The Introduction Article is just the first of 11 articles in each species account that provide life history information for the species. The remaining articles provide detailed information regarding distribution, migration, habitat, diet, sounds, behavior, breeding, current population status and conservation. Each species account also includes a multimedia section that displays the latest photos, audio selections and videos from Macaulay Library’s extensive galleries. Written and continually updated by acknowledged experts on each species, Birds of North America accounts include a comprehensive bibliography of published research on the species.
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This map depicts the seasonally-averaged estimated relative abundance, defined as the expected count on a one-hour, one kilometer eBird Traveling Count conducted at the ideal time of day for detection of that species in a region.
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Adult female Western Bluebird, Baja California, December
Female Western Bluebird, presumably of the subspecies occidentalis. Guadalupe Canyon, Baja California, Mexico; 31 Dec 2005.; photographer Brian L. Sullivan
Adult male Western Bluebird, Baja California, December
Male Western Bluebird, presumably subspecies occidentalis. Guadalupe Canyon, Baja California, Mexico; 31 Dec 2005.; photographer Brian L. Sullivan
Western Bluebirds are small thrushes that breed throughout much of the western United States, Mexico, and southwestern Canada. Males have brilliant blue plumage on their heads, wings, and tails, rust colored breasts, and, frequently, chestnut back patches; females are duller and have more brown and gray in their feathers. Insectivorous during the warmer months, individuals forage primarily on berries and fruits through the winter; wintering individuals are especially abundant in years and in areas when mistletoe (Phoradendron spp.) and juniper (Juniperus spp.) berry crops are plentiful.
Western Bluebirds are socially monogamous. Both parents usually care for young, but they also seek matings outside the pair bond, with the result that offspring are not always related to the attendant male. Helpers at the nest occur in some populations and are frequently adult male relatives, often putative sons of the resident pair, or juveniles from earlier broods.
Western Bluebirds can usually be found in open, parklike forests, edge habitats, burned areas and where moderate amounts of logging have occurred, provided a sufficient number of larger trees and snags remain to provide nest sites and perches. Unlike Eastern (Sialia sialis) and Mountain (Sialia currucoides) bluebirds, Western Bluebirds do not favor large, open meadows. Clear-cutting, snag removal, fire suppression, and any changes in land use that cause open forest and edge habitat to be diminished adversely affect Western Bluebird populations.
Apparent declines in numbers of this species in the Pacific Northwest and British Columbia, especially in regions west of the Cascade Range, have generated concern. In response, bluebird enthusiasts in Washington, Oregon, and British Columbia have established trails of nest boxes in an effort to reestablish local breeding populations.
Systematic studies of Western Bluebird ecology and behavior are limited. Information on some topics is anecdotal or missing altogether. Key studies include: breeding biology and phenology in Washington (
Herlugson, C. J. (1980). Biology of sympatric populations of Western and Mountain bluebirds. Phd Thesis, Washington State Univ., Pullman.
Herlugson 1980); mating behavior in California (
Dickinson, J. L. and M. L. Leonard. (1996). Mate attendance and copulatory behavior in Western Bluebirds: evidence of mate guarding. Animal Behaviour 52:981-992.
Dickinson and Leonard 1996,
Dickinson, J. L. (1997). Male detention affects extra-pair copulation frequency and pair behavior in Western Bluebirds. Animal Behaviour 53:561-571.
Dickinson 1997,
Dickinson, J. L. and J. J. Akre. (1998). Extrapair paternity, inclusive fitness, and within-group benefits of helping in Western Bluebirds. Molecular Ecology 7:95-105.
Dickinson and Akre 1998,
Dickinson, J. L., K. Kraaijeveld and F. Smit-Kraaijeveld. (2000). Specialized extrapair mating display in Western Bluebirds. Auk 117 (4):1078-1080.
Dickinson et al. 2000,
Dickinson, J. L. (2001). Extrapair copulations in western bluebirds (Sialia mexicana): female receptivity favors older males. Behavioral Ecology and Sociobiology 50 (5):423-429.
Dickinson 2001); parental behavior in Arizona and California (
With, K. A. and R. P. Balda. (1990). Intersexual variation and factors affecting parental care in Western Bluebirds: a comparison of nestling and fledgling periods. Canadian Journal of Zoology 68:733-742.
With and Balda 1990,
Leonard, M. L., K. L. Teather, A. G. Horn, W. D. Koenig and J. L. Dickinson. (1994). Provisioning in Western Bluebirds is not related to offspring sex. Behavioral Ecology 5:455-459.
Leonard et al. 1994,
Leonard, M. L., J. L. Dickinson, A. G. Horn and W. Koenig. (1995). An experimental test of offspring recognition in Western Bluebirds. Auk 112:1062-1064.
