WILLIAMS – The use of pesticides and other farming practices are causing a dramatic decline in the population of what was once one of the state’s most populous bird species: the tricolored blackbird.

A recent estimate has pegged the population of the small, dark and swift-moving birds at 260,000. That’s down from 400,000 birds counted in 2008, according to an Audubon California survey.

The tricolored blackbird – with its red shoulder patch and a white bar of feathers on its wing – differs from the more common red-winged blackbird in that it is a species that lives in tight colonies.

“We are, absolutely, concerned about the species because we’ve had a 33 percent decline in their numbers between 2008 and 2011,” said Keiller Kyle, conservation project director for Audubon California.

The declines are being seen throughout the San Joaquin and Sacramento valleys and as far south as Riverside County. The low population numbers are a stark contrast to what was seen in 1937, when it was estimated that as many as 3 million tricolored blackbirds darkened the sky statewide.

With substantially lower populations today, the fear is that if the species is not safeguarded, it could become endangered and swiftly go the way of two colonial bird species – the passenger pigeon and the Carolina parakeet. Both are now extinct.

In the Sacramento Valley, loss of wetlands and the establishment of large farms that use pesticides are deeply curtailing the tricolored blackbird population, Kyle said. The birds feed on caterpillars, beetles and grasshoppers – the type of insects pesticides are designed to control.

The birds demand a lot of insects. Kyle has been studying a colony of 1,000 birds that have recently nested in a bamboo stand inside the Bransford rice farm in Williams.

The size of farms has also been affecting the birds. Large farm concerns, such as rice farms, limit the tricolored blackbird’s food supply because the birds roam only within a 5-mile wide radius from their colony.

“The birds are only able to use the edges of the flooded rice fields and that really limits the area for them to find food,” Kyle said. “Also, the row crops that have been prolific in the valley like alfalfa – a lot of that is being converted over to orchards and vineyards – which means the birds are also losing the open country.”

In the south, the disappearance of forests and wetlands have forced the birds to set up nests in wheat fields.

When farmers harvest the wheat for cattle feed, their tractors tear up the nests with chicks that have yet to fledge, said Robert Meese, avian-ecologist at UC Davis.

Meese said the scarcity of food for the tricolored blackbird in the Sacramento Valley has made it difficult for the birds to reproduce.

“Since 2007 we are seeing that it takes the birds multiple nests to produce a single fledgling,” Meese said. “And that’s simply because the birds are near starvation. In some cases the females are unable to form eggs. They come in and they mate and they build nests and sit for a week, and then they abandon them.”

Meese said that population surveys have found more colonies overall, but that each has fewer birds.

Moreover, only 60 percent of adult tricolored blackbird males survive through the winter. “There are too few young being fledged now to replace the adults that are dying,” he said.

In the Sacramento Valley, the tricolored blackbird population has gone from 37,933 in 2008 to 19,164 birds in 2011.

Meese said that he is expecting populations of the tricolored blackbird to plunge further once a new count of the birds is finalized by next April.

“We need to identify willing landowners to switch from using insecticides to organic or pesticide-free growing,” said Meese.

One solution may be found in a plan currently being implemented by six dairy and wheat farmers in Kern County, the Audubon Society and the National Resources Conservation Service.

In that effort, dairy farmers hold off harvesting their wheat crop to allow tricolored blackbirds to fledge. In turn they have been compensated – at 75 percent of the market rate – for the delay of harvest, said Alan Forkey conservationist with the conservation service.

“Dairy farmers are struggling right now economically and cost of feed is very important so to delay harvest you are losing quality on your feed and delaying planting of your summer crop,” said Paul Sousa, director of environmental services for Western United Dairymen.

It’s estimated the project has saved the lives of 65,000 birds. The six dairy farmers participated voluntarily, Sousa said.

“These six farms that volunteered were the most crucial because they had the largest number of birds on their farms,” he said. “We would like to keep this voluntary and not have these birds listed as endangered.”

In the Sacramento Valley, rice farmer Don Bransford has willingly changed his farm practices to help safeguard the colony of tricolored blackbirds that have recently started to nest in a stand of bamboo on his rice farm.

Bransford said he uses pesticides only sparingly, if at all, and that he flattens levees and leaves islands in flooded rice fields to improve nesting and feeding habitats for the birds. He said he is not getting compensated for changing his farming habits.

“If this improves the bird’s population, then I see it as a win-win for everyone,” he said.

Call The Bee’s Edward Ortiz, (916) 321-1071. Follow him on Twitter @edwardortiz.