On the few occasions I let a muscovy hen do as she wishes with her ducklings all died. I don't believe they bring them back to the food enough, I recommend keeping them locked up for a week or two. I have rounded mine up, I take a 5 gallon pail to put ducklings in and a fishing net or a walking stick to block the mom, she should follow the ducklings after you have them, but watch yourself as the mom can be vicious.