiges and rectrices was not yet completed. He ascribes the occasional post-juvenal renewal of tail and primaries to 'individual precocity of southern-bred birds."
The first nuptial plumage, acquired by a partial prenuptial molt in February and March, involves some body feathers, the tail, five or six outer primaries (sometimes all of them, but usually not their coverts), most secondary coverts, tertiaries, and a variable number of secondaries. Thus, some individuals may undergo a complete prenuptial molt at this age. "This moult produces a variety of birds, all with brown primary coverts, some specimens being as bright blue as are adults. . . . A mixture of blue and brown results. The most surprising renewal is that of the distal primaries without their primary coverts. . . . a new black tail edged with blue is assumed unless it has already been acquired at the post-juvenal moult. . . . The bill becomes slaty. . . . It is natural to assume that birds which acquired new wings and tail in the autumn are the worn duller specimens we find in May, while the brighter less worn birds are those which have acquired these feathers at a more recent date." In this first nuptial plumage one can usually also see varying amounts of white on the abdomen. Birds in this plumage are known to establish territories and probably breed.
The adult winter plumage is acquired by a complete postnuptial molt occurring in August or even September. It is "strikingly different from first winter dress in the depth and richness of the brown and the marked blueness of the wings and tail. . . . The wings and tail are black, edged with blue. . .the primary coverts are black, edged with blue which is apparently pale in the less precocious birds and deeper in those more vigorous."
The adult nuptial plumage is usually acquired by an incomplete molt in the spring, but there is evidence from captive birds that this molt is sometimes a complete one (Johnston). In any event, most of the body feathers, some wing coverts, and tertiaries are replaced. "The blue of the head is always deeper than elsewhere, and the feathers of the lores and interramal space are black." Chapman (1911) states unequivocally that the rectrices are not included in this molt. There is no evidence to support the erroneous earlier belief that the adult male indigo plumage is acquired by wear of winter feathers without molt. Adult males undergoing this prenuptial molt have been collected between December and May.
The duration of the adult's postnuptial molt, though a complete one, is incompletely understood because some individuals migrating southward from the United States have completed the molt whereas others observed in late autumn in Jamaica and Guatemala were still molting.
Dwight suggests that "the plumages and moults of the female correspond to those of the male, the prenuptial moult, especially the first, apparently limited or sometimes suppressed." In both the juvenal and first winter plumages, females closely resemble males but have little or no bluish tint on the lesser secondary coverts and tail. "In first nuptial plumage (which is in many cases apparently the result of wear) a greenish tail and few greenish edged primaries are assumed together with a few whitish feathers below." The adult winter plumage is similar to the first winter plumage but the underparts are less obviously streaked. We question Dwight's assertion that "the adult nuptial [female] plumage is attained chiefly by wear."
Alexander Skutch wrote Mr. Bent as follows: "When they arrive in Central America in the fall, the male indigo buntings display at most scattered flecks of blue on their modest brown plumage. Gradually during the winter months they acquire the indigo-colored nuptial dress. As early as January 5 I have seen a male predominantly blue, but still flecked with brown. During February many lose all the brown contour feathers and seem to be in full breeding plumage. But other individuals, probably young males, are still merely speckled with blue when the northward movement begins in the latter part of March; and some are still noticeably flecked with brown as late as the end of April."
Again referring to Guatemala birds, Ned Dearborn (1907) points out that "By the middle of March adult males had about half of the head and breast blue, the back and underparts being still in fall plumage. Males taken in January had a few scattered blue feathers both above and below. . . . Iris dark brown."
G. M. Sutton (1935), studying Michigan birds, gives evidence suggesting that the young start molting into the juvenal plumage when about 16 days old and then undergo a postjuvenal molt in midsummer.
Food.--This wide-ranging species has adapted itself to a diversified diet. W. L. McAtee (1926) says, "Professor S. A. Forbes collected 18 specimens in an Illinois orchard infested by cankerworms and found that all but one of the birds had fed on the worms, which formed 59% of the total food of the birds. He found in these stomachs, also, remains of other caterpillars, leaf chafers, weevils, click beetles, and bugs." McAtee also lists as food one of the locust borers (Agrilus egenus), grasshoppers, plant lice, and cicadas. He says, further, that "the bird feeds to some extent also upon grain, as oats, and upon buds, but seems rarely to do notable damage." In another report W. E. Clyde Todd (1940) states: "According to E. H. Forbush, it consumes large quantities of objectionable insects, such as grasshoppers, caterpillars, measuring worms, and beetles; it also eats seeds, many of which are those of weeds. Examination of stomach contents of a few birds collected in an orchard infested with cankerworms, revealed that 78 percent of the total food consisted of this pest." In Alabama (Imhof, 1962) and North Carolina (Pearson, Brimley and Brimley, 1959) the species consumes a variety of weed seeds, berries, other fruits, caterpillars, grasshoppers, beetles, and bugs.
A. W. Butler (1898), commenting on the abundance of the species and its occurrence around farms and even small fruit gardens, says, "it is desirable that they receive the fullest protection, for at any time they may prove of untold value in assisting to hold in check some threated outbreak of injurious insects." As other foods he also mentions raspberries and elderberries.
