There are many species of ducks in Japan, but I believe these are Kamo, the common mallard.
They were and are eaten, and their arrival in the Autumn was used as a seasonal marker in poetry.
There has recently been a renewed interest in the use of domesticated ducks in rice agriculture. Traditionally they were used to control weeds and insects in the paddies as well as adding fertilizer.
All these were photographed in Chofu, Yamaguchi.