Reputable birders in the area reported seeing two to three gulls with cut beer cans on their necks, said Rebecca Dmytryk, spokeswoman for WildRescue in Monterey.
A Budweiser beer can is clearly visible in one photo, and appears to be the brand in another, she said.
Sightings of the birds occurred at Fisherman's Wharf and Alcatraz in San Francisco, and in an undisclosed location in Half Moon Bay.
The first report was in September, but it wasn't made public because they hoped that it was an isolated incident, Dmytryk said. Now that more reports have come in, WildRescue and International Bird Rescue of Fairfield are asking the public for help in finding the birds.
"Please don't try to catch the birds. If you miss, and you probably will, you'll frighten them more. They're already frightened because they've been tortured," Dmytryk said.
It will be nearly impossible to approach the birds if people keep trying to catch them.
"That's what got them into trouble in the first place," she said. What the organizations want is information, and as much of it as they can get. The more information they get, the better they'll understand the birds' patterns, which will increase the chance of rescuing the birds.
"They're going to hang out, usually at a pier or a marina where they can get food easily," Dmytryk said.
Sightings should be reported to a dedicated paging service, (831) 429-2323, or emailed to email@example.com.
Two separate anonymous donors are offering $1,000 each, for a total of $2,000, for the arrest and prosecution of the person, or persons, committing these crimes.
"This is a federal crime punishable by severe fines, imprisonment, or both," Dmytryk said.
The cans pose multiple risks to the birds. They won't be able to preen to keep clean, the cans could get caught on something, and they may not be able to eat.
Both organizations are also looking for volunteers to help with this effort, and any other activities as a volunteer rescuer. Anyone interested will receive training and will be placed on an on-call list. There is a training scheduled for January. More information about the organizations can be found on their websites at www.wildrescue.org, and www.ibrrc.org.