T. S. Roberts (1932) lists plant lice, flies, and mosquitoes as food, and H. C. Oberholser (1938) records curculios. O. W. Knight (1908) includes vegetable matter such as seeds of the goldenrod, aster, thistle, and other composites, as well as grass and weed seeds. E. H. Forbush (1929) says, "In late summer when the corn has 'tasseled out,' the Indigo Buntings seem to find some food about the corn tops and often may be found in cornfields." Witmer Stone (1937) observed a bird eating dandelion seeds on a lawn in early May. Mabel Osgood Wright (1907) says, "The last of May, one of these Buntings came to a low bush, outside my window, and after resting awhile, for the night before had been stormy, dropped to the closely cut turf to feed upon the crumbs left where the hounds had been munching their biscuits."
E. W. Jameson, Jr. (1942) watched migrating flocks from Aug. 20 until Sept. 22, 1942 along the sand dunes and rocky shores of northeast Lake Erie where turkey bluejoint (Andropogon furcatus) grows abundantly. He says, "The birds perched just below the racemes on the two-meter culms, bending them half way to the ground, and then ate the grains on that culm or on an adjacent shorter one. The grains had not yet fallen at this time, and I did not see the buntings feeding on the ground or using any other plant for food. At 9 a.m. on September 17, seventeen buntings were feeding in this manner within an area of about one acre; some were perched in nearby willows in company with Song Sparrows and Chipping Sparrows. However, I did not see these sparrows feeding on bluejoint. When I left Pint Abino on September 22, buntings were present in about the same numbers as during the previous few weeks, and bluejoint still formed the major part of their diet."
Frederick V. Hebard wrote Mr. Bent that on Oct. 12, 1945, he saw at least a hundred of these birds in southern Georgia feeding in a field well studded with crotolaria, and that about a year later, Oct. 16, 1946, a vastly larger number was there.
In southwest Georgia, Herbert L. Stoddard, Sr. noted that "the abundance of insect life in the vetches and Crimson Clover, coupled with the mixed small grains grown for the game, provides an abundance of preferred food for the breeding Indigos and their young."
Other foods are mentioned under the section entitled Winter.
Behavior.--Among the conspicuous behavioral traits of male indigos is their strong territorial defense. This is manifest, first of all, by their persistent singing from tall perches as noted under Voice. Todd (1940) states that the male "seeks some prominent perch, such as an electric wire or a high branch of a dead tree--often the topmost one. . . ." Then, too, males pursue intruding males with verve as noted by Van Hoose (1955). In this instance a male, probably breeding at San Marcos, Coahuila, Mexico, was seen chasing another male on May 5, 1954; the female followed the first of these males. Furthermore, territorial male indigos have been seen defending their territories by song and pursuit against male lazuli buntings (Wells, 1958). Thus, the species is characterized by having inter- and intraspecific territorial defense.
W. E. C. Todd (1940), while driving through a woodland, "saw a pair of indigo buntings in the middle of the road a short distance ahead, the male spreading his wings and dancing about the female. They paid no attention to the car, and, as we were too close to do more than slow down, the car passed right over them. When we looked back they were still in the same place and unhurt."
Hervey Brackbill wrote Mr. Bent as follows: "Once a male behaved protectively toward a very young fledgling that I had picked up just as it was about to be fed a caterpillar. While I was holding the young bird, the parent flew about wildly within as little as 3 feet of me, uttering a variety of notes--chip, tit, and quit were among them--sometimes in long strings. Then, after I had put the fledgling back on the ground, the male clearly tried to draw it away from me by flying close to it and then off in one direction or another. Finally its offspring did flutter after it into some undergrowth."
Witmer Stone (1937) mentions "a brilliant male found bathing in a rain water pool in the pine grove at the Point on July 2, 1930. . . ."
T. D. Burleigh (1941) records an interesting observation in western North Carolina. He says: "Appearing with unfailing regularityin the fir and spruce woods (6,500 feet) in early July, this species is unique in that throughout the month only adult males are seen, singing each day from the upper branches of the larger trees. At no time have females or young of the year been noted above an altitude of 5,000 feet. Extreme dates for the occurrence of these wandering males at the top of the mountain are July 5 (1931) and July 31 (1934)."
Females, on the other hand, stay secretively low in the brush and usually can be seen only by the exertion of determined effort. W. Leon Dawson (1903) says, "she is a most prosaic creature, skulking about through thickets and briar patches or fussing with the children. . .the soul of suspicion, and her protests are so emphatic that the inquisitor believes himself 'hot' when he may be a dozen yards away." F. M. Bailey (in Chapman, 1932) mentions the female twitching her tail nervously from side to side. Males do this also. In contrast, Bailey describes a male which, "day after day, used to fly to the lowest limb of a high tree and sing his way up from branch to branch, bursting into jubilant song when he reached the topmost bough."
Thomas Nuttall (1832) says, "They appear to show great timidity about their nest, and often readily forsake it when touched, or when an egg is abstracted. . . . They will not forsake their young however ready they may be to relinquish their eggs; and they have been known to feed their brood very faithful through the bars of a cage in which they were confined."
W. and E. Shackleton (1947) describe "anting" by three wild indigo buntings on four consecutive days. This is of special interest in connection with the failure of the painted bunting under study to "ant" (L. M. Whitaker, 1957).
