Scientists are stepping up efforts to identify a mysterious gooey substance polluting waters along the eastern edge of San Francisco Bay, coating hundreds of sea birds and killing scores of them, a state wildlife official said Tuesday.

 

Initial field testing of the slime, first reported on Friday, came back negative for petroleum but authorities hope a more comprehensive laboratory analysis will provide some conclusive results, said Andrew Hughan, spokesman for the California Department of Fish & Wildlife.

 

More than 100 birds, mostly ocean-going water fowl, have died after their feathers became soaked in the colorless, odorless goop, impairing their ability to insulate themselves from cold and leading to hypothermia, Hughan said.

 

Rescue teams from two private volunteer groups have captured and cleaned some 300 or more contaminated birds that they hope to return to the wild, he said.

 

On Tuesday, sandpipers and other species of shore birds were being found tainted by the substance, according to Rebecca Dmytryk of Wildlife Emergency Services, one of the two rescue groups.

 

"This has been incredibly difficult and taken a lot of time per bird," she said.

 

The viscous substance was more obvious when it first appeared in the bay late last week but the contamination of shore birds suggests that the material has been slow to dissipate in the environment, Hughan said.

 

“It was thick enough to see in the water for a few days and now you can’t really see it unless you know where to look,” he said. “It’s a real mystery. We’ve never seen anything like it and neither have the bird rescuers.”

 

In some cases birds that appear to be in distress fly off before they can be caught, leaving rescue teams unable to capture a bird "unless it is really fouled," he said.

 

“We don’t expect more mortality from the rescued birds but many more birds are out there that will die of exposure," he said. "This issue has tremendous priority within the department.”

 

 

PHOTO: A bird is cleaned at the International Bird Rescue in Fairfield, California January 20, 2015.

CREDIT: REUTERS/ROBERT GALBRAITH.