The gregarious Tricolored blackbird is one of North America's most intensely colonial breeders, forming dense, non-territorial, noisy colonies. A highly synchronized nesting system exploits secure nesting locations and rich food supplies that change from year to year.
In Oregon, breeding colonies are scattered and intermittent at specific locations, though sites used during consecutive years may be in the same general area. The Tricolored blackbird breeds most consistently in Klamath and Jackson Counties. Small colonies and summering residents have been found in the Willamette Valley; during fall and winter they are rare. Most retreat south to California in winter, while some remain in Oregon, mainly in the Rogue Valley and Klamath Basin. Oregon breeding colonies occur in hardstem bulrush, cattail, nettles, willows, and Himalayan blackberries. Breeding colonies are conspicuous because of the high bird density and continuous loud raspy calls.
The male is entirely black, with deep red shoulder patches bordered by white on the wing. The female is blackish brown above, streaked only on the breast, throat, and supercilium.