Voice.--The indigo bunting is one of those species in which, according to Borror (1961), different individuals have songs of many different patterns with little or no overlapping between birds. In fact, he suggests: "Our recordings do not contain any instance of two different birds singing songs of the same pattern. . . ." Nonetheless, in the words of Winsor M. Tyler, "this song has a character shared by no other. There is a whole-souled concentration about it. The bird, when he sings, sings just as well as he can, and I believe just as loud as he can--he gives himself up entirely to singing and throws the notes out for all he is worth. . . . [The song] often suggests a goldfinch, but a point of difference is that in the song of the indigo bird nearly every note is accented, giving it a definite character, and the per-chic-o-ree phrase, so common in the goldfinch's voice, is not introduced. A bright, far-carrying song, suggesting happiness, even exuberance."
J. H. Langille (1884) calls the song "A sort of hurried warble, quite fluent, and yet seeming to stick in the throat a little. . . . Its tones are musical, being loud at first, but growing faint at the last, as if the singer were exhausting his lungs. . . ." This latter point is well taken.
Ralph Hoffmann (1923) considered the song as resembling the syllables, "swee-swee-swee, swee-swee (slightly lower), sweet-sweet-sweet, swee-swee (slightly lower), swee, swee, swee." Arthur A. Allen (1933) affords another interpretation, "Sweet, sweet-where, where-here, here--see it, see it."
Nuttall (1832) describes a shorter song "usually uttered at the time that the female is engaged in the cares of incubation, or as the brood already appear, and when too great a display of music might endanger the retiring security of his family. From a young or imperfectly moulted male, on the summit of a weeping willow, I heard the following singularly lively syllables, tle tle tle ta lee, repeated at short intervals."
Aretas A. Saunders writes as follows: "The song of the indigo bunting consists of a short series of high-pitched notes delivered with a sibilant, wiry, and somewhat strident quality. The notes are grouped together, both by rhythm and pitch, in pairs, with occasional single notes taking the place of a pair, or more rarely three or four shorter notes occupying the same amount of time as a pair, or a single note. Each pair or group of notes is the same pitch throughout, but nearly always a different pitch from that of the pairs immediately succeeding or preceding it. An occasional slurred note, or group of two slurs occurs."
Saunders emphasizes the high-pitched rather brassy quality, with harsh z-like consonant sounds. The chief character, with which we agree, is the rhythm. Notes vary from 6 to 21, averaging about 11. Songs vary in length from 1 1/2 to 6 4/5 seconds, averaging about 2 4/5. Pitch ranges between F6 and D#7. The pitch interval varies from 1 1/2 to 5 tones, but over half his 49 records are just 2 1/2 tones. In a letter to Mr. Bent he says, "One remarkable song that can give an idea of the rhythm, was zay-zay zreet zay-zay zeah zay-zay seeteeteet zit-zit zeah. The remarkable thing about this is that the rhythm is exactly that of a well-known human jingle, 'Bean porridge hot, bean porridge cold. Bean porridge in the pot, nine days old.' Occasional songs have one or two notes standing out as louder than the rest of the song, but there is nothing definite or regular about the position of these loud notes."
He comments that songs are short during May and June and possibly the first half of July. The short songs vary from 6 to 13 notes, averaging 9 1/2. In July normal songs are 14 notes, but sometimes prolonged to 19. "The season of song lasts from the bird's arrival in spring to about the middle of August, or somewhat later than this in certain years."
The pitch, or number of vibrations per second, as studied on one bird by Albert R. Brand (1938) ranged between 8875 and 3250. The approximate mean was 5700.
Mrs. Speirs writes that at South Bass Island, Ohio, on July 11, 1951, an indigo bunting commenced singing at 4:43 a.m. and sang 15 songs a minute for four consecutive minutes, plus one incomplete song. She counted 240 songs in 34 minutes including the foregoing. The bird sang throughout the entire day to a greater or less extent until 7:38 p.m.
T. S. Roberts (1932) watched a male that sang the "livelong day" with exact regularity from the top of a flagpole. The "song was just four seconds in length with intervals of six seconds. During June and July he began singing very regularly at 4:00 a.m. and continued with surprisingly little interruption until 8:00 p.m.--about the time the Whip-poor-will began calling. Allowing four hours for rest and feeding, there remained twelve hours for singing, which, at the rate of six songs a minute, gave 4,320 songs a day, and for the two months, disregarding late May and early August, 263,520 times that he tuned his little pipe in the sixty-one days!" He describes the usual song as "sweet-toned but rather characterless. . .delivered in a lazy, indolent fashion. It has more snap early in the season, but, as the summer progresses, it becomes more and more colorless and uninteresting." Again, he says, "Occasionally the male indulges in a flight song, in which the notes are more rapid and gushing."
W. E. C. Todd (1940) states that the bird "is not at its best on arrival; but the longer it stays, the longer its song grows, and the hotter the weather, the oftener it sings. From a few bars in May and June, the song develops during July and August into a lengthy refrain with many variations." He considers the song "not particularly melodious."
Numerous observers (Chapman, 1932; Todd, 1940; Fitch, 1958) make special mention of the fact that characteristically indigo buntings continue to sing into August after most other birds have stopped. Indeed, some individuals continue to sing sporadically into September. Quantitative data of Leopold and Eynon (1961) indicate that as the breeding season progresses, the daily song period becomes markedly shortened. The light intensity values in foot-candles for the first daybreak song change from 0.014 in May to 0.022 in June to 0.74 in July. Mean light intensities in foot-candles for the evening song change from 0.51 in May to 1.00 in June to 8.92 in July.
