If the police departments are actually fortuitously finding baby ducks, sure...that's smart PR. But if the entire event is staged, that's propaganda instead of PR.
Propaganda and PR are the same thing. The term "public relations" was invented in the wake of public sentiment turning negative regarding "propaganda" in the wake of the second world war. Prior to that PR was just called propaganda, and did not have a generally negative connotation.
It's propaganda either way because it's funded by public money (PR is funded by private money).
If it's staged, then it would border into animal mistreatment since the ducklings would have been removed from their environment to be used as prop.