The Blue Birds Winter Nest

Supplanting attacks are the most frequent form of aggression. Once individuals make contact, both combatants may strike one another with their wings, grab feathers with beaks, and grapple with their feet at each others' bodies. Individual bluebirds also head-peck during fights. Head pecking appears highly motivated in that it is often done rapidly as if to a staccato rhythm PAG per obs.

Fights are often extended, with combatants falling to the ground, paying no attention to their surroundings. Males are more likely than females to attack potential nest-site competitors Belser ; females seem somewhat more willing than males to attack species with similar foraging requirements. Most interspecific aggressive encounters occur during the breeding season. During migration, when Tree Swallows Tachycineta bicolor pass through southern and middle portions of eastern bluebird breeding ranges, chases and fights break out between Tress Swallows and Bluebirds PAG.

On the breeding ground, early in the breeding season, fights are common. Threat displays include Facing, Gaping, and Wing-Flicking see below. Appeasement displays include Turning-Away and Fluffed Posture. In Turning-Away, eastern bluebirds fluff feathers, then turn their heads away from the opponent opposite-sex members of pair, or combating males.

Appeasement displays occur during territorial disputes and agonistic encounters between pair members. When in a Fluffed Posture, individuals retract their heads and fluff their feathers. The Fluffed Posture appears similar to resting, and during nesting cycle, either member of pair may assume the posture. In Facing, one individual turns their head to face their opponent.

Facing usually occurs when an individual distance is violated. Gaping is like Facing, except that beak is open.

During high-intensity Gaping, sleeks head and neck-feathers and leans toward approaching bird. In Wing-Flicking Wing-Waving , bird is perched in oblique position and flicks both wings rapidly out to a plane that is level with body. May fan tail; display accompanied by Warbles and Chatter see Sounds: Gives Wings-Out Display when facing opponent: Legs fully flexed, body horizontal, plumage sleeked, wings out horizontally to side; never given to conspecifics.

Usually followed by Alarm Scream and aerial attack on predator or potential predator. Gives Head-Forward Display while facing opponent: Body horizontal, head retracted, tail slightly lowered, legs flexed, body feathers sleeked; Gaping see above , bill snap see Sounds: Two bill-raising postures Krieg In Oblique Bill-Up Display, body is oblique with head, tail in plane with body, tail slightly raised.

In Horizontal Bill-Up Display, legs extended, neck stretched, head and bill pointed upward; black chin-stripes of both sexes are exposed to opponent's view. Most frequently, males are aggressive to males; females are aggressive to females. Both adults can be aggressive to juveniles of either sex. Instances of male-to-female and female-to-male aggression also occur, but rarer than intrasexual aggression. In a comparative study during , male aggression to females was distinctly more frequent in Athens, GA populations than Clemson, S.

Carolina populations Gowaty, unpubl data , perhaps because during females fertile period, females were foraging off territory more often in Athens, GA than in Clemson, SC. The differences may have been due to differences in arthropod abundance with greater availability in Clemson, S. Experimental evaluations Gowaty indicate male-male aggression most likely serves to protect threatened paternity, because male-to-male aggression is greatest when females are fertile, whether for first or later nesting attempts.

Males are aggressive to other adult males usually in defense of paternity; resident males are most likely to respond aggressively to other males when females are fertile Gowaty Experimental studies have shown that male-to-female aggression occurs infrequently in some populations but not at all in others Gowaty , Gowaty and Wagner Male to female aggression is facultative occurring during the breeding season as an optional aspect of pair formation and initiation of breeding cycles.

For example, in a systematic observational study controlling for time within the nesting cycle and year of observation and methods, rates of male-to-female aggression were significantly higher in Athens, GA, than in Clemson, SC PAG unpubl. In experimental field tests in Clemson, SC, male aggression against females was infrequent Gowaty , Gowaty and Wagner In Pennsylvania, males chased females most during pair formation Krieg , but actually attacked females most during nest-building, when males may have been attempting to condition females' ranging behavior or perhaps even attempting to dissuade them from recruiting to the cavities the aggressive males were defending.