Charles Vaurie (1946) kept records of an individual for 47 consecutive days, July 20 to September 4, 1944, on the lower slopes of a 1,000 foot hill in the foothills of the Blue Mountains in Berks County, Pa. The bird was in continuous full song with only normal intervals until August 3, then sang noticeably but with fairly long pauses until August 20. The bird ceased singing during a 6-day cold spell, then continued singing on a much reduced scale. On September 4 one particular bird out of more than two dozen was singing as at the start, in continuous full song. Vaurie considers that it "is sometimes tiresome to hear this bird sing because it can go on for hours without stopping, while the song grows harsher and harsher and begins to slur and break."
Val Nolan, Jr. (1958) watched a female near Bloomington, Ind. "This female, a bird with no blue visible in her plumage, sang during two brief intervals on May 29, 1956, a cloudy day with temperatures of 66o and 76o at the times of singing. At 0501 central standard time she mounted to the top of a 15-foot Virginia pine, the highest perch within 20 yards in scrubby old-field growth. During the next 2 or 3 minutes she sang 10 loud songs, described below, then moved a few yards and sang 10 more from a spot out of my sight. Between 0911 and 0921 she sang six times from the same general location, but again I could not see her. There was no repetition of the song during the rest of the day. . .nor did I hear the song here on four other dawn-to-dark watches and many briefer ones between May 17 and June 8.
"The songs, which were wholly unmusical, consisted of five similar windy, vibrant notes uttered in staccato fashion and seeming to my inadequate ear to rise in pitch from first to last. I was reminded of the abrupt, choppy song of the dickcissel and could not have identified the singer's species by her voice.
"A male indigo bunting was on territory in the field, and though he sang and was in view repeatedly throughout May 29, I neither saw nor heard him while the female was singing. A female was found incubating on this territory some 2 weeks later."
In spite of this detailed account it seems possible to us that Nolan's "female" was in fact a male. The individual was not taken, and it could have been a brown first-year male or an older bird that had not molted fully.
G. M. Sutton states that the flight song may last eight seconds or more and is given principally during the morning and evening twilights, although occasionally in full daylight. It possesses a gushing effervescent quality reminiscent of the flight song of the goldfinch. The bird gives the song from an altitude of 75 to 100 feet, fans the air rather laboriously or stiffly, and propels the body rather slowly in a straight line. Donald J. Nicholson wrote Taber about a bird he watched July 3, 1953, at an altitude of about 5,000 feet in the Great Smoky Mountains in North Carolina. "Flying from the top of a 140-foot-high balsam, the bird rose some 30 feet in a huge arc, then sank slowly down to the top of another balsam perhaps 700 feet distant. During the flight's 25 to 30 seconds duration the bird poured forth in midair a most pleasing but puzzling continuous babble of music.
Alexander Wetmore (1909) mentions hearing the flight song "on several occasions" in September 1908 in Kansas. According to Howell, Laskey and Tanner (1954), "In May, Mrs. Hickey heard the full song of" an indigo bunting flying overhead at night. William Youngworth (1953) considers that there are two flight songs. The first is similar to the song when perched; the second suggests that of a goldfinch.
In regions where this species is a summer resident it is, perhaps, difficult to distinguish whether a singing bird is establishing a territory, or is merely migrating through. Frederick V. Hebard wrote Mr. Bent from southeastern Georgia where the species does not breed that the birds "do not sing either in spring or fall migration as far as I can tell."
The alarm note is, according to E. H. Forbush (1929), "a sharp chip, resembling the sound made by striking two pebbles together, also a chuck." W. M. Taylor informs us that he has noted a similarity between the call note of this bird and that of the myrtle warbler. Aretas Saunders writes the "call-note of this bird is a short tsick resembling call-notes of warblers. A young bird, just out of the nest and giving the hunger call, uttered a short psink pitched on 'G'."
The distinctive call note will frequently reveal the presence of a bird in dense fields especially during migration. Call notes are often heard at night in the fall as they migrate overhead (Lowery, 1955).
Enemies.--Richard S. Phillips (1951) says, "On July 3, 1950, I saw a House Wren (Troglodytes aedon) fly from nest No. 11. When I got to the nest, I found the contents of the one bunting egg beginning to seep from a bill hole in the shell."
Arthur A. Allen (1933) refers to "mites." Mrs. Harold R. Peaseley wrote Mr. Bent of a lazuli bunting which drove away an indigo bunting. W. E. C. Todd (1940) states that the species "is frequently killed. . .by cars on the roads." Dale A. Zimmerman (1954) mentions four birds found dead on highways. F. M. Bennett (1909) describes, as elaborated on under Migration, the effects of a thunderstorm off the Florida Keys. Thomas Barbour (1923) says that in Cuba, "A very considerable number are often on sale in the bird stores, and they are great favorites as cage-birds and apparently thrive."
William Brewster (1906) includes the indigo bunting among the species "whose local decrease is probably due chiefly to persecution by the House Sparrows." Some birds, he says, ceased breeding "within ten years from the first appearance of the House Sparrows. The Indigo-birds and Least Flycatchers disappeared more slowly, but in the end almost as completely." An additional factor of importance evidently unassessed by Brewster was the change in habitat and flora resulting from the industrial and residential growth of the region. In any event, with the house sparrow becoming more and more restricted at the present time to closely built-up sections, in New England at least, the importance of that species as an enemy appears to be comparatively small.
