At least five birds have been spotted with the collars near Lake Merced, and rescuers are trying to get to them as quickly as they can.
Rescuers said the birds are difficult to capture, though, because of the traumatic abuse they have already suffered. They generally flee when humans approach.
The collars are damaging to the birds' feathers. Rescuers said if they can't catch them and remove the collars quickly, the birds won't be able to make it through the winter.