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 have some streaking, but the bill should distinguish this bird from juveniles of other blackbird species.

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, 2010, 201, 2012

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