Plunge of tricolored blackbird population persists in the state, Sacramento Valley

eortiz@sacbee.comJune 19, 2014 

Blackbird Decline

Bob Meese releases a banded tricolored blackbird this month. A new count puts the species at 145,000 in the state, down from millions.

<137>SYLVIA WRIGHT<137><137><252><137> — UC Davis

A recently completed inventory of tricolored blackbirds has found a steep drop in the birds’ spiraling population statewide, with scientists worrying that this year’s drought will lessen future populations.

The steep drop – a 44 percent population plunge since 2011 – was found in a comprehensive survey led by UC Davis, Audubon California and state and national wildlife agencies.

“The tricolored blackbird population is not a stable one. It is rapidly declining,” said Bob Meese, avain ecologist with the UC Davis Department of Environmental Science and Policy.

Declines are being seen throughout the San Joaquin and Sacramento valleys, and as far south as Riverside County. This spring a 143-member team conducted the statewide survey and found only 145,000 tricolored blackbirds. In 2011, the last time the survey was conducted, 260,000 birds were counted.

The low population numbers are a stark contrast to the tricoloreds’ robust presence in California historically. As many as 3 million tricolored blackbirds darkened the state’s skies and farmlands in 1937.

The fear is that declines could lead to the bird becoming endangered and eventually suffering the fate of two colonial bird species, the passenger pigeon and the Carolina parakeet. Both are now extinct.

The reproduction declines were starkest in Colusa and Glenn counties, where no birds were found in areas where they were once plentiful. Kern, Merced and Fresno, where only six tricoloreds were found, also saw steeply plummeting populations. No birds were observed in Kings, Santa Clara and Sonoma counties.

Many mistake the red-winged blackbird for the tricolored. The latter is distinguished by the red feathers in its shoulder patch, with a bright white stripe.

Unlike the red-winged blackbird, the tricolored tends to stay close to home when hunting for insects. In most cases, it will not venture farther than 3 miles from its nesting area.

In the Sacramento Valley, the tricolored’s population drops are attributed to a loss of wetlands due to drought and the establishment of large farms that use pesticides, Meese said. The birds feed on caterpillars, beetles and grasshoppers – the type of insects that farmers seek to control with pesticides.

Urban development is also a factor.

This year’s survey does not adequately reflect how much the current drought is affecting the birds, Meese said, noting that subsequent surveys will measure the full effect. But he expects the drought to lower the tricolored blackbird population.

One effect is that the drought will likely force the birds to breed once instead of twice per year, said Meese. “They may not be able to bring themselves to reproduce a second time. They just will not have enough insects to eat. That could be drought-related,” he said.

The drought has already caused Sacramento Valley rice farmers to fallow thousands of acres of rice. Those fields likely would have served as wetlands for birds and the water as a source of insects that the blackbirds like to feed on.

“There have been a lot of birds that have left areas that are normally kept wet,” Meese said.

The absence of the birds has not gone unnoticed by area farmers. “I haven’t seen the populations of the birds as much as I used to,” said Glenn County rice and olive farmer Dan Kennedy.

Kennedy took note of the birds since they had a habit of feeding on his rice crop. “They’d come in by the thousands and strip the heads right off,” he said.

The importance of wetlands to tricolored blackbirds is underscored by the fact that the population has not declined as much in the central Sierra foothills, said Meese.

“There has been some evidence that the grasshopper population responded to the late storms that hit there in March and April,” he said. The grasshopper is one of the preferred foods of the tricolored blackbird.

The only Central Valley site where the survey found a healthy population of tricolored blackbirds was at private ranch in Yuba County.

Meese said that 15 percent of the state’s tricolored blackbird population was found on the ranch, whose location and owner he chose not to disclose. That ranch has irrigation water applied to its pastureland because of a very high water table, he said.

“I suspect the big colony is the result of this irrigation application,” said Meese.

“And the concern among tricolor biologists is that predators are now having a proportionally much greater impact on the tricolored blackbird species.”

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

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