Index of Species Information

WILDLIFE SPECIES:  Sialia sialis

Introductory

WILDLIFE SPECIES: Sialia sialis
AUTHORSHIP AND CITATION : Sullivan, Janet. 1995. Sialia sialis. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ []. Revisions: 18 July 2013: DeGraaf, Richard M.; Rudis, Deborah D. 2001 citation corrected to DeGraaf, Richard M.; Yamasaki, Mariko. 2001. ABBREVIATION : SISI COMMON NAMES : eastern bluebird TAXONOMY : The currently accepted scientific name for eastern bluebird is Sialia sialis (Linnaeus) [3,59]. It is a member of the family Muscicapidae [59]. Subspecies recognized in the American Ornithologist's Union 1957 checklist (the last edition including subspecies) include [2]: S. s. sialis Linnnaeus, eastern bluebird S. s. grata Bangs, Florida bluebird S. s. episcopus Oberholser, Tamaulipas bluebird S. s. fulva Brewster, azure bluebird Eastern bluebird interbreed with mountain bluebird (S. currucoides) [46]. ORDER : Passeriformes CLASS : Bird FEDERAL LEGAL STATUS : No special status OTHER STATUS : Atwood [4] compiled state status lists of western landbirds; eastern bluebird was listed as of special concern in Montana and a "watch" species in North Dakota. Eastern bluebird was on the Audubon Society's Blue List (1986) in 1972, from 1978 to 1982, and of Special Concern in 1986 [74]. In a 1979 compilation of state lists eastern bluebird was listed as rare and/or endangered in Connecticut (1976), existing in limited numbers in Massachusetts, and uncommon and declining in New Hampshire [75]. It was listed in the South Dakota Natural Heritage Database as a species monitored by the South Dakota Department of Game, Fish, and Parks; apparently secure in the breeding season in South Dakota, though rare statewide and with cause for long-term concern. It was rated globally secure though rare in parts of its range [76]. In Canada, the eastern bluebird is listed as vulnerable in Manitoba, New Brunswick, Nova Scotia, Ontario, Quebec, and Saskatchewan [77].


WILDLIFE DISTRIBUTION AND OCCURRENCE

WILDLIFE SPECIES: Sialia sialis
GENERAL DISTRIBUTION : Eastern bluebirds breed from southern Saskatchewan east to southern Nova Scotia and south through the eastern United States [2].  In the West it occurs casually along the eastern foothills of the Rocky Mountains in Montana, Wyoming, and Colorado, more commonly in the Dakotas through central Nebraska, central Kansas, and central Oklahoma to central and southeastern Texas, and south to most of Mexico [41,70].  Eastern bluebird was listed in 1969 as a species whose present occurrence in Arizona is limited, unknown, or only suspected [64], although more recent work [46] lists Arizona as within its range. Eastern bluebirds winter in the middle parts of the United States south to Nuevo Leon, the Gulf Coast, and southern Florida, and rarely to western Cuba [2]. Ranges of subspecies are as follows: Florida bluebird:  Resident throughout peninsular Florida Tamaulipas bluebird:  Tamaulipas north to the Rio Grande valley in south-central Texas  Azure bluebird:  Transition zone from the mountains of southern Arizona south to Jalisco, Oaxaca, and Vera Cruz (Guerrero).  Winters south to northern Guatemala [2,6]. ECOSYSTEMS : FRES10 White-red-jack pine FRES12 Longleaf-slash pine FRES13 Loblolly-shortleaf pine FRES14 Oak-pine FRES15 Oak-hickory FRES39 Prairie STATES :
AL AK AZ AR CO CT DE FL GA IL
IN IA KS KY LA ME MD MA MI MN
MS MO MT NE NH NJ NY NC ND OH
OK PA RI SC SD TN TX UT VT VA
WV WI WY DC
MB NB NF NS ON PE PQ SK
MEXICO