Leonard et al. 1995,
Dickinson, J. L. and W. W. Weathers. (1999). Replacement males in the western bluebird: opportunity for paternity, chick-feeding rules, and fitness consequences of male parental care. Behavioral Ecology and Sociobiology 45 (3-4):201-209.
Dickinson and Weathers 1999,
Dickinson, J. L. (2003b). Male share of provisioning is not influenced by actual or apparent loss of paternity in western bluebirds. Behavioral Ecology 14 (3):360-366.
Dickinson 2003b); helping behavior in California (
Dickinson, J. L., W. D. Koenig and F. A. Pitelka. (1996). Fitness consequences of helping behavior in the Western Bluebird. Behavioral Ecology 7:168-177.
Dickinson et al. 1996,
Dickinson, J. L. (2004a). A test of the importance of direct and indirect fitness benefits for helping decisions in western bluebirds. Behavioral Ecology 15 (2):233-238.
Dickinson 2004a,
Dickinson, J. L. (2004b). Facultative sex ratio adjustment by western bluebird mothers with stay-at-home helpers-at-the-nest. Animal Behaviour 68:373-380.
Dickinson 2004b); foraging habits in Washington and Arizona (
Pinkowski, B. C. (1979). Foraging ecology and habitat utilization in the genus Sialia. In The Role of Insectivorous Birds in Forest Ecosystems (J. G. Dickson, R. N. Conner, R. R. Fleet, J. C. Kroll and J. A. Jackson, Editors), Academic Press, New York, NY, USA. pp. 165-190.
Pinkowski 1979d,
Herlugson, C. J. (1983b). Hover-foraging by Western Bluebirds. Murrelet 64:58-60.
Herlugson 1983b); habitat selection and use in Arizona (
Szaro, R. (1976). Population densities, habitat selection and foliage use by the birds of selected ponderosa pine forest areas in the Beaver Creek watershed. Phd Thesis, Northern Arizona Univ., Flagstaff.
Szaro 1976,
Cunningham, J. B., R. P. Balda and W. S. Gaud. (1980a). Selection and use of snags by secondary cavity-nesting birds of the ponderosa pine forest. U.S. For. Serv.
Cunningham et al. 1980a,
Brawn, J. D. (1985). Population biology, community structure, and habitat selection of birds in ponderosa pine habitat. Phd Thesis, Northern Arizona Univ., Flagstaff.
Brawn 1985); environmental effects on breeding and feeding ecology in Arizona and New Mexico (
Szaro, R. (1976). Population densities, habitat selection and foliage use by the birds of selected ponderosa pine forest areas in the Beaver Creek watershed. Phd Thesis, Northern Arizona Univ., Flagstaff.
Szaro 1976,
Brawn, J. D. (1991). Environmental effects on variation and covariation in reproductive traits of Western Bluebirds. Oecologia 86:193-201.
Brawn 1991,
Fair, J. M. and O. B. Myers. (2002b). The ecological and physiological costs of lead shot and immunological challenge to developing western bluebirds. Ecotoxicology 11 (3):199-208.
Fair and Myers 2002b,
Germaine, H. L. and S. S. Germaine. (2002). Forest restoration treatment effects on the nesting success of Western Bluebirds (Sialia mexicana). Restoration Ecology 10 (2):362-367.
Germaine and Germaine 2002,
Colestock, K. L. (2006). Landscape scale assessment of contaminant effects on insectivorous birds. Master's Thesis, Utah State Univ., Logan.
Colestock 2006,
Wightman, C. S. and S. S. Germaine. (2006). Forest stand characteristics altered by restoration affect Western Bluebird habitat quality. Restoration Ecology 14 (4):653-661.
Wightman and Germaine 2006); and growth and energetics in California (
Mock, P. J. (1990b). Energetics of growth and reproduction of the Western Bluebird, Sialia mexicana. Phd Thesis, Univ. of California, Los Angeles.
Mock 1990b). More information is needed about Western Bluebird vocalizations, migratory physiology and habits, winter ecology, survivorship and mortality, and dispersal habits. Comparative studies of Western Bluebirds to Eastern and Mountain bluebirds in flexible responses to climate and habitat change may also prove interesting.
Recommended Citation
Guinan, J. A., P. A. Gowaty, and E. K. Eltzroth (2008). Western Bluebird (Sialia mexicana), version 2.0. In The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.510
Data provided by eBird
Western Bluebird
Sialia mexicana
Abundance
This map depicts the seasonally-averaged estimated relative abundance, defined as the expected count on a one-hour, one kilometer eBird Traveling Count conducted at the ideal time of day for detection of that species in a region.
Learn more