The cranes are wise, they can choose, they know, or perhaps better expressed they have the instinct that the wrong time to return means death. It is interesting to look at the statistics from previous years. Through this statistics we can see when we had early springs. 2006 the mass arrivel were at the end of March april but before there had been some vanguard, the first vanguard arrived March 22. The earliest was the year 2007 when the first vanguard came March 5.