BLM PHYSIOGRAPHIC REGIONS :    13  Rocky Mountain Piedmont    14  Great Plains    15  Black Hills Uplift    16  Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS :    K070  Sandsage-bluestem prairie    K074  Bluestem prairie    K075  Nebraska Sandhills prairie    K076  Blackland prairie    K077  Bluestem-sacahuista prairie    K081  Oak savanna    K082  Mosaic of K074 and K100    K083  Cedar glades    K084  Cross Timbers    K088  Fayette prairie    K089  Black Belt    K095  Great Lakes pine forest    K100  Oak-hickory forest    K104  Appalachian oak forest    K110  Northeastern oak-pine forest    K111  Oak-hickory-pine forest    K112  Southern mixed forest    K116  Subtropical pine forest SAF COVER TYPES :      1  Jack pine     14  Northern pin oak     15  Red pine     20  White pine-northern red oak-red maple     21  Eastern white pine     40  Post oak-blackjack oak     42  Bur oak     43  Bear oak     44  Chestnut oak     45  Pitch pine     46  Eastern redcedar     50  Black locust     51  White pine-chestnut oak     52  White oak-black oak-northern red oak     53  White oak     55  Northern red oak     64  Sassafras-persimmon     67  Mohrs (shin) oak     70  Longleaf pine     71  Longleaf pine-scrub oak     72  Southern scrub oak     74  Cabbage palmetto     75  Shortleaf pine     76  Shortleaf pine-oak     78  Virginia pine-oak     79  Virginia pine     80  Loblolly pine-shortleaf pine     81  Loblolly pine     82  Loblolly pine-hardwood     83  Longleaf pine-slash pine     84  Slash pine     85  Slash pine-hardwood    109  Hawthorn    110  Black oak    111  South Florida slash pine SRM (RANGELAND) COVER TYPES :    601  Bluestem prairie    602  Bluestem-prairie sandreed    603  Prairie sandreed-needlegrass    604  Bluestem-grama prairie    606  Wheatgrass-bluestem-needlegrass    608  Wheatgrass-grama-needlegrass    609  Wheatgrass-grama    610  Wheatgrass    611  Blue grama-buffalograss    612  Sagebrush-grass    708  Bluestem-dropseed    709  Bluestem-grama    710  Bluestem prairie    711  Bluestem-sacahuista prairie    717  Little bluestem-Indiangrass-Texas wintergrass    720  Sand bluestem-little bluestem (dunes)    721  Sand bluestem-little bluestem (plains)    731  Cross timbers-Oklahoma    732  Cross timbers-Texas (little bluestem-post oak)    801  Savanna    802  Missouri prairie    804  Tall fescue    809  Mixed hardwood and pine    810  Longleaf pine-turkey oak hills    811  South Florida flatwoods    812  North Florida flatwoods PLANT COMMUNITIES : Eastern bluebirds are found in a wide range of plant communities with open overstories and in openings within woodlands.  They are usually found at low elevations and are frequently observed in oak (Quercus spp.) woodlands [46].  In southern Michigan, oak-pine (Pinus spp.) woodlands frequented by eastern bluebirds were dominated by black oak (Quercus velutina), pin oak (Q. palustris), northern red oak (Q. rubra), white oak (Q. alba), eastern white pine (Pinus strobus), red pine (P. resinosa), jack pine (P. banksiana), and Scotch pine (P. sylvestris). Eastern bluebirds are also commonly found in old fields characterized by hawthorns (Crataegus spp.), black walnut (Juglans nigra), black locust (Robinia pseudoacacia), black cherry (Prunus serotina), chokecherry (P. virginiana), staghorn sumac (Rhus typhina), and multiflora rose (Rosa multiflora) [46].  Other eastern bluebird sites include the jack pine plains of Huron National Forest, dominated by jack pine, northern pin oak (Quercus ellipsoidalis), and scarlet oak (Q. coccinea).  Bracken fern (Pteridium aquilinum), blueberries (Vaccinium spp.), and sweet fern (Comptonia peregrina) are characteristic understory components [41]. Eastern bluebirds are also present in cutover and burned pine-oak woodlands [46] and in Wisconsin jack pine savanna.  The latter habitat type is maintained by frequent low-severity fire [68].  Eastern bluebirds are common in regenerating stands of central and southeastern oak-pine forests [17]. In western Virginia eastern bluebirds were observed in the Appalachian Mountains in lower and midslope forests dominated by scarlet oak, black oak, chestnut oak (Q. prinus), and white oak [11]. Wintering areas used by eastern bluebirds in the Apalachicola National Forest included pasture, open longleaf pine (Pinus palustris) woods, and pine-oak woodlands usually dominated by live oak (Q. virginiana) with Spanish moss (Tillandsia usneoides) [41].

