BIG SUR, Calif. — Four years ago, in a musky, leaf-lined cavity halfway up a 200-foot redwood tree here, two California condors made the region’s first known nesting attempt in more than a century.
Joe Burnett, a senior wildlife biologist with the Ventana Wildlife Society and the lead biologist for the Central California condor recovery program, who had been monitoring the condor pair, was delighted with this promising development in the continuing effort to save the nation’s largest bird from extinction. When this first breeding attempt proved unsuccessful, Mr. Burnett attributed it to the young birds’ inexperience. But when he climbed the giant tree to examine the abandoned nest, he was stunned at what he uncovered: the first evidence of a potentially significant new hurdle for the condor program.
“The eggshell fragments we found appeared abnormally thin,” Mr. Burnett said. “They were so thin that we had to run tests to confirm that it was a condor egg.” The fragments reminded him of the thin-shelled eggs from birds like brown pelicans and peregrine falcons, which had been devastated by DDT but are now on the rebound.
The discovery raised a disturbing question: could DDT — the deadly pesticide that has been banned in the United States since 1972 — produce condor reproductive problems nearly four decades later?
To find out, the Ventana Wildlife Society, which manages the Central California condor releases, has collected as many subsequent wild-laid eggs as possible. The handful of Big Sur breeding pairs lay a single egg once every other year. Ventana biologists brave the region’s trackless terrain to exchange a wild-laid egg with one from the zoo-based captive-breeding program. The unsuspecting condor pair then hatches the substitute egg as if it is their own.
In addition, Ventana biologists began to look for possible sources of DDT. Condors are carrion eaters, and in recent years the Big Sur birds have turned to what was historically a major food source: marine mammals. Mr. Burnett now suspects that animals like California sea lions may present a hidden danger to condors. Even today, sea lion blubber contains high levels of DDE, a toxic metabolic breakdown product of DDT.
Ventana biologists have been comparing the thickness of the eggshells recovered from the Big Sur birds with those produced by the Southern California condor flock that lives many miles from the coast. The Southern California birds do not feed on marine mammals, and their eggs are normal. Mr. Burnett says that preliminary results from Ventana’s study suggest that the Big Sur eggs are “substantially thinner” than those from the inland birds, and that early indicators point to DDT as the principal cause of the thinning.
Although no known source of DDT exists near Big Sur, a large DDT hot spot in the marine sediments off the Southern California coast called the Palos Verdes Shelf has attracted Mr. Burnett’s attention because it is near a breeding ground for California sea lions that eat the area’s fish. The sea lions then migrate up the coast. Hundreds of these sea lions use a rocky beach near Big Sur as a stopping point on the trip north. In recent years, this sea lion “haul-out” has become a favorite feeding spot for the Big Sur condors.
The DDT that pollutes the Palos Verdes Shelf originated half a century ago with the Montrose Chemical Corporation. At the time, Montrose was the world’s largest producer of what was once hailed as a “miracle pesticide.” According to Carmen White, the Environmental Protection Agency’s remedial project manager for the site, in the 1950s and ’60s Montrose discharged its untreated DDT waste directly into the Los Angeles County Sanitation District’s sewer system. An estimated 1,700 tons of DDT settled onto the seabed, where it continues to contaminate Pacific Coast waters. The E.P.A. has declared the area a Superfund site, and Ms. White is coordinating a plan to cover the most contaminated parts with a cap of sand and silt in 2012.
According to David Witting, a fishery biologist for the National Oceanic and Atmospheric Administration, diet determines how DDT affects various species. By 1971, when local officials forced Montrose to stop its discharge, Dr. Witting said brown pelicans and other surface-feeding birds had been hit hard. The pelicans were feeding on small, DDT-contaminated fish that picked up the pesticide as it drifted to the surface near the sewer outfall.
Once Montrose stopped discharging DDT into the sewer, that contamination source disappeared. “Brown pelicans rebounded fairly quickly after the dumping stopped,” Dr. Witting said.
James Haas, the environmental contaminants program coordinator for the Pacific Southwest region of the United States Fish and Wildlife Service, noted that other birds in the region that feed higher on the food chain, like bald eagles, continue to suffer from DDT-induced eggshell thinning.
Concerns about condors and DDT have prompted the Fish and Wildlife Service to initiate a new one-year project to study how marine mammals might be carrying Montrose DDT up the California coast. The main investigator, Myra Finkelstein at the University of California, Santa Cruz, is also leading a four-year study to investigate risk factors and management strategies to ensure the condor’s long-term sustainability. This includes not only DDT but also poisoning that comes from ingesting lead-bullet fragments found in hunter-shot game. Lead poisoning was a major factor in the bird’s brush with extinction and remains the primary danger today to released condors.
Because of the lead poisoning problem, in 2008 California enacted legislation requiring hunters in condor country to use ammunition without lead.
Despite lead poisoning and the emerging DDT challenge, Mr. Burnett remains optimistic. He is hopeful that taking steps like capping the DDT-contaminated Montrose marine sediments as well as continuing research will provide solutions. He notes that in 1982 the population of California condors had been reduced to 22 birds. Although problems remain, bringing back the condor has been a conservation success story. There are now 380 California condors in the world, with about half of these titans of the sky flying free in the Western United States.
“There is a light at the end of the tunnel,” Mr. Burnett said. “We just don’t know how far out that light is.”
By JOHN MOIR
http://www.nytimes.com/2010/11/16/science/16condors.html?_r=2
