SAN DIEGO -- A cockfighting raid over the weekend in San Diego is being described as the biggest in U.S. history.

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Agents found 4,400 birds Saturday at a 7-acre compound in Nestor, near the Otay Mesa industrial area of San Diego. More than 2,500 birds were seized at the same place six years ago in what was then the largest bust in history. Hundreds more birds were found at a second training ground nearby, officials said.

Fifty people were issued misdemeanor citations, punishable by up to one year in jail and a $5,000 fine, and ordered to answer to cockfighting charges in early December, said Paul Levikow, a spokesman for the San Diego County District Attorney's office. Another 50 people are still being sought, authorities said.

The cockfighting operation was managed and patronized largely by Filipinos, and fights were staged in the San Diego area, an official said. Many birds were sent to the Philippines or Hawaii.

A first offense for cockfighting is a misdemeanor in California. A second offense ratchets it up to a felony.

"This is what we call a life-to-death operation for these birds," said Lt. Dan DeSousa of the San Diego County of Animal Services. "They were raised on site. They would sell the eggs to people that wanted a championship bloodline for these birds."

At a news conference held Monday at the county district attorney's office, officials displayed paraphernalia typically used in cockfighting. The state director of the Humane Society gave a grisly description of what happens at a cockfighting event.

"Both birds will typically attack each other, collide somewhere in the pit, and it will be just a bloody blur of feathers," said Eric Sakach. "Birds are literally being mutilated, sliced right there. Whole appendages can fall off."

More arrests are expected, officials said on Monday.

About 80 percent of the birds seized have been euthanized, Levikow said.