Behavior

Feeding adults hop on ground and branches. Flight is direct. In territorial encounters, males glide and use a slow, fluttering “butterfly flight” with wings held at right angles to the body, and quivering in position, in approaching another male.

Not reported in detail. Scratch head with foot over wing, stretch, bathe when surface water is available, and occasionally sunbathe.

Roosting behavior is not well known. In breeding season birds seen to fly into dense Rubus bushes at dusk, in winter roost in tall grass, marshes and in trees (Taber and Johnston 1968, RBP). In captivity, birds perch with fluffed posture and with head tucked under scapula feathers, and not in contact with other buntings (RBP).

No detailed observations available on proportion of time spent in alternative behaviors.

Breeding birds are active from first light (male song) and feed throughout the day. Males sing all day but deliver most songs in early morning and often feed and sing within same minute of observation. In migration males occasionally give outbursts of a loud song or two. Males conspicuous high in wooded vegetation, females secretive and live in shrubs, mainly within 1 m of ground. In winter, buntings feed throughout the day, leaving roosts within an hour after sunrise and returning about sunset and do not sing.

Physical Interactions

Early in the breeding season, shortly after arrival (and sometimes later when intruders enter the territory), mated males chase intruding males in their territory, giving buzzy cheet calls and supplanting them on perches. Some males grapple in the air and fall to the ground, feet engaged, one or both sing loudly and continuously (RBP). Males establish territory by singing and chasing neighboring males. Intruding males chased throughout the season. Older males sometimes replace younger males that arrive and settle earlier on their old territory. Males sometimes attempt to take over an occupied territory by chasing the resident; in these flights, the "pretender" often sings more than the resident (Carey and Nolan 1979).

Threat And Appeasement Displays

Males and females aroused near the nest rapidly turn on perch side to side, twitch tail side to side, and give chip calls (Taber and Johnston 1968, RBP). Males aroused or alarmed stand erect, body plumage compressed, head held high and feathers erected in a crest, tail raised and flicked from side to side; often accompany the posture with chip calls (Taber and Johnston 1968, Emlen 1971b). Males in vigorous song attack an intruder (or a speaker broadcasting a bunting song) with no display, hitting the intruder (or a dummy placed near the song speaker). Males sometimes attach by hopping toward the intruder, wings erect over back, body plumage compressed (Emlen 1971b). Males hesitant in attack may approach, crouch, fluff the body plumage, retract the head, tilt the beak upward, and lower and flutter the wings, and sometimes slowly move head away from intruder, then face the intruder and move head to the other side (Thompson 1965), perhaps in self-conflict in whether to attack or escape. Song in this context is very soft and heard only within a few meters. Males may perform a slow fluttering flight toward the intruder, especially in initial attack. Intruder often faces away from resident male, intruder's submissive status indicated by a fluffed plumage, head retracted, and bird immobile, often with tink calls (Emlen 1971b). Usually one bird continues to face the other and the other male retreats without physical contact. Rising levels of conflict over establishment of territories early in the breeding season sometimes lead to two males grappling on the ground, with feet interlocked, and one or both males in song (RBP). Fights sometimes severe.

Nonbreeding buntings are not territorial; in winter and in migration when feeding they remain at least 30-50 cm apart in flocks.

Breeding territory size averages 1.4 ha (George 1952, Taber and Johnston 1968). In s. Michigan territory size varies from 0.4 to 8 ha (RBP), depending on habitat; smallest along the shrubby and weedy edge of woods and old fields, and largest in shrubby swamps. Females generally nest on territory of their social mate (Payne and Payne 1989 but may nest in an area with no resident male or in an area defended by another male. Nesting males and females feed directly on their territory and sometimes feed off the male's territory.