BIOLOGICAL DATA AND HABITAT REQUIREMENTS

WILDLIFE SPECIES: Sialia sialis
TIMING OF MAJOR LIFE HISTORY EVENTS : The eastern bluebird is nonmigratory in many parts of its range.  This trait confers an advantage over migratory competitors for limited nest sites.  Eastern bluebirds and mountain bluebirds (Sialia currucoides) may occupy the same nest site in different years [46]. Spring Migration and Territory Establishment:  Eastern bluebirds and western bluebirds (Sialia mexicana) are similar in habitat requirements and exhibit interspecific territoriality [37], as do eastern bluebirds and mountain bluebirds in areas of sympatry.  Eastern bluebird territory size varies seasonally.  In Michigan eastern bluebird territories are largest in March and become progressively smaller through April, May, and June [46].  Nonmigratory males establish territories from February 20 to March 10.  Other males arrive and establish territories from late March to early April [48].  Females arrived after males in 1970, 1971, and 1974 [46].  Krieg [29] however, reported that in northwestern New York, the general pattern was a staggered arrival of male and female birds from mid-March to early June.  Some birds arrived already paired, others were unpaired [29].  In New York males choose territories in mid-March [60].  Each territory is established around at least one nest site and is usually expanded to include several potential nest sites [29].  Territories may be established as long as 6 weeks or as little as an hour before nest building occurs [71].  The males display and sing at several nest sites to attract females.  After a female accepts a particular site, she builds the nest out of dry grasses or other plant materials; sometimes several nests are built in different sites before eggs are laid in the final site [29,41].  Nest building usually takes 5 or 6 days, but may take 2 weeks or more; on occasion nests are built in 1 day or less and egg-laying commences immediately [71].  Eastern bluebirds do not exhibit strong nest-site fidelity [48]. Eggs:  Egg laying normally starts soon after the nest completion, but delays of more than a week are not unusual [71].  In southern Michigan egg-laying activity begins in early April, with complete clutches present as early as April 8.  Egg-laying activity (in a population) usually peaks the third week of April and again the third week of June. One egg is laid per day, usually with 1 or more days between eggs.  The typical eastern bluebird clutch is three to five eggs, occasionally six [41,71].  Incubation only begins after the clutch is complete [71].  The female usually does all the incubation, and is either fed by the male or takes short foraging trips [41,45].  Incubation lasts 13 to 15 days, and ranges from 12 to 21 days [41].  In New York first broods usually hatch at 14 days and later broods take 13 days, probably because of higher temperatures [71]. Development of Young:  In New York first broods hatch in early May.  The naked, altricial hatchlings are blind [60].  They are brooded almost constantly by the female for the first few days; brooding becomes more sporadic after feather growth commences, and ceases a few days before the young leave the nest.  Brooding intensity varies with weather [71]. Both parents feed nestlings and remove fecal sacs [22,60].  Fledging occurs from 15 to 20 days after hatching [41], most commonly at 17 or 18 days.  First flights are usually directly to a perch, and are 50 to 100 feet (15-30 m) in length.  Fledglings stay near the nest and each other, roosting together at night.  Parents feed the fledglings, who begin to find their own food about 2 weeks after fledging and achieve independence 3 to 3.5 weeks after fledging.  Widowed females often continue to raise the brood, often with help from unmated females and immatures (often members of earlier broods).  Widowed males attempt to raise broods if nestlings are well feathered; they also often have helpers [71]. About 10 days after the first brood fledges, the female usually builds a new nest (often in the same site) and lays a second clutch.  The male continues to feed the young of the first brood; when the second brood hatches the male and sometimes members of the first brood help feed the nestlings [29,60]. Multiple Broods:  Eastern bluebirds often produce three broods in one season in the central part of their range.  They are single-brooded on the northern periphery, and usually double-brooded elsewhere [40].  In southern Michigan there are two main nesting periods.  The spring nesting period peaks from April 6 to May 14 and is fairly synchronized (that is, most eastern bluebirds in the area are nesting at this time). The summer nesting period occurs from June 7 to July 23.  Eastern bluebirds nesting during the spring period usually attempt a second brood in the summer period.  However, there is an intermediate period, from May 15 to June 6.  Eastern bluebirds nesting in this period are usually only able to raise a single brood [47].  Nesting success is greatest in the intermediate period, but spring broods are bigger; overall more fledglings are produced from spring broods [45].  