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Indigo
Bunting
Passerina cyanea
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 |
| Beecher (1942) |
thicket
unmodified woodland |
5 (nests)/7.08
acres
2/26.87 acres |
| Johnston (1947) |
forest edge
forest interior |
9-18 pairs/mile
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
shrubby field
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
Contributed by Wendell
Taber and David W. Johnston
*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
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