The Altamont wind farms saw an apparent increase in bird deaths last year in spite of efforts to reduce the bird kills, according to a new report.

Bird-carcass surveys at about half of the nearly 5,000 Altamont wind turbines found a striking jump in deaths among many species in the year ending last September over the previous year.

The report - produced by a consortium of consultants who are coordinated by Brian Latta of the UC Santa Cruz Predatory Bird Research Group - cautioned that the results are preliminary and that the cause of the increase in bird deaths is not known.

The number of bird deaths does not appear to be decreasing despite measures to reduce the deaths, the report said. Those efforts include shutting down all the turbines for two months in the winter and a not-yet fully-accomplished process of relocating or permanently shutting down the windmills suspected of causing the most deaths.

The report said further study is needed to determine whether the results could be explained by seasonal variations, such as an increase in the number of birds in the Altamont Pass.

The report is part of an ongoing program overseen by Alameda County to reduce Altamont bird deaths.

The county's supervision is being coordinated with a court settlement in which most of the wind companies agreed to reduce deaths of four targeted raptor species by 50 percent within three years from the date of the settlement. The different parties in the court settlement disagree on the exact date, variously saying the settlement occurred sometime between November 2006 and February 2007.

The number of actual dead birds found among the four targeted species - burrowing owl, American kestrel, red-tailed hawk and golden eagle - increased nearly 90 percent from 2005-06 to 2006-07, the report found. The total number of dead birds counted in the 2-year period includes 229 red-tailed hawks, 150 burrowing owls, 56 American kestrels and 49 golden eagles, the report says.

The annual deaths of the four species combined at all the windmills during the study period are estimated to range between 1,839 and 2,906. Latta said the estimates are subject to revision upon further analysis.

Elizabeth Murdock, executive director of the Golden Gate Audubon Society, one of the plaintiffs in the lawsuit behind the legal settlement, said, "It's distressing that the report seems to indicate that the mortality hasn't gone down."

Steven Stengel, spokesman for the largest wind operator in the Altamont, FPL Energy, said the company needs to review the report further before commenting on it.

"We need to reduce the number of collisions while at the same time allow the turbine operators to continue to operate the turbines so that California can enjoy the emissions-free wind power generated by these facilities," Stengel said.

The windmills are shut down for two months during the low-wind season each winter as part of the effort to curb bird kills. Nearly 100 of the most dangerous turbines have been shut down or removed, and the parties are negotiating over recommendations by a county-appointed scientists' panel to remove more than 300 additional ones. A small blade-painting test was conducted in the past on some turbines, and one wind company has proposed a larger test.

The Golden Gate Audubon Society contends the companies have failed to meet conditions of the settlement and invoked a mediation clause to resolve several issues. The first mediation session was held Jan. 18, and a second is scheduled for Feb. 8.

Get involved

A public workshop on the Altamont wind farms and bird-death problem will be held Feb. 12 at the Waterfront Plaza Hotel, 10 Washington St., in Oakland's Jack London Square.

The meeting is tentatively scheduled to begin at 1 p.m. Those interested in attending are urged to check the final agenda and meeting documents at links.sfgate.com/ZCHV.

Click here to read the bird death report.