Two or three broods in a season is typical for many populations of eastern bluebirds; however, there are a number of reported instances of the production of four clutches or broods.  A single pair of eastern bluebirds produced four clutches in one season but only the first three produced fledglings [32].  In Alabama a male eastern bluebird successfully reared four broods in 1987.  This male apparently mated with two different females, raising two broods with each female.  It is possible that he was a helper rather than a parent with one of the females; genetic relationships were undetermined [65].  In northeastern Texas a single pair of eastern bluebirds (nonmigratory) successfully raised four broods:  four eggs, one hatchling, one fledgling April 14; five eggs, two hatchlings, two fledglings June 1; five eggs, one hatchling, one fledgling July 12; and four eggs, four hatchlings, and four fledglings August 22 [30].  Eastern bluebirds are predominantly monogamous (one male and one female are the genetic parents of all members of a brood) but polygyny has also been observed [23,24]. Fall Migration: The presence of fruit determines eastern bluebird distribution in winter [41].  In winter eastern bluebirds are found mainly in the southern half or two-thirds of the breeding range [71]. In southern Michigan probably close to 95 percent of eastern bluebirds migrate southward; in some areas all of the eastern bluebirds migrate [41,45].  The proportion of eastern bluebirds migrating decreases with decreasing latitude [41].  Southward migration of eastern bluebird flocks is usually leisurely as the birds search for food [71].  In New York parents and both broods remain together in summer and fall, then join larger flocks in the fall which move southward, stopping frequently where food is plentiful.  New York State eastern bluebirds travel as far south as Virginia and North Carolina [60].  In Tennessee eastern bluebirds that are present during the breeding season are usually nonmigratory.  They form small flocks of adults and immature birds in late summer and stay together most of the nonbreeding season [52]. Nesting Success and Productivity:  Pinkowski [45] reported that eastern bluebird achieved 56 percent nesting success in Michigan (nesting success is defined as the proportion of nests producing at least one fledgling).  Mean annual productivity for eastern bluebirds nesting in southern Michigan, over a 10-year study, was five fledged young per pair per season.  Estimated survival rates were 82 percent between fledging and independence, 33 percent between independence and the start of the next breeding season, and 50 percent thereafter (on an annual basis) [47].  In west-central Wisconsin nest boxes placed on managed lands, 45 eastern bluebird nests produced an average of 1.2 fledged young per nesting attempt [67].  Blowfly parasitism reduces nest productivity; it is a serious problem in some areas [73]. PREFERRED HABITAT : Nesting and Foraging Habitat:  Eastern bluebirds usually forage near the nest site.  In Ohio eastern bluebirds traveled up to 1,320 feet (400 m) from the nest on foraging trips [22].  Eastern bluebirds generally prefer early successional habitats or open stands.  In Arkansas several plots representing various stages of oldfield succession were surveyed for birds.  Eastern bluebirds were observed only in burned fields and in woody fields and not in more heavily wooded plots [58].  Within the oak-hickory (Carya spp.) forest, eastern bluebirds prefer to nest in savanna and savanna-like habitats such as pastures with scattered small trees and bushes, usually near a lake or other body of water [55].  In southern Michigan eastern bluebirds forage in open terrain [47].  They are most commonly found in old fields dominated by forbs and grasses with scattered trees and shrubs [44], oak and pine woodlands, open woods with brushy undergrowth, areas of tall weeds, roads and roadsides, recently plowed ground, and lawns.  Feeding perches adjacent to open areas are essential; rolling terrain is preferred over completely flat areas.  A dependable fruit supply is also important, particularly in early spring when insect availability is low [41].  In the northern sections of eastern bluebird range, key nesting habitat discriminators in order of importance include topographic relief, presence of evergreen shrubs, number of genera of deciduous trees, distance to nearest edge, and slope.  In the central sections, key discriminators were topographic relief, presence of evergreen shrubs, number of genera of deciduous shrubs, relative eastern bluebird densities, and number of genera of deciduous trees.  Nest box placement recommendations in relation to key habitat parameters for the northern sections of eastern bluebird range include presence of evergreen shrubs within a 100-foot (30 m) radius of the box and presence of 5 to 13 genera of deciduous trees within a 100-foot (30 m) radius.  