Females are also sometimes aggressive to males. An aspect of pair formation: Experiments revealed that aggression of adult bluebirds to same-sex conspecifics is situation dependent.

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Aggression is induced and modulated by the time-dependent threat a particular conspecific. Experiments indicate female-female aggression protects nests from conspecific nest parasitism Gowaty and Wagner and, in S. Carolina was unlikely to occur in contexts in which paternal contributions to parental care were threatened by interloper females Gowaty and Wagner Earliest report Pettingill indicates that an intruder female won a fight with an already-crippled resident female, took over nest cavity, and bred with resident male.

In New York in a systematic observational study during breeding season, 1 female was supplanted another 41 times within 1 h Krieg Severe wounding, maiming, or death of females as a result of female-female fights noted in many populations Nice , Pettingill , Laskey , Blake , Gowaty and Wagner and personally observed PAG. Anecdotal records suggest that after having over-wintered with fathers with little or no agonism, yearling males are aggressively repelled from breeding territories of fathers and their mates in subsequent breeding season Pinkowski e.

Females are aggressive to juveniles usually when they are feeding nestlings in earlier broods; rarely occurs during latest broods PAG, JHP unpubl. Sometimes on wintering grounds 1 or other sex is excluded from access to food or roosting sites by aggressive postures, calls, or motor acts of others. Experimental evaluations of variation in aggression in breeding territories during winter are consistent with year-round defense of nesting cavities Plissner and Gowaty Juvenile-juvenile aggression, usually chases and supplants, rarely between siblings, usually between juveniles of different ages, may function in establishment of dominance hierarchies in nonbreeding season flocks Plissner Adult males and females are often aggressive to fledglings and young of the year in juvenile plumage PAG per ob , but only when adults are feeding nestlings in first or second broods.

While feeding nestlings in latest broods of the season, adults are seldom aggressive to birds of either sex in juvenile plumage. Gowaty and Plissner speculated that earlier season aggression of adults to bluebirds in juvenile plumage reflected the cost of foraging competitors on their territories. Aggression intensity of male bluebirds during females' fertile periods to mounts of birds in juvenile or adult plumage are consistent with the information associated with the orange breasts of adult males Ligon and Hill Systematic observations of agonistic encounters between wild pairs of females and males during courtship indicate that neither sex completely dominates the other.

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In some pairs, females were more aggressive; in others, males. In this migratory population, pairs that were already paired upon arrival showed little aggression Krieg Although dominance hierarchies among sib-groups have been documented Krieg , no clear dominance hierarchies have been documented in wild birds Plissner Adult bluebirds defend the area around the nesting cavity; bluebirds use the nesting territory for mating, nesting, and feeding.

Thus nesting territories include cavities. Home range sizes, sometimes called territories, 1. Territory sizes decrease as the nesting season progresses, perhaps in response to changing insect availability or other selection pressures, such as male mate-guarding or provisioning of nestlings, that keep adults nearer cavities Gowaty and Wagner , Gowaty et al.

About Bluebirds

Territories in burned or lumbered areas are smaller than territories in old fields or in pastures and orchards, probably because of ease of foraging and availability of perches. Territory size can be substantially reduced by increase in number of available nesting cavities within an area PAG: Placing nesting boxes 10 m apart along fences experimentally reduced territory size. Eastern bluebirds establish and maintain their territories by singing loudly, patrolling boundaries both males and females , and directing aggressive defense at interlopers and potential interlopers.

Bluebirds are also aggressive to other cavity nesting species, sometimes directly usurping nests from Brown-headed Nuthatches see video and attempt usurpation from Red-cockaded Woodpeckers. When resident bluebirds attack and supplant interlopers, most territorial disputes are settled. Either sex of adult may perform these attacks, which are usually directed at same-sex adult conspecifics.

