I think it'd be a wise idea to consider the number of predators you have, whether your pens are secure, and whether you're willing to accept some loss if the predator population is high or your fencing inadequate to prevent predators from gaining access before you decide to intervene or not. Things to think of are crows, owls, eagles, hawks, dogs, feral cats, raccoon, fox, mink, etc. You might not know you have a problem until it's too late. Are neighbor's dogs a concern? Are their kids? Unfortunately as distasteful as it is at times you can have 15 ducklings one day and 0 the next and it's not until it's too late that you realize that you have potential problems.
HTH