I've got a little group of Elizabeth ducks I raise, all of them get along well but lately one female has been quite strange. She keeps making an unusual 'gurk! gurk!' sound instead of the usual 'quack!' She also used to be lovers with one of the males but everytime he gets out his member for fertilisation she goes 'gurk! gurk! gurk! again and snaps at the member. She won't eat properly even when I cook her something tasty like beef casserole and I'm getting worried, she snaps at me when I try to give her the gravy which she used to love. What could be wrong, why is she so sad and angry?