Scientists are so far stumped in an ongoing mystery to identify a gooey, rubber-cement-like substance that has killed over 200 seabirds in the San Francisco Bay.

Last month, seabirds — mainly surf scoters, horned grebes, common goldeneyes, and scaups — began coming ashore suffering from hypothermia due to a mysterious goo coating their wings.

The substance is not oil, but scientists at the California Department of Fish and Wildlife still don’t know what it is or where it came from. In the meantime, the International Bird Rescue center in Fairfield, CA. is continuing to nurse the birds back to health. As of yesterday, it had released 81 birds back into the wild and today it will release around 30 more.

A total of 261 birds have died — either brought to the center dead or collected in the field — and the rescue center has 132 still in its care.

The event sheds light on the tricky nature of identifying polluting compounds from an expanding list of such compounds and an alarming increase in the rate of animal die-offs.

“The contaminant is very unusual,” Russ Curtis, online communications manager at International Bird Rescue, told Planet Experts. “In our 44 years of existence, no one can recall responding to an incident like this where we didn’t know what the material was in a couple of days.”

“There are a lot of new chemicals introduced every year, including for pesticides and pharmaceuticals,” said Gail Cho, a staff chemist in quality assurance at the California Department of Fish and Wildlife. “They do end up in the environment.”

Nonetheless, she noted that in her five years at the department, this is the first time that she has seen a contaminant that the agency has been unable to identify after running it through its battery of tests.

Cho and her team have been testing samples to try and figure out what the substance is. She said that the group has analyzed it using both liquid chromatography and gas chromatography — separation techniques that first convert the substance into either a liquid or gas form and then work to separate out the individual components.

They ran the substance on both machines and – despite the 65,000 compounds catalogued in their library – did not find a match. “There are many, many more compounds that exist,” Cho said.

Now the department is working with private laboratories that have different instrumentation to try and figure out what it is.

If the department is able to identify the compound, the next step will be to try and fingerprint it, Cho said. Typically, when something like an oil spill happens, it is possible to trace the oil back to the specific spill site and responsible party, which is then responsible for paying for damages. In this case, Cho said, it is unclear whether they would be able to trace the contaminant back.

The contaminated birds were found in an area that spanned approximately 10 miles near the shore and it is unclear whether the substance was purposefully dumped in one spot or whether it leaked from a moving boat and how far it spread from the original dump site.

“We don’t have any idea who released it or where it came from,” Curtis said.

Living in a Toxic Soup

Jonathan Evans, Environmental Health Legal Director and Senior Counsel at the Center for Biological Diversity, said that it is alarming that the compound remains unknown.

“It’s staggering that the experts have been going through all this testing and haven’t been able to figure it out,” Evans said.

He said the event points to the much larger issue that “we are essentially living in a toxic soup of industrial chemicals and pollutants” that are allowed to be used despite not having a good understanding of potential negative health consequences.

While this specific type of die-off — caused by an unknown substance from an unknown source — may be relatively rare, there is concern that such die-offs may be becoming more common.

A recent study published in the Proceedings of the National Academy of Sciences examined 727 die-offs between 1940 and 2012 and found that such events are increasing in frequency among birds, marine invertebrates and fish. As reported by Planet Experts, the study also found that the major causes of those die-offs were disease, biotoxins, and man-made disturbances like overfishing.

Evans noted that die-offs are also occurring that cannot be pinpointed to a specific cause. For example, he said that over the last several months, between 50,000 and 100,000 Cassin’s auklets, a species of seabird, have washed ashore from Northern California to Washington, having apparently died of starvation. “That is roughly five times larger than any other sea bird die-off since 1980,” he said.

Scientists have not settled on a specific cause for the deaths. Warmer waters, as well as a population boom leading to increased food competition, are both suspected as playing a role.

Warmer waters may also enable diseases to prosper that are unable to survive in colder waters, Evans said.

Bird Baths

The mystery goo that plagued birds in the San Francisco Bay has proven especially difficult to clean off, Curtis said. Typically, when the rescue center receives birds impacted from an oil spill, Dawn dish soap does the trick. “But it was tough to get off.”

Instead, Curtis and others used a combination of baking soda and vinegar followed by a bath of Dawn. Then they rinse the birds in high-pressure showers to blast off any remaining residue.

The goal of the cleansing is to re-waterproof the birds, Curtis said. The substance coats the birds’ feathers and causes them to essentially freeze to death from the cold Bay waters.

Before being released, the birds’ vital signs are checked to make sure they are healthy enough to re-enter the wild. The birds are also tagged so that they can be tracked. “That’s a key part of our response and long term strategy,” Curtis said.

The International Bird Rescue Center is accepting donations to cover the $10,000 per day cost of caring for the birds.