FRESNO, Calif. - A blackbird species found mostly in the Central Valley of California has experienced a major decline in its population during the past several years due in part to farming practices, researchers say.

The tricolored blackbird now numbers about 145,000 in the state, down from millions less than a century ago, a survey released Wednesday shows.

Robert Meese, a University of California, Davis, researcher who led the study, said Californians must act to reverse the decline.

"It's our responsibility because it's our bird," he said. "We're going to have to take an all-hands-on-deck approach."

Meese conducted the survey with the U.S. Fish and Wildlife Service, California Department of Fish and Wildlife and Audubon California.

It found the tricolored blackbird population has decreased 64 percent since 2008. The decline is blamed at least in part on the harvesting of feed crops on dairy farms where the bird has come to nest.

The Central Valley had been a stronghold for the birds, but the survey found that their numbers plummeted in Kern and Merced counties, and only six were found in Fresno County. No birds were found in Kings County, Meese said.

Tricolored blackbirds historically nested in wetlands but with those areas increasingly drying up, bird colonies moved into fields where a wheat-rye hybrid is grown and used to feed dairy cattle, researchers say. However, those fields are often harvested before the young birds leave the nest.

Meese is working with land owners in Yolo and Yuba counties to provide habitat for the birds. He is also working with the University of California, Merced, to provide a nesting reserve at the Central California campus.