DURATION: 1:05-----------------------------------------SHOTLIST:AP TELEVISION - AP CLIENTS ONLYSt. Paul, Minnesota - March 13, 2013STORYLINE: It's been a tough winter for owls in parts of North America, and the evidence is turning up on roadsides, at bird feeders and at a wildlife rehab center in Minnesota. The dead, injured and sick owls are symptoms of what ornithologists call an "irruption." It's a natural, cyclical phenomenon that happens when hungry owls that normally winter in northern latitudes in Canada head south to seek food _ either because their normal food of mice, voles and lemmings are in short supply or heavy snow cover makes small rodents difficult to find. Other irruptions have been reported recently in New England, as well as southern Ontario and Quebec, and parts of British Columbia. Experts stress that what's happening now happens regularly and to a varying mix of owl species.