is this actually an aviary? It appears to just have a fence around it, and it is filled with mallards.
From memory, though I haven't been here about fifteen years, its the open/fenced enclosure you see from the carparking area. I doubt its changed at all since then.
I think it is more of a walk through enclosure than an aviary. I went in 2013 and all I can remember was a lot of ducks.