In flight, Common Cranes (Grus grus) scream approximately every ten to fifteen seconds. It is a persistent and loud “krou krou” which can be heard for several miles. The strength of their scream is a result of the bird’s hollow sternum in which the windpipe loops. Courtship displays are performed all year round, even outside the breeding season. Jumps with wings wide open, curtsies, pirouettes, runs, and neck undulations are followed by the usual screams from both partners. The couple forms for life and separates from the group to nest.