According to the folk calendar - Kupriyanov Day, Crane Assembly

Christians on this day remember the life and deeds of Bishop Cyprian of Carthage. People believed that on September 13, cranes were preparing to fly to warm countries. Before a long journey, the birds gather in the swamps and agree on how to fly and who to choose as leader. Therefore, sometimes Kupriyanov’s day was called the Crane Assembly or Crane Assembly.