SAUSALITO (CBS SF) – 24 seabirds that had been covered in a mysterious goo were returned to the wild on Wednesday in Sausalito.

The birds have undergone expert medical stabilization, cleaning and re-waterproofing since they were discovered covered in a mysterious substance in parts of the East Bay earlier this month.

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International Bird Rescue chose the spot at Fort Baker to release the seabirds.

“We’ve chosen this location because there is a tremendous herring spawn going on here right now,” said Barbara Callahan, Interim Executive Director with International Bird Rescue. “You can see all the gulls and seabirds right off the jetty. There’s about 100,000 other seabirds right here so we know they’re going to be in good company.”

The 24 birds are the first to be released. More than 200 were admitted to the International Bird Rescue’s Fairfield facility since the first birds were found covered in the substance on January 16.

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No new birds have been found to have the mystery goo on them since January 22.

As for exactly what that substance is? Officials still can’t answer that question.

“We’re working collaboratively with the laboratories, public and private, to identify the source,” said Scott Birkey with the California Department of Fish and Wildlife. “A lot of people are putting a lot of hours in. We are actively looking and actively researching and trying to find the source product.”

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Birkey said in his time spent investigating similar incidents, he has never seen anything like this one. More than 200 birds have died in the Bay Area due to the mysterious substance.