And in saying all that, I forgot to mention what I actually entered this thread for: not exactly a zoo, but Swan Lake Iris Gardens is a public park in Sumter, South Carolina that keeps every species of swan, including the not-a-swan coscoroba swan, as well as both sides of a potentially split tundra swan. Supposedly it's the only park, and indeed perhaps only place in the world that keeps every swan species.
It's questionable if they do or not, as some of the photos on their website are incorrectly labeled.