Distance to the nearest edge should be between 86 and 452 feet (26-137 m) and slope should be between 0 and 8 percent. For the central sections it is recommended that there be no evergreen shrubs in a 100-foot (30 m) radius, none or only one genus of deciduous shrubs, and zero to four genera of deciduous trees within a 100-foot (30 m) radius [39]. Pinkowski [41] stated that dry, sandy, acid soil deficient in lime and organic matter creates near-optimum conditions for eastern bluebirds. In the Appalachian Mountains of western Virginia, eastern bluebirds were more common in areas of dense, low vegetation with scattered residual pole-sized trees and areas with open overstories and brushy understories.  Nests were in snags in recent clearcuts [11].  Conner and Adkinson [9] reported that eastern bluebirds prefer areas near clearcuts.  In Virginia eastern bluebirds were observed in clearcuts formerly occupied by oaks.  Nests were located in 1- to 2-year-old clearcuts which were sparsely stocked with young hardwoods (oaks, hickories [Carya spp.], black locust, sassafras [Sassafras albidum], and flowering dogwood [Cornus florida]) about 3.3 feet (1 m) tall; in 5-year-old stands moderately stocked with 6.6-foot (2 m) tall hardwoods; and one nest was located in a 12-year-old, densely stocked stand of 13- to 16.5-foot (4-5 m) tall oaks and hickories. All nests were in standing dead trees.  Eastern bluebirds were not present in 15-year-old stands [8,9]. In Illinois eastern bluebird densities in sampled habitats were as follows:  30 individuals per 100 acres (40 ha) in orchards, 34 individuals per 100 acres in edge communities with shrubs, 25 individuals per 100 acres in residential areas (lawns etc.), and 13 individuals per 100 acres in second-growth woods [25]. In central hardwood forests eastern bluebirds are common in regenerating stands (seedling-shrub stage) but are not present in later successional stages.  In loblolly-shortleaf pine (Pinus taeda-P. palustris) forests, they are uncommon in regeneration and sapling stages and present in old-growth stages but not present in pole and mature stands (possibly because of the presence of snags) [17]. In the Southeast, red-cockaded woodpecker (Picoides borealis) holes are used successively by other woodpeckers (Picidae), flycatchers (Empidonax spp.), titmice (Parus spp.), and eastern bluebirds.  Squirrels and chipmunks (Sciuridae) are also aggressive users of woodpecker holes [15].  Pileated woodpeckers (Drycopus pileatus) sometimes make holes too large to be used by some species, but eastern bluebirds use most of the holes [5]. Winter habitats used by eastern bluebirds usually contain fruit-bearing plants; these include open pine-oak woodlands, pastures (especially saw palmetto (Serenoa repens)-pineland threeawn (Aristida stricta) in the Southeast), open pine woodlands, and old fields [41]. COVER REQUIREMENTS : Nesting:  Eastern bluebirds nest in tree cavities, nest boxes, and crevices.  Many nests are built in abandoned woodpecker (Picidae) holes, knotholes, and cavities formed by decay and/or fire wounds.  Eastern bluebirds rarely nest in open situations.  In southern Michigan eastern bluebirds apparently prefer nest boxes to natural cavities but fidelity to one type of nest site is not strong.  Nest boxes may be more attractive than natural cavities because they are usually placed in suitable locations and have optimal dimensions.  Most changes from one type of nest site to another occur after nest failures [45,48]. Most natural cavities used by eastern bluebirds are in oaks or American elm (Ulmus americana) stubs [45,48].  Fire-scarred snags are also commonly used [42].  In South Carolina longleaf pine-loblolly pine stands, optimal d.b.h. of snags for cavity trees is 8 inches (20 cm) [27].  In oak-pine woodlands the average height of cavities in pine snags used by eastern bluebirds was 12 feet (3.6 m) and ranged from 1.7 to 55 feet (0.5-16.8 m).  Cavity depth averaged 7.8 inches (19.8 cm) and ranged from 3 to 19 inches (7.6-48.8 cm), entrance diameter averaged 2.4 inches (6.1 cm) and ranged from 1.5 to 5.2 inches (3.7-13.3 cm), and interior diameter averaged 3.6 inches (9.2 cm) and ranged from 2.2 to 6.3 inches (5.7-15.9 cm).  Entrance hole orientation does not affect nest site use, although there is a slight tendency to choose cavities facing southwest [41,42]. Foraging:  Perches near open areas, with an unobstructed view of air and ground and sparse ground cover, are favored foraging sites.  Dead branches are preferred over live ones, presumably for greater prey visibility.  Where natural vegetation is tall, eastern bluebirds prefer mowed areas to unmowed areas.  Areas with dry, nonfertile soils, low vegetation, and much bare ground are also favored [22,46]. Roosting:  Night roosting sites are commonly in pine, oak, or pine-oak woodlands with fairly large trees [41].  In winter, eastern bluebirds use nest boxes for roosting only on very cold days (in Tennessee they roosted in nest boxes on days when the temperature was 14 degrees Fahrenheit [-10 deg C] or lower).  Numbers of eastern bluebirds in nest box roosts ranged from 1 to 16 [50,51]. FOOD HABITS : A large proportion of the eastern bluebird diet consists of arthropods, most frequently grasshoppers and crickets, but also butterflies and moths, spiders, and beetles [46].  Preferences of captive eastern bluebirds included (in order) mealworms, crickets, grasshoppers, leaf hoppers, locusts, sow bugs, and stink bugs.  