A mysterious oil spill off the West Marin coast has killed 220 sea birds this week and prompted an intensive effort by state and federal authorities to protect wildlife in the Point Reyes National Seashore and Gulf of the Farallones National Marine Sanctuary.

Although park officials characterized the spill as minor, a full-scale cleanup and rescue effort with 100 officials and volunteers was mounted immediately after the oil was detected Sunday.

By midweek, 78 sea birds had been cleaned and treated and at least 200 more oiled birds had been sighted but not captured.

Among the birds seen spotted with oil were one brown pelican, an endangered species, and about 10 snowy plovers, a threatened species, said park ranger Carlin Finke.

Furthermore, about 40 cubic yards of contaminated kelp, driftwood, and debris had been removed from the park's beaches, but a few tar balls continued to wash ashore Wednesday in Drake's Bay.

Rangers added they expect to find more dead birds over the next few days.

"We're making good progress," said US Coast Guard Captain Harlan Henderson, a joint commander of the cleanup effort, which includes state Fish and Game wardens, park rangers, private contractors, and volunteers from several local wildlife centers.

Capt. Henderson said Tuesday that the areas most affected by the spill were Limantour Beach, Drake's Beach, and Drake's Estero. All the beaches within the national seashore remained open throughout the week.

Golfball-size tar balls first started appearing on Drake's Beach Sunday morning, followed by scores of dead and dying murres, grebes, pelicans and snowy plovers stained with black oil. Rangers promptly notified the Coast Guard of the situation, said John Dell'Osso, the park's chief of interpretation.

After a brief investigation, the Coast Guard dispatched a helicopter to search the ocean for any signs of an oil slick and tapped into the federal Oil Spill Liability Trust Fund to pay for the multi-agency response.

Wardens from the Fish and Game department's Oil Spill Prevention and Response unit arrived on Monday to begin combing the shoreline for injured birds, while rangers and volunteers took surveys of affected wildlife and assessed the damage.

Throughout Tuesday, contractors with hazardous-material training removed oily debris from the shore. The collaborative effort continued until stormy weather approached at nightfall.

"The storm may help clear things up, or it may bring more tar balls through," Capt. Henderson said Tuesday. "We want to get as much oil as we can before the weather changes on us."

By Wednesday afternoon, however, very little contaminated debris remained on the beaches and the number of recovered birds was slowly dwindling.

The source of the oil spill remains unknown and is under investigation, ranger Finke said.

Samples of the oil were taken to a Coast Guard laboratory in Groton, Connecticut and a state lab in Sacramento for testing and identification, said Fish and Game warden Helen Kevo, another joint commander of the cleanup.

Capt. Henderson told The Light that initial tests would reveal whether the oil is crude or refined. Then it would be "fingerprinted" to see if it matches the oil from previous spills, passing ships, or known shipwrecks.

Despite several flights over the area by Coast Guard helicopters, Capt. Henderson said no oil slick was ever sighted.

Oily birds were collected throughout the week and taken to a mobile veterinary lab at National Seashore headquarters, then to the International Bird Rescue Research Center in Berkeley for rehabilitation.

One of the Fish and Game wardens, Tim Williamson, said the sea birds were being collected on the beaches, which is a sure sign they are in trouble. "They're never on shore unless something's wrong," he said.

At the mobile lab, Dr. Mike Ziccardi assessed the physical condition of oiled birds, took blood samples, and rehydrated them with an electrolyte fluid to neutralize the toxic affects of ingesting petroleum.

"They're pretty heavily oiled and they're fairly thin, which makes it difficult to rehabilitate them. But in general they're pretty bright and alert," Ziccardi said.

Ziccardi said the birds' light body weight could be attributed to the winter season, and park ranger Finke noted that rescuers were having difficulty determining whether some of the birds died of natural causes and were then covered in oil.

Besides the birds, about 11 elephant seals were seen in the vicinity of Chimney Rock with oil on no more than two percent of their body, Finke said.

A biologist with the national seashore, Dr. Sarah Allen, said those seals would clean themselves by rolling in the sand. She added that a colony of 100 harbor seals in Drake's Estero were not in any danger, either.

"They're hauling in and out of the estero, but there's very little oil in the estero," she said, noting that if it were breeding season some of the pups might have been at risk of ingesting oil from their mother's fur.

Because the National Seashore provides sanctuary to so many marine creatures, park superintendent Don Neubacher said the overwhelming response to a relatively minor spill was entirely appropriate.

"We can't make a mistake," he said. "We have to do it right. Every effort we make is worth it."

Neubacher said the cumulative effects of minor spills could prove devastating if they were left unattended, especially for threatened and endangered species.

He added that this collaborative cleanup provides valuable training for more catastrophic spills.