Volunteers from the Wildlife Emergency Service are putting the ailing birds in boxes and taking them to the International Bird Rescue Center in Fairfield where they will be cleaned up.
So far, volunteers have found more than 200 birds.
Even though the substance is not toxic, rescuers searching Monday afternoon are finding many dead birds. "What's killing them is that they've got this stuff on them that makes them cold. It separates their feathers and lets all the cold air and water in," Wildlife Emergency Service spokesperson Rebecca Dmytryk said.
Rescuers made up a wash that includes soap, vinegar and baking soda to clean the gunk off the birds.
Since it is not clear where the substance is coming from, the rescue groups are paying for the cost of cleaning the animals.
If you'd like to make a donation to help pay for the rescue effort, click here.