Wild eastern bluebirds also consume earthworms, May beetles, and caterpillars [41].  In Tennessee eastern bluebirds continue to hunt for arthropods in winter; even on cold days some arthropods, especially spiders, may be active on south-facing slopes. When air and soil temperatures are below 32 degrees Fahrenheit (0 deg C), insect activity (and therefore availability) is extremely limited [52].  In northwestern Tennessee droppings collected from nest boxes used as roost sites on the coldest days in winter contained only plant materials.  Insects are inactive on these very cold days [51,52]. Eastern bluebirds rely heavily on fruit in nonbreeding seasons when it is available.  Fruit is usually scarce in the early part of the breeding season.  In southern Michigan staghorn sumac and smooth sumac (Rhus glabra) fruits are frequently consumed [44,46].  Fruits of chokecherry, black cherry, multiflora rose, and flameleaf sumac (R. coppalina) are also common dietary components [41].  In northwestern Tennessee in winter, eastern bluebirds consume the fruit of sumacs (Rhus spp.), flowering dogwood, grapes (Vitis spp.), Japanese honeysuckle (Lonicera japonica), hackberry (Celtis spp.), rose (Rosa spp.), deciduous holly (Ilex decidua), pokeweed (Phytolacca americana), greenbriers (Smilax spp.), and climbing bittersweet (Celastrus scandens) [52].  In Florida fruits eaten in the nonbreeding seasons include those of greenbriers, smooth sumac, and juneberry (Amelanchier spp.).  Earthworms and caterpillars are also consumed when available [41]. Nestlings are fed caterpillars, grasshoppers and crickets, spiders, and (usually for older nestlings and fledglings) succulent early-maturing fruits such as mulberries (Morus spp.), raspberries (Rubus spp.), dogwood (Cornus spp.) fruits, cherries (Prunus spp.), and honeysuckle berries (Lonicera spp.) [46]. Foraging Techniques:  The most common foraging technique is dropping from a perch to capture already-spotted prey on or near the ground. Eastern bluebirds also forage by flycatching, foliage hovering, and rarely, gleaning [22,41,42,44,46]. PREDATORS : Most nest failures are due to predation and/or nest site competitors. In southern Michigan 23 percent of nest box failures was due to house wrens (Troglodytes aedon) puncturing eggs or removing them; 18.8 percent was due to raccoons (Procyon lotor) or other mammals, and 14 percent to weather [45].  In that study raccoons had to be controlled before successful eastern bluebird nesting occurred [41].  Eastern bluebird nestlings were killed and partially eaten by an eastern chipmunks (Tamias striatus) [38].  Red squirrels (Tamiasciurus hudsonicus) kill adult eastern bluebirds and rob eggs.  House sparrows (Passer domesticus) kill adult eastern bluebirds in nest boxes in competition for nest sites [41]. MANAGEMENT CONSIDERATIONS : Historical Populations and Range Expansion:  There has been speculation the genus Sialia evolved in the mountains of the southwestern United States; the eastern bluebird was probably abundant in the sparse pine-oak woods of Mexico and the southern states prior to European settlement.  Native American burning practices probably created areas suitable for eastern bluebirds [41].  From the early 1600's to about 1957 eastern bluebirds probably increased in eastern North America due to increased amounts of edge and oldfield habitats from human activity. Logging and slash burning create or enhance eastern bluebird habitat in many areas.  In the 1900's the range of eastern bluebird expanded into the Great Plains and more recently into the southwestern United States, possibly as a response to logging [70]. Population Status and Trends:  In the late 1950's and early 1960's eastern bluebirds declined to 17 percent of their previous numbers. Eastern bluebird numbers were reported as very low in Pennsylvania where they were formerly abundant [34].  James [20] referred to eastern bluebirds as a "disaster species" after the severe winter of 1961.  An unpublished 1964 American Ornithologists' Union report stated that the eastern bluebird was thriving in the wilder northern parts of its range but had suffered severely in more developed areas [69].  An analysis of Breeding Bird Survey (BBS) data for the years 1965 to 1979 indicated that eastern bluebirds declined significantly in the eastern and central regions.  Declines and increases varied by subregions, showing a decline when averaged over the entire continent [54].  Recoveries following declines in 1976 and 1977 were documented [56].  During the period 1978 to 1987, BBS data indicated significant increases over much of the eastern united States, with nonsignificant decreases in the lower Mississippi Valley. Trends for the entire period 1966 to 1987 are a mosaic of nonsignificant increases and decreases:  the southern United States had nonsignificant increases in populations of eastern bluebirds; more northerly regions had significant declines; and seven states showed significant increases. The authors pointed out that for bluebirds, selection of the interval from which trends are estimated can greatly affect perceptions of the trend.  