Mating System

Most breeding males have a single female on their territory, but 15% of the breeding males have ≥ 2 females, either at the same time or serially over a season (Carey and Nolan 1979, Payne 1982, 1989, Payne et al. 1988). Mating is monogamous in a social sense, insofar as one male and one female usually occupy the same territory. In a genetic sense, mating system is less well defined, because birds sometimes mate outside the social pair. The number of females that settle on male territories is well described by a random model of distribution, with 0, 1, 2, 3, or 4 females on a territory, suggesting that females settle independently of whether the male is already mated, and a female does not pre-empt another from mating with him; no regular observations of females fighting. Nevertheless, in Michigan conflict observed when a new unbanded female mated early in season with a returning male on his old territory; she nested and laid eggs, then the banded female of the previous year arrived; she repeatedly chased the unbanded female who then abandoned her nest; the banded female then nested (Payne 1983b, LP).

First-year males and older adults differ in plumage. First-year and older males arrive at nearly the same time in spring and hold territories the same length of time in summer. Cloacal protuberance of first-year males is as large as in older males; both peak and plateau about a week after the first females arrive in spring. First-year males with more blue in breeding plumage wait a shorter time to attract a nesting female than first-year males with less blue in plumage; this variation in plumage accounts for only 2% of variation in time from male arrival to female's first nest. Number of mates for the mated first-year males and adults is the same, but not all first-year males have a nesting female (RBP). Nearly all first-year males and adult males copulate, as shown by copulation markers (plastic microspheres inserted into male cloaca and recovered in female cloaca). First-year males are effective in sexual behavior; their sperm count is low in first week on breeding grounds, then sperm count is equal to that of adult males the rest of spring and summer (Quay 1989). First-year males are about as likely to copulate and to fertilize eggs as older adult males (Westneat 1987b, 1990, Quay 1989).

Pair Bond

No evidence of an effect of behavioral, morphological, or genetic similarity of partners on mate choice. Females do not seek out—or avoid—a male that already has a mate. Buntings that returned to breed on their natal area did not seek out or avoid mating with other locally-born birds. Females do not tend to mate with males with a song like their father's song, nor to avoid them. Females mate at random with respect to male song, allowing for the number of males with the song theme (Payne et al. 1987, Payne and Westneat 1988, Payne 1991, 1996, Payne and Payne 1993b, 1996).

Male follows female closely during nest-building and laying period, otherwise usually does not attend her. Males do not sing often in courtship but they accompany their prospective mate, stay within a few meters of her, and chase other male buntings and sometimes other small songbirds foraging near the female. Female generally is not physically attacked by mate; occasionally male forces copulation with his mate. Female sometimes visits other males on their territories before and during egg-laying (Payne 1983a, Payne and Payne 1989), or feeds on territory of a neighboring male, or on a common feeding area. No courtship feeding observed.

In copulation, first the female crouches on a perch, calls twitter ti-ti-ti-ti, quivers wings, holds tail up; male flies to female, mounts her dorsally from rear, in flight, without song or other displays; female moves tail over her back during copulation. Copulation (cloacal contact) lasts about 2 s. Male often gives buzz during copulation, then flies from the female. Female often preens after copulation. Copulations are repeated 4—10 times/10 min (Westneat 1987a, RBP).

Courtship on ground seen less often. Male crouches with neck retracted and plumage sleeked, wings slightly spread in front but tips crossed over his back. In this posture he walks or struts rapidly in small circles (0.5 m diameter) in front of the female with no vocalization. The behavior occurs 1-2 days before laying (Taber and Johnston 1968, M. Carey and L. Payne unpubl. observ.).

Female settles on a male's territory within a day or two after she arrives in spring (Carey 1982). Pair usually remains together and may rear as many as three broods in a season. Less often, female diperses to another territory and mates with another male. Some females nest with three males in a season (Westneat 1987a, 1988a, b, RBP). In two cases both male and female of a pair moved across several territories and bred together again. Although most females stayed on a territory through the season, 11% of pairs separated after a nesting attempt, when the female moved to a new territory and took a new mate. Females were more likely to move to a new territory when they were successful than when unsuccessful in the earlier nesting attempt (Payne and Payne 1996). Females even known to take fledged brood with them; new male did not feed her brood; females often breed with new male after brood is independent (Payne and Payne 1996).

