Well if your cats are the type to hunt your ducks then i would be very concerned. My farm cat doesn't, and yes he's been around ducklings, he has no interest.
Calls are highly pred prone, they fly very, very, well, which is basically the only line of defense they have. It's probably the #1 cause of loss with calls, there miniature size and highly pitched tone of the female, only magnifies that.
My calls are penned.