Sialia sialis

Eastern Bluebirds, familiar birds in open, deciduous woodland habitats of eastern North America, are easily observed as they forage for insects from conspicuous perches. While often thought of as gentle birds, they can be pugnacious in defense of the cavities in which they nest. Competition for cavities from European Starlings (Sturnus vulgaris) reduced the population of bluebirds in the mid-20th century. Fortunately this decline has been reversed by the work of volunteers who erected hundreds of thousands of bluebird nesting boxes (Gowaty, and Plissner 1998).

DISTRIBUTION. During the 1987-1992 field work seasons of the TBBA project, atlasers found confirmed breeding evidence for Eastern Bluebirds in 412 blocks, probable breeding evidence in 301 blocks and possible evidence in 144 blocks. The densest concentration of breeding records occurred east of the 99th meridian and north of the 29th parallel in the Pineywoods, Coastal Prairies, Post Oak Savannah and Blackland Prairies and eastern Rolling Plains eco-regions (see the region map in Lockwood and Freeman [2004]) .The distribution of blocks with breding evidence becomes more scattered to the west and south of this area. North American Breeding Bird Survey (BBS) data show relative abundances in Texas as high as 3-10 bluebirds per 40 km (25 mi) route (Sauer et al. 2008). In Oklahoma atlasers found breeding evidence in all parts of the state except the Panhandle (Carter and Duggan 2004).

BBS data show the breeding range of Eastern Bluebirds extending from southern Manitoba south to the Gulf Coast and west from the Atlantic Coast to the central Great Plains (Sauer et al. 2008). In winter the breeding population north of a line from southern Massachusetts through St. Louis, MO, to the Kansas-Oklahoma border moves south in the breeding area and into some areas nearby.. Other pzopulations breed in evergreen oak and pine habitats of the highlands from extreme southeast Arizona, through western, central and southern Mexico, to northwest Nicaragua (Howell and Webb 1995, Gowaty and Plissner. 1998, Lockwood and Freeman 2004, Corman 2005).

SEASONAL OCCURRENCE Eastern Bluebirds are present all year in Texas. They breed from mid-February to late July, based on young in a nest as early as March 6 and egg collection dates to July 15. Eastern Bluebirds are common to uncommon as migrants and winter residents east of the Pecos River (Oberholser 1974, Lockwood and Freeman 2004).

BREEDING HABITAT. Eastern Bluebirds breed in Texas from near sea level to about 1200 m (4000 ft) in a wide variety of habitats, excluding treeless prairies and deep forest interiors (Oberholser 1974). The Oklahoma atlas (Carter and Duggan 2004) mentions open woodlands. In Colorado 85% of the scattered breeding sites were in “lowland” (for Colorado) riparian deciduous woodlands (Kuenning 1998).

Female Eastern Bluebirds build a loosely constructed nest of grasses and forbs in 4-5 days in natural tree cavities, abandoned woodpecker holes or birdhouses. The male brings materials. The inside diameter of the cup is about 6 4 x 7.6 cm (2.5 x 3 in) and the cup depth is 7.6 cm (3 in). The female commonly lays 4-5 (range 3-7) glossy, smooth, pale blue to white, unmarked eggs, indistinguishable from those of Western Bluebird (Sialia mexicana) but darker than the eggs of Mountain Bluebird (Sialia currucoides). The female lays an egg each day and begins incubation after laying the next-to-last egg. Young birds hatch after 11-19 (generally 14) days of incubation and, leave the nest about 19 days after hatching. They stay near cover for 7-10 days and remain in family groups for as long as 3 weeks. Pairs usually raise 2, sometimes 3 broods per year. Helpers at nests are rare as is brood parasitism. Extra-pair copulation occurs. In one study 20% of young had a different father than the male of the pair. (Harrison 1979, Gowaty, and Plissner 1998).

STATUS. Lockwood and Freeman (2004) describe Eastern Bluebirds as uncommon to locally common summer residents of the eastern half of Texas and common in the Panhandle in the Canadian River drainage. The pattern of blocks with breeding evidence on the TBBA map is generally similar to that of. Texas counties with breeding or simmer records on the map in Oberholser (1974). BBS data from 1980-2007 derived from 99 routes provide a statistically significant annual population change of +1.5% similar to the continent-wide change of +2.3% from 2009 routes (Sauer et al. 2008). These results suggest the future of Eastern Bluebirds in Texas is reasonably secure for the foreseeable future.

Text by Robert C. Tweit (2009)

Literature cited

Carter W.. A. and M. D. Duggan. 2004. Eastern Bluebird (Sialia sialis). In Oklahoma breeding bird atlas, pp. 326-327 (D. L. Reinking, ed.). University of Oklahoma Press, Norman.

Corman. Tl E. 2005. Eastern Bluebird (Sialia sialis). In Arizona breeding bird atlas. pp. 428-429 (T. E. Corman and C. Wise-Gervais, eds.). University of New Mexico Press, Albuquerque.

Gowaty, P. A. and J. H. Plissner. 1998. Eastern Bluebird (Sialia sialis), The Birds of North America Online (A. Poole, Ed.). Cornell Lab of Ornithology; Ithaca, NY. Retrieved from: http://bna.birds.cornell.edu/bna/species/381

Harrison, H. H. 1979. A field guide to western birds’ nests. Houghton Mifflin, Boston, MA.

Howell, S. N. G. and S. Webb. 1995. A guide to the birds of Mexico and northern Central America. Oxford University Press, New York.

Kuenning, R. R. 1998. Eastern Bluebird (Sialia sialis). In Colorado breeding bird atlas, pp. 382-383 (H. E. Kingery, ed.). Colorado Bird Atlas Partnership, Denver.

Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.

Oberholser, H. C. 1974. The bird life of Texas. University of Texas Press, Austin.

Sauer, J. R., J. E. Hines, and J. Fallon. 2007. The North American breeding bird survey, results and analysis 1966-2006. Version 7.23.2007. USGS Patuxent Wildlife Research Center, Laurel MD < http://www.mbr-pwrc.usgs.gov/bbs>