Within a breeding season, females are less likely to change territories than they are between seasons. In Michigan, when a male dispersed from a territory and another male took it over, the new male did not help the female rear the young. In one case a late-arriving first-year male (YXBS) actively fought with an adult male (GOXS) that had a territory, a nest and an incubating femal; the adult disappeared and YXBS held the territory that year and the next. Female reared the brood unaided by the male, who did not even give alarm calls near the nest; the bunting that fledged from the nest survived under female-only care and returned to breed in the next year (RBP).

Extra-Pair Copulations

A few (2-13%) copulations observed in the days before laying are extra-pair, the female coupling with a male other than her mate (Westneat 1987a, Payne and Payne 1989 . Genetically effective copulations may occur in early morning near the time of laying and ovulation; nearly all observed copulations have been later in the day. Extra-pair copulations are solicited by a female either on her territory or on the territory of a neighboring male, or are forced by an intruding male (Payne 1983b, Westneat 1987a, LP, RBP).

Many offspring are fathered by males other than the female's mate, as indicated in molecular mismatches between the offspring and the resident male attending the female and offspring (Westneat 1987b, 1990, Westneat et al. 1987), and in the higher heritability estimated from body size of offspring and maternal parent compared to the body size of offspring andher mate (Payne and Payne 1989 . Parentage assessed by DNA fingerprinting in one population indicated 22 (35%) cases of 53 offspring had bands (genetic markers) not shared with their behavioral father, and none had markers not shared with their behavioral mother. The observations indicate extra-pair fertilizations by a neighboring male for 35% of a female's young. In three broods, all nestlings were sired by a male other than the resident male. In six of the 22 excluded offpspring, a territorial neighbor male was the genetic father; in other cases the genetic father was uncertain. Finally, when ages of resident males were compared, the first-year males were less likely than the older adults to be cuckholded (14% vs. 41% of offspring in nests on their territory) (Westneat 1990). In another population, the genetic parentage, as assessed by allozymes, indicated fewer extra-pair offspring. Only 14.4% of 257 offspring were sired by another male in this study; when adjusted for the probability of detection (0.4) in this method, these data give an estimate of 42% extra-pair fertilizations. In this study, resident first-year males were more likely than older adult males to be cuckholded (36.8% vs. 12.5% of offpsring) (Westneat 1987b, Westneat et al. 1987).

The higher proportion of extra-pair matings as estimated in genetic comparisons of parents and offspring, than as observed in extra-pair copulations, deserves further study. Genetically effective copulations may occur when females visit the other males' territories and are inconspicuous, rather than the more conspicuous copulations observed when an intruding male meets the female on her own territory.

When markers (colored microspheres) were introduced experimentally into male cloacae, more than one kind of marker then appeared in a female's cloaca. These markers indicate a female had sexual contact with >1 male (Quay 1988). For males, nearly all first-year and adults transferred cloacal markers into one or more females (Quay 1989).

Sociality

Solitary in breeding season, loose flocks in migration and winter. No aggressive behavior in winter, and sing in migration only when near the breeding destination. Breeding birds often live near each other, perhaps attracted to each other for extra mating opportunities; birds are absent from apparently similar habitat patches in the same area. Male remains nearby the female during the days before she completes laying the clutch. Not social by other critiera, no coalitions seen between males or between females, and only a loosely recognized pair bond. Play not observed; young do not pass food to siblings, nor do they allopreen or roost in body contact.

Male and female in a pair remain together with little interaction. Long-term pair bonding is difficult to distinguish from mutual attraction of male and female to the same breeding territory (Payne and Payne 1996).