Survey data can be greatly influenced by short-term effects, and population trends estimated from variable populations contain an environmentally induced "noise" component that is sometimes larger than the long-term trend [56].  Currently eastern bluebirds are uncommon to rare in the Northeast [14] but are either year-round residents or short-distance migrants.  However, eastern bluebirds have recently experienced a statistically significant increase in the region [61].   Causes of Declines:  Factors influencing eastern bluebird populations include nest site availability, predators, diseases, parasites, pesticides, and land use patterns [51].  James [20] analyzed Audubon Society Christmas Bird Count data and concluded that there had been long-term declines in wintering eastern bluebird populations from the mid-1940's to 1961 and that there was a strong correlation between cold winters and eastern bluebird declines.  The decline in eastern bluebird numbers in the 1950's and 1960's was attributed to severe winters (a late spring freeze in southern Michigan killed large numbers of eastern bluebirds in 1958), use of heptachlor to control Argentine fire ants, and to other biocidal agents [20,41,51].  There is no evidence that any of these factors changed in the 1970's with the possible exception of land use patterns.  Conversion of pasture into soybean production reduced the amount of suitable eastern bluebird habitat [51].  Extreme local declines [46] and extreme regional declines [51] have been noted in association with severe weather during 1976 and 1977. Low nesting success (including nest losses) has been attributed to competition with European starlings (Sturnus vulgaris), house wrens, and house sparrows, particularly where natural cavities are scarce.  Further losses are caused by blowfly parasitism and loss of nest sites [41,71,72]. Habitat Suitability and Nest Site Availability:  Many agricultural areas formerly occupied by eastern bluebirds are now suboptimal for eastern bluebirds because of a lack of nest sites [8].  In the southeastern United States, a common cause of tree death is lightning.  Lightning damaged or killed trees are quickly infested with beetles and other insects.  Many species of birds, including eastern bluebird, are attracted to these trees [28].  In open areas, particularly in residential developments, humans usually remove dead limbs and trees. Wooden fenceposts, once an abundant source of nest cavities for eastern bluebirds, have largely been replaced by metal posts [26]. Competition for Nest Sites:  A number of authors report that the availability of suitable nest or perch sites is the factor immediately limiting to populations of hole-nesting birds, including eastern bluebirds [5].  Niche overlap between eastern bluebirds and house sparrows in south-central Oklahoma was greater than would be expected by chance.  House sparrows have the potential to greatly influence the nesting success of eastern bluebirds [53].  Competition for nest sites has forced eastern bluebirds away from centers of human activity where house sparrows and European starlings are relatively abundant [8]. House sparrows were able to usurp seven out of nine nest boxes occupied by eastern bluebirds in a south-central Oklahoma study; they are sometimes able to kill the eastern bluebird occupant of a desired nest box [53].  The introduction of the European starling has greatly increased competition for natural cavities with large holes.  The aggressive and abundant European starling restricts eastern bluebirds to nest sites with small holes [41,72], especially where peak use of nest sites by European starlings coincides with the period in which eastern bluebirds are establishing territories and choosing nest sites.  In Maryland an investigation of competition between European starlings and eastern bluebirds was conducted in a residential area using a nest box with a large entrance hole.  This box was placed in an area containing nest boxes with small holes, many of which were used by eastern bluebirds. European starlings were so abundant in the area that they were probably saturating all suitable nest sites.  Trapping and killing of European starlings at the test box over the course of 3 years (a total of 335 European starlings) has reduced the numbers of European starlings seen at the box, and it is hoped by the author that in a few more years European starling populations may become low enough to reduce competition with eastern bluebirds for large-hole cavities [72].  In Kentucky, a study of 45 nest boxes over 3 nesting seasons evaluated eastern bluebird productivity in the presence of European starlings. Eastern bluebirds fledged almost as many young in 1983 when European starlings used 60 percent of the boxes as in 1985 when European starlings were excluded.  This result was attributed to the difference in timing of nest box use.  European starlings produced one brood in the nest box and eastern bluebirds produced broods both before and after European starling use each year.  