While collecting birds late in his life along the upper Missouri and Yellowstone Rivers in June 1843, John James Audubon took several specimens of a blackbird he believed was new to science. He named it Quiscalus breweri after Thomas Mayo Brewer, a friend who was a Boston physician and ornithologist. The species had been described previously, however, as Psarocolius cyanocephalus in 1829 by Johannes Wagler; the specific name, meaning blue-headed, is therefore retained by ornithologists, while the English name still honors Brewer. From time to time the bird also has been known locally as “Satin Bird” or “Glossy Blackbird.” These colloquial names are rarely used, yet they nicely capture the impression given by sunlit males: their plumage is highlighted by striking violet and blue-green iridescence, punctuated by piercing yellow eyes.
An historically common and conspicuous social species and colonial breeder in open habitats and in farmstead and suburban settings of western North America, Brewer's Blackbird was not recorded nesting east of western Minnesota before 1914. Beginning about then and continuing over the next 4 decades, it undertook a rapid, leap-frog patterned eastward expansion of its breeding range, extending nesting populations approximately 1,200 km at an advancement rate averaging 18 km/year. The pioneering birds took advantage of forest clearing and land conversion to agriculture, and followed linear highway, railroad, and utility corridors to penetrate unfavorable barriers and reach new areas of appropriate breeding habitat. Extension of the species' nesting range also occurred in western Canada, as Brewer's Blackbirds moved 300 km north of their traditional breeding areas to eventually reach southern Mackenzie. Enlargement of the range used by wintering birds occurred concurrently, and now the species is common during winter in the southeastern United States. Today, the Brewer's Blackbird is viewed as a model for understanding avian range expansions promoted by human alterations in habitat.
As this blackbird moved eastward, it became sympatric with the long-entrenched Common Grackle (Quiscalus quiscula), both species showing strong preferences for open habitats and suburban environments. Surprisingly, interactions between the two resulted in the competitive exclusion and displacement of the larger grackles from long-occupied sites in localized rural settings dominated by grassy habitats ( Stepney 1979b ), but not from urban or suburban habitats where the grackles persisted. Interestingly, the relatively recent invasion by Common Grackles of Front Range communities along the base of the Rocky Mountains coincided with the disappearance of Brewer's Blackbirds from the urban and suburban communities they had long utilized in this region, suggesting that Brewer's may be competitively superior in a variety of grassland environments along the Front Range, but that the Common Grackle may be better adapted in city and town situations. This is deserving of focused research.
Because of the ease of its study, its broad ecological plasticity, and its occupancy of environments that can be quite unpredictable over brief as well as long periods, the Brewer's Blackbird has been used as a subject to evaluate model hypotheses related to intriguing questions of behavioral and evolutionary ecology. The research for several Master theses and Ph.D. dissertations ( Mulford 1936 ; Verbeek 1962a ; Horn 1966a ; Stepney Stepney 1971 , Stepney 1979b ; Furrer 1974 ; O'Connor 1976 ; Irwin 1989 ) have explored a variety of such themes, all of which contribute to the account presented here. While the authors of these insightful studies wrote dissertations and published papers addressing their findings as they related specifically to the model hypotheses under examination, many of the underlying life history, ecological, and behavioral observations and data were not presented in the written products, leaving gaps in the published literature on many details of breeding biology, wintering ecology, and behavior of this interesting blackbird—but also leaving rich opportunities for future studies by professional and amateur ornithologists!