The tricolored blackbird (Agelaius tricolor) is a passerine bird of the family Icteridae. Its range is limited to the coastal areas of the Pacific coast of North America, from Northern California in the U.S. (with occasional strays into Oregon), to upper Baja California in Mexico.
This highly social and gregarious bird forms the largest colonies of any North American landbird, with a single breeding colony often consisting of tens of thousands of birds.
The common name is taken from the male bird's distinctive white stripes underneath their red shoulder patches, or "epaulets", which are visible when the bird is flying or displaying.
Despite the similar names, this bird is not related to the Old World common blackbird, which is a thrush (Turdidae).
The species' call sounds slightly more nasal than that of the red-wing's - a nasal kip and a sharp check. The male's song is a garbled on-ke-kaaangh. The bird migrates south during the colder seasons to Mexico and back to northern California during the warmer seasons.
Taxonomy
The tricolored blackbird does not have any officially recognized subspecies, although there is a population in southern California that may require genetic evaluation.
Distribution
The tricolored blackbird nests in colonies, but scholars disagree on whether the costs outweigh the benefits of these breeding habits. Nonetheless, nesting in colonies makes the tricolor susceptible to environmental changes. Although the tricolor has been able to adapt to some of the landscape changes, habitat loss played a major role in the reduction of its population.
The tricolor originally could be found in the marshes of California, nesting in wetland cattails and bulrushes. Scholars have noted a reduction in freshwater marshes as breeding grounds for the tricolored blackbird. Largely, this is due to human activity, and it’s estimated that between the 1930s and 1980s alone, over 95% of wetlands were disappeared. Also in this period, the observed tricolor population saw an 89% reduction, while the average colony size saw a 63% reduction. Altogether, the tricolor population dropped from several million to only a few hundred thousand during the twentieth century. Nevertheless, the tricolor was able to adapt in response to these severe landscape reductions. It began to use both native and non-native vegetation as well as agricultural fields as their breeding and foraging grounds.
In the 1930s, over 93% of the tricolor’s colonies were nested in freshwater marshes, but by the early twenty-first century, only 35% of colonies could be found in wetlands. In 2008, over a fourth of colonies were using non-native vegetation to nest, most notably Himalayan blackberry brambles. Although population decline was a consequence of agricultural intensification over the twentieth century, the birds were able to use these environmental changes to their advantage. The 2008 tricolored blackbird census found that nearly half of the total population nested in colonies inside of the grain fields of dairy farms.
As the twentieth century progressed, the tricolor began to increase in concentration within certain colonies. Specifically, in 2000, 59% birds were housed in one of California’s ten largest colonies, and this number increased to 81% by 2011. Mega-colonies of the tricolor have begun to form in the San Joaquin Valley’s numerous agricultural fields. Although the tricolor population consistently decreased during the twentieth century and into the twenty-first century, the population nested in San Joaquin Valley grew exponentially during this time. The number of tricolors in California’s San Joaquin Valley in 1994 was 230% of what it was in 1937. By 2008, over 86% of California’s population were located here.