The proximity of the nest of this species to the ground suggests that it may be especially vulnerable to snakes and other wandering marauders. In fact, H. Lewis Batts, Jr. (1958), gives this vivid account: "On June 18, 1949, a cat pounced upon a nest containing three young Indigo Buntings and one pipped Cowbird egg, ate one young, and carried away the others. . . ."
It is somewhat difficult to assess completely the effects of weather on this species, but Johnston and Bill Colson found two nests in north central Florida, each containing two cold wet eggs, probably the result of recent heavy rains. Additional mortality factors are suggested by Phillips (1951): young killed by direct sunlight on the nest and nest abandonment after having been found by humans. Tall TV towers in recent years have accounted for deaths of many migrating birds. For example, at a tower in Leon County, Fla., between 1955 and 1961, Stoddard (1962) counted 345 indigo buntings killed, most of these in the autumn. TV towers, tall buildings, and airport ceilometers throughout the eastern United States caused the deaths of 450 indigo buntings between October 5 - 8, 1954 (Johnston and Haines, 1957).
Field marks.--The indigo bunting approximates the chipping sparrow in size, being noticeably smaller than both song and house sparrows. The adult male in breeding plumage is the only small North American finch that appears blue all over. It could be confused with the male blue grosbeak, but the latter is a much larger bird, has brown wing-bars, and a noticeably heavier bill. Under certain light conditions, indigos may appear to be black or blue-green. Males in their first nuptial plumage may not be entirely blue; they may retain varying amounts of brown body feathers among the bluish ones and have white abdomens. The adult female, in the language of R. T. Peterson (1947), is "the only small brown Finch devoid of obvious stripings, wingbars, or other distinctive marks." Emphasis should be placed upon the word "obvious" because females are frequently finely streaked. In the fall and winter adult males are somewhat brownish but show varying amounts of blue on the body, wings, or tail. Fall immatures of both sexes closely resemble adult females, except that they are more streaked below. Immatures, like adult females, may be confused with female or immature painted buntings, but under good light conditions the latter species is obviously pale yellow-green, not brownish. Especially where their ranges overlap, female indigos could be quite difficult to distinguish from female lazuli buntings, though the latter have whitish wing-bars.
Migration.--Average dates and earliest dates of spring arrival are mentioned by Cooke (1911) for 93 localties. Migrants are, apparently, frequently carried north by major storms far in advance of their normal migration dates. Thus, Taber saw one on his lawn in Ipswich, Mass., on Apr. 19, 1954. Earle R. Greene (1946) considers the species an uncommon spring migrant along the Florida Keys; he records only seven birds. F. M. Bennett (1909), however, states that during the night of Apr. 14, 1909, "the region of the Florida Keys was the scene of a violent thunderstorm of several hours' duration, with lightning, heavy rain and high winds, blowing in squalls from the southwest. The morning brought fine weather. . ." Key West was full of land birds of several species. This species was present in vast numbers. On April 20 the indigo bunting ranked second in numbers on Loggerhead Key on the Dry Tortugas. There were still hundreds of males present, but only three females. None of the birds sang. At least two dozen had lost all their tail feathers and could fly only short distances like young birds.
Speaking of the Gulf Coast region of Mississippi, T. D. Burleigh (1944) says, "Numerous small flocks are seen in the spring and in the fall both on the mainland and on the islands. . . . Although single birds are observed from time to time, these buntings are most often seen in flocks numbering from five to twelve individuals."
In southwest Georgia, Herbert L. Stoddard, Sr. reports that "they appear in full plumage and song early in April (Sherwood, April 6, 1937, April 8, 1947, April 9, 1943, April 11, 1948, April 13, 1944, April 16, 1934, and 1936) and become abundant by the latter part of the month. Like the Blue Grosbeak, they first flock in the vicinity of ripening small grains, especially oats, which are widely grown in the region." Farther north, in Ohio, Trautman (1940) states that at the peak of the spring migration "30 to 90 birds could be seen daily, and it was obvious that there were several hundred present." The peak of migration generally began on May 18 and continued until approximately May 28.
In spite of the arguments by some investigators, it now appears that migrant birds utilize trans-Gulf and circum-Gulf routes to and from the United States. As early as1911 Cooke suspected different spring migration routes by stating "that the early migrants do not reach Louisiana by a land journey, from either the east or the west, but by a direct flight across the Gulf of Mexico." There is at least one record (Bullis, 1954) of indigo buntings seen migrating over the Gulf of Mexico, Apr. 18, 1952, and the abundant spring records from Mexico strongly indicate some northward migration around the Gulf. Stevenson (1957), in his study, "The relative magnitude of the trans-Gulf and circum-Gulf spring migrations," believes that most of the indigos use the trans-Gulf route. A trenchant examination of spring migration in a single season by Bagg (1955) indicates that birds made a through flight from Yucatan to Maine in 36 hours. He says: "When one considers all aspects of the situation, particularly including the April 17 Florida evidence of heavy trans-Gulf migration of Indigo Buntings, one is led toward the conclusion that the April 17 - 18, 1954, buntings in the northeastern coastal areas were trans-Gulf migrants which flew nonstop in the strong maritime tropical airflow." As yet undiscovered is the northward route taken by birds wintering in Jamaica and other portions of the eastern Caribbean area, but it is probably via peninsular Florida.
