"Forgot to mention...they have my full name, address and phone number...they require it be filled out on a sign in sheet when you being any animals there"
This is what led me to believe something had been 'signed in' would like to see a copy, bet it was a release. If these people haven't been...
OK, since they weren't wild animals but your pets, are you sure the 'sign in sheet' wasn't a release of some type? I would go back and ask for a copy of what you signed, read the small print and if it was not a release (giving them the animal) take it to the police, they are then stolen property...
Were these wild ducks or domestic ducks? I am assuming they were wild since the place was refered to as a wildlife rehab? If they were wild, they weren't yours to get back?