The net cast for illegal immigrants in Sonoma County shrank dramatically in the past year — with far fewer people turned over to the federal government for being in the country without permission. The reasons for that change are hard to pinpoint. But it corresponds chronologically to a decision that local law enforcement agencies — urged on by advocates for illegal immigrants’ rights — made last year to accept Mexican consular cards as valid identification. That meant officers in the field who were confident of the identity of a person they contacted could check them against records, and did not always have to take that person to jail to find out if they were wanted or otherwise posed a threat. Since the new policy took effect, local authorities have turned over just under half as many people as they previously did to Immigration and Customs Enforcement under the federal agency’s Se Communities program, according to data the agency provided.