Fall migration commences in late August and may continue through early November. As compared with spring migration, fall migration entails more flocking and larger flocks. At Gainesville, Fla., in the autumn of 1963, indigos (and a few painted buntings) were attracted to a small but dense field of Johnson grass, indigo, sorghum, and beggar's lice. Between October 18 and November 8, 72 indigos were netted and banded. They all appeared to be birds of the year, and males out-numbered females about 3 to 1. During this time there were only four repeats, indicating a rapid turn-over of buntings utilizing this field. For the Mobile Bay area of Alabama, Imhof (1962) records a maximum daily spring count of 130 indigos, but a maximum fall count of 300.
Trautman (1940) says: "The southward migration began early for a sparrow and was in progress while some resident birds still had young in the nest or were in family groups. Transient flocks were observed flying overhead during early mornings of late August, and by early September migration had become pronounced. The peak took place between September 10 and 27, and then the species was as numerous as it was in spring, but was less conspicuous. In late summer the males were quiet, and both adults and young were rather secretive. . . . In this southward movement the species was found in the same brushy cover which it inhabited in spring and summer and was likewise found wherever herbaceous plants grew tall and abundant and the weed seed crop was large."
Lynds Jones (1910), speaking of the Cedar Point region in Ohio, says, "This is one of the species which helps form the great wave of migration in spring. I have not noticed any distinct fall movement of birds from farther north." However, E. W. Jameson, Jr. (1942) says that along the northeast shore of Lake Erie flocks of from 5 to 18 or 20 adult and immature birds were seen daily from Aug. 20 until Sept. 22, 1942.
Herbert L. Stoddard, Sr. writing about southwest Georgia states: "After the breeding season is over and the young birds are 'on their own,' the 'Indigos' linger with us in numbers throughout October. At this season they are flocking with other finches, largely in the vicinity of 'dove fields' of Shallu, or around the occasional sorghum patch in the farming sections."
R. W. William, Jr. (1906) says that during the latter part of August he found the species "very abundant in the sweet gums and oaks scattered here and there" in Leon County, Fla. The birds were extremely wary and remained in the topmost branches of the largest trees.
J. J. Audubon (1841) says that, "Towards fall, the young congregate into loose flocks or parties of eight or ten individuals, and proceed southward. . . . They are fond of basking and rolling themselves in the roads, from which they gather small particles of sand or gravel."
Eugene P. Odum (1960) and his coworkers (Odum, Connell, and Stoddard, 1961) have made interesting studies of the migrating birds killed at a TV tower in northern Florida. Between September 23 and October 9, 55 indigos were obtained; these dead birds were ground up and their body fats extracted chemically. Total fat averaged about 2 grams per bird (13.45 percent of body weight). From these and other data, these investigators estimated flight distances from 100 to 1,820 kilometers. They concluded: "According to our estimates only about six individuals out of a sample of 55 birds extracted would have been able to continue across the Gulf. Most of the individuals would have had to follow the coast or stop for extensive refueling, since the average fat index for the whole group was only about 13 percent." It now appears from the unpublished work of Johnston that a significant portion of the population migrates southward through peninsular Florida.
Winter.--Indigos spend the winter rarely in the southeastern United States but more commonly in south Florida. There are occasional winter records for the District of Columbia (Stewart and Robbins, 1958), North Carolina (Pearson, Brimley, and Brimley, 1959), Alabama (Imhof, 1962), Mississippi (Burleigh, 1944), Louisiana (Lowery, 1955), and northern Florida (Sprunt, 1954). For the West Indies, Bond (1961) mentions specifically winter records between October 10 and May 8 on the Bahama Islands, Cuba, Isle of Pines, Swan Island, Jamaica, and Puerto Rico. He suggests, however, that the species winters "chiefly in Central America." On Cuba it is regarded as "another bird of spring and autumn passage" (Barbour, 1923). On several occasions indigos have been noted in California in winter (Williams, 1961; Wilbur, 1963).
The bulk of the indigo population appears to winter "from Jalisco [Mexico], Guanajuato, San Luis Potosi to central Panama, casually to Venezuela" (Friedmann, Griscom, and Moore, 1957). The southernmost record for the species appears to be in Columbia where de Schauensee (1964) states that it is casual, being recorded in northern Choco and Magdalena in January and February.
For the Monserrate area of Chiapas, Mexico, Edwards and Lea (1955) state: "In the mesquite-grown fields we often encountered flocks of this species near, or mixed with, small flocks of Guiraca caerulea, from March 26 to April 1." Loetscher (1955) describes indigos in Veracruz as being of regular but local and uncommon occurrence during the winter along the coastal plain. From sea level up to about 4,000 feet it is locally common during migration.
Accounts of the species in Guatemala are many. In that country it is common in small flocks especially in brushy meadows, open country, forest edge, and second growth. Tashian (1953) notes that indigos were "especially abundant at Bellavista where they were usually observed in large mixed flocks of which Lesser Goldflnches formed the nucleus." Baepler (1962) took specimens at 7,600 feet elevation in scrub oak and in an oak thicket at 6,900 feet. Land (1962, 1963) records them up to 6,000 feet, and states that "three specimens taken in late November were molting. Males taken up to February 15 were at least partly in winter plumage." Ned Dearborn (1907) states that Guatemalan birds were very common all winter, at least up to 4,000 feet. He says that "At Finca Chapulco, near Los Amates, these birds were daily feeding on the ground in the door yard. Often they were found in company with Sporophila among the weeds that flourish along the railroad."
