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Thursday, Jan. 10, 2008

Dark future is feared for tricolor blackbirds

The Central Valley fixture could be on path to extinction

For tricolor blackbirds that swoop and gather in Central Valley fields, the past breeding season turned unexpectedly into a nearly silent summer.

By the tens of thousands, the birds courted, built nests and waited – then abandoned nests en masse as females failed to produce eggs.

Robert Meese, a UC Davis researcher who tracks the trademark California bird with its blaze of red and white on the wings, hopes biologists are seeing just a temporary setback, fueled by dry weather that depleted a vital supply of insects.

"If this is the beginning of a trend rather than a one-time event we might really be in trouble with the tricolor," said Meese. "The bird is making its last stand, and it's making its last stand primarily in the Central Valley."

Meese, who has tracked tricolors in all seasons, even hearing a field erupt with the odd, mewing cry the males utter only when courting, will discuss the bird's life and perils tonight in Davis.

Most of the world's tricolor blackbirds live in California, and federal and state officials are watching closely: The birds that once filled California skies have been in a decades-long decline, although they are not listed as threatened or endangered.

Instead, it is a bird of "conservation concern," which could face greater peril if steps are not taken to slow its decline, said Michael Green, a bird biologist for the U.S. Fish and Wildlife Service in Portland.

Tricolor blackbirds look a little like red-winged blackbirds, with an added slash of white below the red in males. But tricolors act completely differently, in ways that could be contributing to their hard times.

"They're the most colonial land bird in North America," Green said. They congregate to breed in large flocks that can leave huge numbers of birds imperiled if anything goes wrong at their chosen site.

"It's just an amazing sight; it's a spectacle," Green said.

"In a farmer's 100-acre field you can have 30 percent of the world's population. That's what makes them somewhat vulnerable."

Green is hoping the bird just endured the "bust" period in a "boom-bust" cycle that may be typical for such a colonial bird – although no one is sure yet.

Federal wildlife officials conduct detailed surveys of the tricolor's population only once every three years. It should learn more this year because the next triennial survey is scheduled for April.

The Audubon Society is still looking for experienced bird watchers to help with that survey, particularly in Solano, San Joaquin, Stanislaus, Merced, and Fresno counties, said Graham Chisholm, director of conservation for Audubon California.

Audubon plans to dispatch volunteers to where the bird has been known to congregate, and will ask people to estimate the numbers of any colonies they find.

"What's unusual about the tricolor blackbird," said Chisholm, "is that 95 percent of the tricolor blackbirds in the world occur in California. Our responsibility for its conservation is extraordinarily high."

Well over 1 million birds were once reported in the Sacramento Valley, and in the 1930s 500,000 tricolor blackbirds nested in the area now covered by Lake Natoma, said UC Davis' Meese. They filled the coastal marshes of Southern California.

Now there are an estimated 250,000 to 300,000. They've taken to agricultural sites, scooping fat aquatic beetles out of rice fields and feasting on grains.

Often they nest in triticale, a wheat-rye hybrid grown as livestock feed. Its thick stalks can support a tricolor blackbird's nest, replacing marsh reeds.

The switch to triticale means trouble, though, when a grower is ready to harvest before hatchlings have fledged. A multiagency working group organized to help save the bird is negotiating with growers to protect breeding fields until baby birds have flown.

While adult males and non-breeding females will eat either grain or bugs, female tricolor blackbirds need to switch to insects when they're ready to lay eggs.

The bugs provide amino acids and essential fatty acids needed to produce viable eggs in healthy numbers, Meese said.

He thinks summer of 2007 may have been especially bad for tricolors because an unusually dry winter was followed by a badly timed spring cold snap, decimating insect populations.

"I'm pretty sure it's lack of bugs. I don't suspect pollutants because it's way too widespread," Meese said.

He and colleagues monitored 27 colonies of tricolor blackbirds in the Central Valley in 2007, and only three produced average numbers of young. Two small colonies in the San Diego area apparently reproduced normally, but still face significant threats because of their size, Meese said.

"The bird is in trouble in Southern California, huge trouble," he said, even though it used to be one of the most abundant birds in south state coastal marshes.