This is the big cage in the center right? They where in there alright, certainly when I did an intership on this section. Although there where never visible, one of the keepers showed them to me. They know live in Duisburg I think. So much has changed over time, I actually helped building there current free-flight sections!
OK didn't know that, I only remember them being in the smaller cages oposit of the Hyasinth macaw-aviary. I can remember this cage was also used as kind of Australian aviary with Palm cockatoos and Thickknees. @Rupicola: job well done, I like these free-flight sections very much !