J. Van Tyne (1932) mentions this species as wintering at Uaxactun in 1931 "in large flocks in the open grassy clearing. Flocks of scores were constantly to be seen feeding on grass seed. They came especially to the mule corral to pick up waste grain. . . . He banded 99 birds and recorded 120 repeats in about a month. The birds were quite tame and banding operations indicated that they were "extremely sedentary," even though the "species was common all over the clearing of hundreds of acres. On the morning of April 27th the species. . .had disappeared. A circuit of the clearing revealed no Indigo Buntings. I thought they had left for the North, but on the 28th I saw again small flocks and noted bands on the legs of some birds. However, they were very restive, wandering about and not coming to the trap. On April 30th one was retaken in the trap and other banded birds were seen. The main flock probably left for the North that night, for we saw none thereafter, though two unbanded females were taken later (May 4th and 13th) in nets in the forest." He lists birds of both sexes banded in 1931 and retrapped there in 1932.
D. R. Dickey and A. J. van Rossem (1938) describe the bird in El Salvador as a "common fall and spring migrant and winter visitant to grasslands and fields throughout the Arid Lower and Arid Upper Tropical zones. The extreme dates of arrival and departure were October 26 and April 30." They say, "good-sized flocks were found in suitable territory everywhere below 3,500 feet. Although the species was less numerous in midwinter than during migrations, still it was fairly common in grasslands, fields and pastures, and at times even invaded the more open second-growth woodland. . .a few even penetrated the coffee groves, an environment in which they seemed strangely out of place."
Alexander F. Skutch wrote Mr. Bent as follows: "The indigo bunting arrives in Central America during the latter half of October and soon spreads over the whole length of the region, as far south as western Panama. Although on October 20, 1933, I met a migrating bunting as high as 8,500 feet in the Guatemalan mountains, I found none passing the winter in districts so high and cold. The winter range extends from the lowlands of both coasts up to possibly 7,000 feet above sea level. Indigo buntings are especially numerous between about 3,000 and 5,000 feet in the drier, deforested regions of the highlands and Pacific slope of Guatemala. At the end of October 1933 I found them in large, loose flocks in the weedy fields about Panajachel beside Lake Atitlan, 5,000 feet above sea level; here at this season they were far more abundant than any other finch, resident or migratory. In December1934 and January 1935 they were common in the coffee-producing zone of the Pacific slope between Colomba and Finca 'Moca,' at about 3,000 feet above sea level. . . .
"Although so gregarious in districts where there are extensive grassy or weedy fields, amid the heavy vegetation of the humid lowlands indigo buntings are more solitary; in clearings amid the rain forests I have generally met them singly or a few--rarely as many as half a dozen--together, in bushy pastures, old grainfields rapidly being overgrown with tall weeds and shrubs, and about the edges of the tangled thickets that cover lands which have enjoyed freedom from man's disturbance for a longer period. . . .
"On my farm, in the Basin of El General in southern Costa Rica, I seldom meet indigo buntings. But in the afternoon of April 11, 1945, a bunting clad in brown, without much doubt a female, came repeatedly to eat bananas at the feeding shelf in a guava tree beside my house--the only representative of the species I ever saw there. . . . After 6 days' attendance at the feeding shelf she left, probably during the night of April 16; and it is now nearly 3 years since I have seen one of her kind at my feeding-station. Incidentally, she provided my latest spring record of the occurrence of the indigo bunting in Costa Rica. . . .
"Most of the indigo buntings leave Central America during the first fortnight of April, and few are seen after the middle of the month."
For Costa Rica, as a whole, Slud (1964) writes:
During migration it occurs along both slopes, much more commonly the Pacific side and the central plateau, occasionally on the Caribbean side. It is met in largest numbers in the southwest, mostly in the upper tropical belt, and with fair regularity in the dry-forested lowlands in the northwest. The bird prefers "field" habitats, that is, open-country scrub, grassy and bushy pastures, abandoned agricultural lands, and low thickety edges. Usually it occurs in small flocks, close to or on the ground, that wander about perhaps within a circumscribed area or probably over longer distances. On the Caribbean side during the winter, at any rate, a small group may briefly reappear a few times in an area with suitable habitat, even in heavily forested regions. . . . The birds are mostly female-plumaged, usually with a blue individual or two or several with a touch of blue.
L. Griscom (1932) says, "Mr. Anthony writes that Indigo Buntings were especially noticeable at Sacapulas [Guatemala] in January and February, where they shared with P. ciris the honor of being the most abundant species, hundreds being flushed from the fields of dry weeds along the Rio Negro. In common with most, if not all, of the migrants from the United States these birds become excessively fat, just before they depart for the north."
In British Honduras, Russell (1964) notes that the indigos first arrive in mid-September and by late October are common. They frequent grassy areas, low huamil, and brushy plantation edges in flocks of 10 to 30. Many transients were seen at Half Moon Cay, April 16 - 24, and most have left the country by April 25. Two individuals banded in March at Middlesex by Nickell were recaptured the next year at the same locality.