See Agonistic behavior, above. Bluebirds defend feeding areas during the winter, when in flocks of 2—30; this defense is less intense than during the breeding season. Family groups and overwintering pairs defend areas around nesting cavities in areas where resident all year.

Anecdotal reports indicate competitive exclusion of females from small roosting sites by several cohabiting males. When roosting at night or resting during the day, the nearest distance between neighboring adults is about 0. Generally eastern bluebirds are socially monogamous in S. During — in S. Carolina, from observation of nesting attempts in which all adults were uniquely color-marked, social monogamy equaled Carolina suggest sex ratio parity in many years, male bias in others.

Males broker the access of females to their nesting cavities.

Self-Maintenance

Males first perform a nest demonstration display Figure 4 for prospecting females. Males may reject potential mates by removing nesting materials of females who are building Gowaty per sobs.



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The duration of pair bonds is associated with previous nesting success. Pairs remain together between seasons in migratory populations more frequently than expected on the basis of separate probabilities that individuals will return and return to the same place Pinkowski d. Feeding of females by males is a regular aspect of breeding biology in migratory populations, but it is often rare or absent in facultatively migrant or nonmigrant populations Thomas , Hartshorne Males also attended fertile females longer and followed them more often than they did non-fertile females.

Carolina, males guard females more strongly in multicavity territories than in single-cavity territories, an effect not found in an Ontario population Meek and Robertson a , where interspecific interactions with Tree Swallows are common. Females who are off territories most during fertile periods have significantly more young from extra-pair sires than females who remain on their territories more often. Male may use cues in female's behavior, such as how often she is off territory, to guide guarding decisions. Male's tendency to be aggressive to other males is greatest when female is fertile Gowaty , so another behavior that may increase paternity certainty is male-male aggression.

In comparative studies of populations differing in food resources, males guard mates more strongly where females must forage more often off their territories for more sparsely distributed food PAG. Copulation seldom observed; seems surreptitious. Many copulations occur in the hour after an egg is laid, once egg-laying has begun; birds copulate on perches and sometimes within nesting cavities Hartshorne Copulation sometimes preceded by Peeps see Sounds: Male mounts female's back; cloacal contact may or may not occur; copulations completed within 1—5 s.

Females initiate copulations by assuming Solicitation Posture. In New York during copulations, females utter low Peeps see Sounds: Carolina and Georgia, females may be silent PAG. In Clemson, SC, within-pair copulations occur as early as 8 d before first egg is laid and up to 6 d after Gowaty et al. Carolina, aggressive copulation is rare PAG.

One reliable observation was between captive bluebirds that were confined to a small cage with no opportunity for the female to escape Krieg Aggressive copulation is uncommon in eastern bluebirds. From Gowaty b and Gowaty and Bridges b.

Bluebirds' Winter Waterhole

Eastern Bluebirds suffer from competition with European Starlings and House Sparrows for nest sites, but the thousands of nest boxes that have been erected appear to off-set these detrimental effects see link below for nest box designs that exclude starlings. Usually 4 to 5 eggs with a range of 3 to 7. In Tennessee first clutches are commonly laid in March, last clutches in July or August.

The young are fed by both parents and fledge in 15 to18 days. Young produced in early nests usually leave their parents in summer, but young from later nests frequently stay with their parents over the winter. Bluebirds depend on naturally occurring cavities, tree cavities excavated by other species, or nest boxes. The female builds the nest of grasses, and lines it with finer material. Nest Box Instructions here. The Eastern Bluebird is a common permanent resident across the state though some individuals may migrate further south in winter.

Populations appear to be stable, but vulnerable in especially severe winters. Dynamic map of Eastern Bluebird eBird observations in Tennessee. Best places to see in Tennessee: Eastern Bluebirds are found in every county in the state. Many state and local parks have "bluebird trails" with multiple bluebird houses. Tennessee's Woodworking for Wildlife page with nest box instructions.