Incestuous broods of the Whooper Swan Cygnus cygnus in Poland

We describe a rare case of incestuous broods of Whooper Swan Cygnus cygnus in Świętokrzyskie province, Poland. A sibling pair laid eggs and hatched young at the same site in 2010 and in 2011, nine kilometres from their own hatching place. Both broods were unsuccessful; the young died before autumn. We assume that the key factors explaining the inbreeding were the small local population and that Whooper Swans tend to disperse over short distances.