two times now, two seperate Gosslings somehow ended up on their backs, and couldn't get back up. they are larger gosslings (as big as my fully grown ducks) but still have down, but only little sprouts of feathers. they lay their and try to use their stubby wings and head to try to right themselvs until the down is rubbed off and the wings and neck are rubbed raw. it happened once in a cast iron tub with gratting and wood chips on the bottom, and the second time was in the duck pen in the mud right after a rain. They both survived, but they didn't look good when I got to them. why is this happening ????????????