It was often said in Berkshire: "When the big magpie and the very small magpie fly over the bridge there shall be good fortune for someone." The saying persisted for centuries, largely because it was impossible to disprove, but also because the type of people who said it would make sure they said it a lot, even when its application was tenuous at best to the preceding dialogue.
A local saying that has not lasted so well is: "When the bat flies out the dell, electricity and water will mix well." People finally stopped saying this in the region after several electrocution fatalities at or around dusk.
Maidenhead United still use the magpie aphorism because visitors to the area like it when crusty old townspeople say it to them because of course this is what living in a country town is all about. That and very poor theatre. Cameron Carter