I watched this film when I was younger. It was about a family of bunnies who lives on a boat
The mother bunny got taken by a large bird- the
Young bunny goes if a adventure to find his mother. He goes to this large distopian city. And finds bird king and later his mother in a small house . She was surrounded by glass bottles from the young bunny, who had sent him letters in bottles
THATS ALL I REMEMBER. I HAVE SPENT HOURS LOOKING FOR IT 
PLEASE HELP ME