No eastern bluebird nests were taken over or destroyed by European starlings in this study; it was therefore concluded that European starlings had little impact on eastern bluebird nesting success [12]. Other competitors of eastern bluebird include mountain and western bluebirds in areas of sympatry, particularly in the Great Plains grasslands where eastern and mountain bluebirds have expanded their ranges [46]. Nest Box Programs:  Nest box programs have become popular in many areas [41].  Pinkowski [45] reported that the nesting success rate (proportion of nests that produce at least one fledgling) was similar in natural cavities and in nest boxes.  Recommended dimensions for nest boxes are available [26,60,72,73].  Blowfly parasitism rates are similar in natural cavities and in next boxes, but nest boxes often have a higher number of blowflies per nest [73].  Nest boxes are most effective in open areas.  In south-central Oklahoma eastern bluebirds chose nest boxes in open areas with few trees [53]. Environmental Toxins:  In Wisconsin treatment of eastern bluebird nesting areas with paper mill sludge containing dioxin had no measurable adverse effects on growth or reproduction of eastern bluebirds as compared to untreated plots.  Eggs collected from treated study plots had dioxin levels ranging from 6.6 to 11 picograms per gram of egg (1 ppt).  Eastern bluebird eggs injected with 1,000 ppt of dioxin exhibited no toxic effects (i.e., eggs hatched at the normal rate), but eggs injected with 10,000 ppt did not hatch [63]. Management Recommendations:  In South Carolina pine and pine-hardwoods, 10 snags per 100 acres (40 ha) is optimal for maintaining eastern bluebird populations at 3.2 pairs per 100 acres (40 ha).  However, maintenance of all cavity-nesting species present at their average population levels would require 311 snags per 100 acres.  The principal cause of tree death and snag production in this area is lightning; currently these trees are rapidly removed for firewood.  The authors recommend severely limiting the removal of lightning- and insect-killed trees in order to provide more snags for wildlife use.  Other recommendations include retention of snags in clearcuts, leaving large snags instead of small ones, and protection of drainage systems by leaving strips of unmanaged forest along creeks to provide cavity trees [27].  Clearcuts in oak-hickory forest can be good nesting areas for eastern bluebirds provided that snags are present [26].

FIRE EFFECTS AND USE

WILDLIFE SPECIES: Sialia sialis
DIRECT FIRE EFFECTS ON ANIMALS : It is very probable that few eastern bluebirds die in fires [36]. Adults easily escape fire, and nests and nestlings are only vulnerable to severe fire that destroys nest sites. In Minnesota prescribed fire conducted during the breeding season was evaluated for direct effects on eastern bluebird nesting activity.  Nest boxes 4 and 4.6 feet (1.2 and 1.4 m) above ground were monitored on the day of the fire.  Flame lengths were 3.3 feet (1 m) or less.  Adult eastern bluebirds left the nest boxes as the fire front approached; one pair was observed hovering over the nest as the fire passed underneath the box.  The adults returned to the nest boxes when the fire had passed.  No eggs were harmed by this fire and there was 100 percent nest success (all eggs produced fledglings) for both boxes.  In the area the success rate for 23 nests was 93 percent [10]. HABITAT RELATED FIRE EFFECTS : The eastern bluebird is known as a fire-follower [1,16,35,62]; the low sparse vegetation on fresh burns and plentiful natural cavities caused by decay in fire injured or killed trees are important for eastern bluebird habitat [36,41].  In southern pine forests, fire retards succession, reduces midstory hardwoods and shrubs, and favors herbaceous vegetation; all of these effects enhance eastern bluebird habitat [16]. An important consideration is the effect of fire on food sources.  Fire often reduces understory fruit production [33].  There are conflicting reports on the effect of fire on arthropod populations [16].  The effects of fire on invertebrate populations may be transitory or long lasting.  There is usually an immediate decrease in invertebrates due to direct mortality and indirectly due to loss of food supplies and shelter.  In some instances flying insects are attracted by heat, smoke, or killed or damaged trees, and therefore populations of some species may increase during and after a fire.  Fires reduce the populations of most soil fauna (animals that spend most of their time on the forest floor or mineral soils).  The length of time of this effect varies with fire severity and postfire vegetation [36]. The Research Project Summary Effects of understory fire on cavity-nesting birds in Arizona pine forests provides information on prescribed fire effects in Arizona pine (Pinus ponderosa var. arizonica) forest where eastern bluebird was present. FIRE USE : Savannas and open stands are natural bluebird habitat that usually require recurrent fire for maintenance.  Prescribed fire is usually beneficial to eastern bluebirds, especially if it controls shrubs and understory hardwoods [46].

REFERENCES

WILDLIFE SPECIES: Sialia sialis
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