We have a Black East Indies duckling here that is about a week old. He's with three other ducklings and a few chicks - all are doing fine other than him. A few minutes ago we went to the cage and saw him standing there. He dropped, convulsed, stopped and came out of it a few seconds later. He's now resting normally, albeit extremely quiet. Does anyone know what this could be or what can be done to keep it from happening again? Thanks.