Interactions With Other Species

In the northern Great Plains where they hybridize with Lazuli Buntings, Indigo Buntings are often interspecifically territorial, as males of each species chase other males from their territories (Emlen et al. 1975). In Oregon, Indigo Buntings occasionally appear in spring, establish territories and remain through summer, the males pair with the female Lazuli Buntings, and some mixed-species pairs are successful in rearing a brood (Marshall et al. 2003). In southern parts of range they sometimes compete for territories with Painted and Varied buntings (Wauer 1973).

Interspecific territoriality with Painted Buntings (Forsythe 1974) or the larger but visually similar Blue Grosbeaks (Passerina caerulea) is uncommon; Indigo Buntings sometimes compete for territories with Pained Buntings and Varied Buntings (Wauer 1973 . Cerulean Warblers (Dendroica cerulea) chase male Indigo Buntings from forest edge when establishing their territories; buntings ignore the warblers (RBP).

In winter in Colima, Mexico, Indigo Buntings occur in flocks side by side with Lazuli Buntings, Varied Buntings, and Painted Buntings. In Mexico (Veracruz) and Belize, Indigo Buntings usually occur and feed in single-species flocks, and not with other kinds of seed-eating birds. In Jamaica they often feed with grassquits (Tiaris spp.). During daytime buntings disperse and feed individually or in small groups, a few chase and give buzzy cheet calls. Winter birds do not sing, and they are not territorial. Buntings roost at night in groups of hundred and thousands in tall grass and bushes near ricefields (Rappole and Warner 1980, Downer and Sutton 1990, Howell 2005, RBP). No observations on individually marked birds in winter.

Little information: loss of brooding females, eggs and young frequent but almost always without direct evidence of identity of the predator. Predators at the nest are thought to be raccoon (Procyon lotor), oppossum (Didelphis virginianus), skunks (Mephitis mephitis), mink (Mustella vison), red fox (Vulpes vulpes), feral cat and Blue Jay (Cyanocitta cristata). Long-tailed weasel (Mustela frenata) know to take fledged young.

Nests that fail owing to predation are identified by appearance. Some nests are pulled from supporting vegetation; others are emptied with no damage except the nest lining in disarray, apparently grabbed by the young bunting as a predator removed it from the nest. As we watched a deserted bunting nest with a cowbird egg, a raccoon approached, and it took the egg without disturbing the nest. Snakes sometimes take eggs or small young without disrupting the nest structure.

In Missouri, where nests were monitored by videocameras, 8 (53%) were taken by a predator (snakes at 5 of 6 of nests where a predator was identified), 5 were abandoned, and 13 (30%) were successful; nests without camera monitors had higher predation (Thompson et al. 1999). In Indiana, about 75% of all nests failed owing to predation (Carey and Nolan 1979). In Savannah River, SC, predators accounted for 83.6% of all nest failures (Weldon and Haddad 2005).

Adult buntings, especially females, give rapid alarm chip-chip-chip calls when humans approach either a nest containing large nestlings or recently fledged brood. The adults fly toward the predator just over the level of the nest, flutter off appearing injured, then fly away when the predator is distracted a few meters from the nest. Chipping calls attract the mate, who approaches and chips; buntings on neighboring territories do not join and form a mob. Buntings ignore dogs and Blue Jays near the nest, but become quiet and dive into dense cover when raptors appear nearby (e.g. American Kestrel, Falco sparverius, Cooper's Hawk, Accipiter cooperi, LP, RBP).

Indigo Buntings avoid predation by concealing their nests. Nests in abrupt and closely managed edges of agricultural fields are more likely to be taken by a predator than nests where plant succession provides a variety of plant heights and cover (Suarez et al. 1997). In Michigan, nests in Rubus were often built near the edge of the bush, concealed by leaves both above and below, and were less visible from outside the bush than inside (observers often found nests by peering from inside the bush). In fieldwork to test the flushing distance and vegetation concealment of nests, females flushed (escaped) more quickly when nests were less concealed (Burhans and Thompson 2001). These observations suggest that females site the nest to protect themselves from predation.