It's not just people who have left the farm in droves and moved to the city. At times, it seems as if the entire California population of crows has migrated into urban areas, raising concerns over fouled yards, walkways, buildings and vehicles beneath and near roosts. In Northern California's Yuba City the crow population recently grew to an astonishing 1 million birds. Since traditional methods of dispersing crows -- trapping, poisoning or frightening with noise-making devices -- are inappropriate for city use, local officials began investigating alternative methods. Paul Gorenzel, a researcher with the UC Davis wildlife, fish and conservation biology department, has been monitoring some of these non-lethal techniques. They make use of mylar tape, strobe lights, netting, pyrotechnic devices, water-misters and even the pre-recorded threat of predatory owls. Gorenzel's own research has focused on pre-recorded crow distress calls, now being used in Sutter County. He is reporting his findings in a number of scholarly journals.