A practical guide to bird watching in Sonoma County, California
(Unless otherwise indicated, all phone numbers are in the 707 area code)
Much maligned for its unusual strategy of forgoing nest-building and parasitizing the nests of other birds at the expense of host chicks, but Brown-headed Cowbird has become an enlarged threat to other native birds through no fault of its own. It was once confined mostly to the central United States, where it was associated with bison. It has spread widely because of human activity: Clearing forests has vastly increased the edge habitat this bird favors. Today, Brown-headed Cowbird is seen more with domestic cows than bison. In Sonoma County, found more often in summer than in winter, but present year-round. In the winter months, tends to associate with other blackbirds and with European Starling (Sturnus vulgaris), sometimes in very large flocks. Can be found in open edge habitats in most of the county near deciduous woods and especially around farmland, where it hangs out near cattle pens. According to Birds of Sonoma County, reports show Brown-headed Cowbird was considered unusual here in the late 1920s but common by the 1960s--making it a fairly recent arrival.
The male Brown-headed Cowbird (pictured above) has a bluish-black body and contrasting bronzy brown head, which makes it easy to pick out in good light. Backlit or in large mixed flocks, it can be harder to identify. Compared with other blackbirds and allies, Brown-headed Cowbird has a comparatively short, finch-like bill and a shorter tail (compare Brewer's Blackbird (Euphagus cyanocephalus), Red-winged Blackbird (Agelaius phoenicius), and European Starling). The very short-tailed Starling is distinguished by its yellow bill and extensive streaking and spotting. Female Brown-headed Cowbirds are paler than the females of the other blackbird species and more brownish. Again, the bill is shorter, wider, and more finch-like. Immature birds (photos below) have some streaking, but the bill should distinguish this bird from juveniles of other blackbird species. Scroll down to see photos of a young cowbird being fed by its host parent, a Hutton’s Vireo.
Further reading:
Bolander and Parmeter, Birds of Sonoma County California, rev. ed., 2000, p. 122
Brinkley, National Wildlife Federation Field Guide to Birds of North America, 2007, p. 419
Burridge, ed., Sonoma County Breeding Bird Atlas, 1995, p. 173
Dunn and Alderfer, eds., National Geographic Field Guide to the Birds of North America, 5th ed., 2006, p. 448
Dunn and Alderfer, eds., National Geographic Field Guide to the Birds of North America, 6th ed., 2011, p. 508
Dunne, Pete Dunne’s Essential Field Guide Companion, 2006, pp. 655-656
Ehrlich, Dobkin, and Wheye, The Birder's Handbook, paperback edition, 1988, p. 616
Fix and Bezener, Birds of Northern California, 2000, p. 352
Kaufman, Field Guide to Birds of North America, 2000, p. 338
Kaufman, Field Guide to Advanced Birding, 2011, pp. 99, 102
Parmeter and Wight, Birds of Sonoma County California, Update (2000-2010), 2012, p. 73
Peterson, Birds of Eastern and Central North America, 5th ed., 2002, p. 314
Peterson, Field Guide to Birds of Western North America, 4th ed., 2010, p. 356
Peterson, Western Birds, 3rd ed., 1990, p. 310
Sibley, Field Guide to Birds of Western North America,1st ed., 2003, p. 444
Stokes, Stokes Field Guide to the Birds of North America, 1st ed., 2010, p. 728
Vuilleumier, American Museum of Natural History, Birds of North America: Western Region, 2011, p. 375
Voice: Cornell Lab of Ornithology: All About Birds--Brown-headed Cowbird
© Colin Talcroft, 2009-2020
Unless noted, all photos by the author. If you would like to use one of my images, please ask for permission for non-commercial use with proper credit or commercial use with proper compensation.
For comparison: Male Brewer's Blackbird--Note purplish head, pale eye, pointed bill
Female Brown-headed Cowbird--Note pale brownish color; lack of striping (relative to female Red-winged Blackbird); shorter, heavier bill relative to other blackbirds
For comparison: Female Brewer's Blackbird
Note greyer color with hints of blue; sharper, longer bill Lake Ralphine, February 25, 2012
Juvenile Brown-headed Cowbird--Note pale brownish color; shorter, heavier bill relative to other blackbirds
July 14, 2012, Shollenberger Park, Petaluma
1990-2013 Sonoma County data. Graph provided by eBird (www.ebird.org), generated May 30, 2013
EBird reported occurrence in Sonoma County
Brown-headed Cowbird
Molothrus ater
Brown-headed Cowbird, Marin Headlands (Marin County), May 13, 2011
Young Brown-headed Cowbird with its host parent, a Hutton’s Vireo.
Spring Lake, Santa Rosa, July 5, 2020
Young Brown-headed Cowbird with its host parent, a Hutton’s Vireo.
Spring Lake, Santa Rosa, July 5, 2020
