This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Populations of California's already endangered tricolored blackbirds (Agelaius tricolor) have fallen by 44 percent since 2011 and 64 percent since 2008, according to a survey coordinated by the University of California, Davis. The state is now home to just 145,000 of these birds, which live almost exclusively in California. Eighty years ago the population numbered in the millions.
This new count comes from a statewide survey conducted this past April in which 143 volunteers inspected more than 800 sites in 41 California counties. Some counties, such as Amador and Sacramento, had somewhat larger numbers of blackbirds than in a previous survey in 2011 but most didn't fare so well. Fresno County only had six blackbirds. Kings, Santa Clara and Sonoma counties had none.
The biggest decline was seen in California's Central Valley, which has also historically been the birds' biggest breeding area. During the 2011 survey 89 percent of breeding tricolored blackbirds were observed in the valley. This year's survey found that the birds are quickly disappearing in that region, mostly because their former wetlands habitat has been converted into fields of a wheat–rye hybrid called triticale, which is used to feed cattle in California's "dairy belt." According to U.C. Davis, the birds still nest there but the triticale fields are often harvested before young birds have left their nests, resulting in thousands of deaths. Triticale loses some of its nutritional value if it grows for too long, so many farmers feel they can't delay harvesting the grain until the birds leave their fields.
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Although they are legally protected under the Migratory Bird Treaty Act, the tricolored blackbirds also often die in farmers' gun sights when they are mistaken for red-winged blackbirds (A. phoeniceus). Red-wings are also protected under the treaty but there's a special exemption in the law that allows farmers to shoot them if the birds are eating up valuable rice fields.
In addition to documenting the declines, the survey offers critical information that can be used to conserve the species. "This survey helps us not only get an accurate population estimate, it also tells us where we can focus our recovery efforts," said Monica Iglecia, a project manager with Audubon California, one of the organizations which assisted with the survey.
Those efforts will need to start quickly, said U.C. Davis staff researcher Robert Meese, who ran the census. "The reality is we have to get on the ground and start taking immediate action. If that process doesn’t get started right away, we’re going to lose these birds."
Tricolored blackbirds are not currently protected under the Endangered Species Act (ESA), although they have been considered a candidate for protection since 1982. BirdLife International classified the species as endangered in 2006.
Photo: Robert Meese preparing to release a tricolored blackbird. Photo by Sylvia Wright, courtesy of U.C. Davis
