I would also mention the red-billed oxpeckers. And maybe the chestnut-backed sparrow larks (they have the only ones in Europe according to Zootierliste, but I don't know if they are interesting to anyone but bird enthusiasts, while oxpeckers at least are quite iconic due to nature documentaries).
There are also some rare bird species flee-flying in the Tropenaquarium. Unfortunately, I only managed to see the two species of bee-eaters, bearded barbets, Livingstone's turacos and golden-breasted starlings when I visited, so the others may not be easy to spot.