New Duck

[fowl farm]

Would it be a bad idea to bring another duck into the flock? Would that be taking chances with disease? I mean a bigger duck ( not a cute duckling) Would it cause issues with chickens or guineas? ( I know chickens can carry diseases that don't hurt them but kill peacocks or something) Or would getting new chickens cause issues with my ducks? I pretty much want to know the dangers of bringing new birds to my flock. Whether a full grown is more likely to carry disease than a baby or what and so on and so forth.
I know that's a big question, but I would REALLY like info. As you might have guessed, I'm thinking about getting a new duck ( or possibly new chicken)

 

[FireTigeris]

Any time you are about to add an animal to existing animals there is a chance of diseases passing one way or another, no matter the ages of the animals that will be mixed.

Feed store day-olds are usually inoculated against some common diseases that would cause the destruction of the flock...

no guarantee for older animals.

 

[Amiga]

When a duck and goose rescue organization I know of brings in new animals, they go into a special pen, and get tested for diseases - and treated if necessary - before joining the rest of the flock.

Also, introductions need to be gradual. When I brought Romy and Michele in, they stayed next to the runners the first several nights, to avoid additional anxiety.