After many years of ornithological experience in Panama, Dr. Alexander Wetmore writes Johnston of its occurrence there: "In its fall migration the Indigo Bunting comes regularly to western Panama, and a few continue through the isthmus to Darien and northwestern Colombia. As they seek the same type of cover in dense growths of weeds and grass in old fields and marshy spots that they frequent in late summer and early fall in the north, they are seen infrequently and remain little known. Males molt into the bright color of the breeding season in February and early March, and then change completely. Toward the end of March and in early April they appear in the open at the borders of thickets, and in cultivated areas in the fruit trees and shrubbery near houses. Here they often remain in the open, rather than fly to cover when startled. It is at this season that most of the rather few records of occurrence are made. Females, however, continue their skulking habits until they leave for the north."
From Montego Bay, Jamaica, Mrs. Audrey Downer writes Johnston: "Indigo Buntings wintering in Jamaica start arriving early in November. They are usually males in various stages of the blue plumage. In January the females and juvenals begin to arrive, and soon after this singing begins. Indigo Buntings have been seen in widely scattered areas throughout Jamaica, but are only known to congregate in flocks of from 50 to several hundred in two locations in the Montego Bay area at the western end of the island. The flocks build up gradually during the first three months of the year, reaching their peak from mid-March to mid-April, when the whole area pulsates with their song throughout the day. They then depart for their northern breeding grounds, and are all gone by the first week in May. During their stay in their winter quarters some birds complete their molt, while others undergo only a partial molt. The males outnumber the females four to one.
"The habitat favoured is a wooded area with low scrub ground cover. When frightened they dive for these low bushes. After a few minutes they emerge and fly into the trees to survey the situation before resuming feeding. They come readily to bird feeders baited with 'Budgerigar seed,' crushed corn, etc. They eat only the kernel, discarding the husk. They have also been observed feeding on dried logwood seeds, various weed seeds, and an occasional flying insect. Although they roost in naseberry, tamarind, and citrus trees, they do not appear to eat the fruit.
"In 1964 a banding program was started and 177 Indigo Buntings were banded in Jamaica. No recoveries have so far been reported."
Hybrids.--In the western part of its range the indigo bunting may hybridize with the lazuli bunting (Passerina amoena). Sibley and Short (1959) summarize their investigations by stating: "The Indigo Bunting (Passerina cyanea) and Lazuli Bunting (P. amoena) have formed a secondary contact in the plains as a result of climatic changes and men's activities, which have provided suitable habitat in a formerly unsuitable area. Over a broad area of contact and overlap specimens show that hybridization and backcrossing are occurring, and that both parental forms are present with the hybrids at some localities. . . . Measurements and weights of the specimens show that clear size differences exist between the parental forms, and that color pattern is correlated with weights and measurements in the hybrids."
On June 26, 1929, near Warren in Marshall County, Minn., W. J. Breckenridge collected a hybrid that was singing from the top branches of a dead elm. The song was identical with that of the indigo bunting. A nest in low bushes below the singing-tree was occupied by a typical female indigo bunting. William Youngworth (1932) also collected a male hybrid, on June 1, 1932, near the Niobrara River in Cherry County, Nebr. He says, "The Indigo Bunting is a fairly common bird in this region, and here also we found several Lazuli Buntings settled for the summer." The song was typical of the indigo bunting. Mrs. Harold R. Peaseley heard what she thought was the song of an indigo bunting at about noon on July 25, 1935, near Center Chapel, some 5 miles west of Indianola, Warren County, Iowa. The bird, in the top branches of a dead tree, proved to be a male lazuli bunting. She studied the bird for an hour and says, "Its behavior seemed to indicate a territory holding bird. It had three definite singing perches in the immediate vicinity of this tree and one across a small field in an Osage orange hedge. It drove a male indigo bunting out of its territory, and in so doing, the two birds came to rest for several minutes on a wire fence directly in front of us." She relocated the bird on July 27, but a thorough search failed to reveal satisfactorily the female.
Philip V. Wells (1958) watched two pairs along Leeds Creek at about 5,000 feet elevation in the Pine Valley Mountains in southwestern Utah between June 6 and Aug. 1, 1957. Vegetation was a closed stand of evergreen chaparral. Dwarf conifers formed a sparse overstory; along Leeds Creek, birch and willow were entwined with wild grape. Edge effects were provided by the stream, by a dirt road, and by some large clearings bordered by groves of deciduous oak. The two pairs of indigo buntings were spaced about half a mile apart along the road, in both cases near clearings. The favorite singing perches were the relatively tall birches along the creek, overlooking the cleared areas, but the birds also sang from junipers and foraged in all plant communities of the area.
During June one of the male indigo buntings was seen fighting with a male lazuli bunting. The two birds would take up singing perches on trees about 100 feet apart and sing back and forth until one took off in vigorous pursuit of the other. After about June 20, the lazuli buntings disappeared from the indigo bunting areas, although still sparingly present nearby.
Don Bleitz (1958), reporting on the indigo bunting breeding in Los Angeles County, Calif., found a male indigo mated with a female lazuli. The nest of this pair contained two bunting eggs and a cowbird egg. The eggs later proved to be sterile.
Why the indigo and painted buntings (P. ciris) do not
hybridize is something of a mystery. In certain parts of their
breeding ranges in the southeastern United States, as Norris
(1963) points out, the two species may be found in the same
general area. Parmelee (1959) sheds some light on this situation
in southern Oklahoma: "The Indigo Bunting. . .was both scarce
and local, and we found no situation where it and ciris
bred side by side, although conceivably they do just that in parts
of Marshall County. . . . there are significant differences in the
breeding behavior of the two species."
Indigo Bunting* Passerina cyanea
*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 1): 80-111. United States Government Printing Office