Crash In Tricolored Blackbird Population Has Biologists Worried

Tricolored blackbird in Fresno County | Photo: Marcel HOlyoak/Flickr/Creative Commons License

A bird sometimes called "California's passenger pigeon" is in worse trouble than some wildlife advocates suspected. According to a survey by wildlife biologists, the population of tricolored blackbirds has dropped by 44 percent since 2011.

The tricolored blackbird (Agelaius tricolor), a close relative of the far more common red-winged blackbird, once formed huge breeding colonies of hundreds of thousands of birds in wetlands in the Central Valley, and was considered the most common bird in California in the 19th Century. With those habitats mostly gone, the birds now breed mainly in farmers' fields -- which means tens of thousands can be killed by a single ill-timed harvest.

When ReWild reported in April on one such colony of around 50,000 blackbirds threatened by a wheat harvest, we quoted figures for the world's tricolored blackbird population at between 250,000 and 300,000 birds. We were way off. According to the survey, performed by UC Davis biologists with aid from Audubon California, the California Department of Fish and Wildlife, and the U.S. Fish & Wildlife Service, that population now stands at 145,000 individuals, a 44 percent drop from 2011's figure of 260,000.

That earlier story, by the way, had a happy ending for the short term: Audubon California was able to negotiate with the farmer to delay harvest until the breeding birds had moved on.

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That's pretty much it for the good news. According to the survey, the birds' numbers dropped precipitously even in the San Joaquin Valley, which had been the core of their range in recent years. In addition to disruption of breeding colonies by agricultural harvesting, the drought is also thought to have played a role by shrinking the Central Valley's few remaining wetlands even further.

"It's disheartening to witness this bird struggling to survive in California," said Monica Iglecia of Audubon California. "This year's drought reduced the amount of wetland habitat in the spring and summer, which is when Tricolored Blackbirds are nesting and when they need it most. This presents a serious danger for a population this small."

At 801 sites surveyed in 41 counties, only a few sites in Sacramento, Amador, and El Dorado counties didn't show a decline in blackbird numbers. There were no blackbirds at all found in Kings, Santa Clara, or Sonoma counties, and Fresno County sites had a total of six birds.

Even parts of the state that had relatively healthy blackbird populations in 2011, such as Kern and Merced counties, had so many fewer blackbirds surveyed in 2014 that an Audubon California press release described their numbers as having "plummeted."

And those statewide numbers are crucial, because aside from a couple thousand birds that breed in Oregon, and a dozen or so in Washington, Nevada, and Baja California, the California population is the total global population of tricolored blackbirds.

"It's California's blackbird," said survey head Robert Meese of UC Davis. "If we as Californians don't care about the species, we can't rely on any other state to come in and bail us out. It's our responsibility because it's our bird."

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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