Here are my ideas for mixed species exhibits:
1: Hippopotamus, Marabou Stork, Great White Pelican, Yellow-Billed Stork
2. Blue Gnu, Sable Antelope, Impala, Cattle Egret, Red-Billed Oxpecker
3. Giant Anteater, Greater Rhea, Cocoi Heron
4. Rock Hyrax, Peach-Faced Lovebird, Speckled Mousebird, Long-Tailed Paradise Whydah, Northern Red Bishop, Common Waxbill, Pancake Tortoise, Common Agama
5. Platypus, New Guinea Snake-Necked Turtle, Australian Rainbowfish
6. Koala, Short-Nosed Echidna, Galah, Blue-Winged Kookaburra, Crested Pigeon,
7. African Crested Porcupine, African Spurred Tortoise
8. Brush-Tailed Rock Wallaby, Superb Lyrebird, Blue-Winged Kookaburra
9. Great Blue Heron, Trumpeter Swan, American Kestrel, River Cooter
10. Coyote, American Badger
11. King Vulture, Crested Oropendola, Scarlet Ibis
12. Belted Kingfisher, Red-Eared Slider,
13. South Polar Skua, Ivory Gull
14. Atlantic Puffin, Pigeon Guillemot, Surf Scoter, Leopard Shark, California Sheepshead, Garibaldi
15. Galapagos Dove, Marine Iguana, Sally Lightfoot Crab
16. Helmeted Vanga, Madagascan Hoope, Radiated Tortoise,
17. Panamanian Golden Frog, Green Vine Snake
18. Green Anaconda, Rainbow Whiptail
19. Bongo, Yellow-Backed Duiker, Black-And-White Colobous, Congo Peafowl, African Gray Parrot, Great Blue Turaco, White-Necked Rockfowl
20. Common Ostrich, Gemsbok, Serval
21. Common Warthog, Honey Badger
22. Aardwolf, Aardvark, Yellow Mongoose, Gray Crowed Crane
23. Reticulated Giraffe, Black-Backed Jackal
1 and 3: depends a lot on wether the birds are pinioned or not. In aviaries this might work very well but in open exhibits the pinioned birds will probably not breed and might even be killed by the hippo in the first one. Marabou might also be troublesome, but this is no guarantee for failure.
2: Oxpeckers can keep wounds open with their pecking, so this is something to watch out for.
4: Don't know how the hyraxes react to these reptiles, but besides that I think similar things have been done already
5: I would think platypus are already hard enough to keep and breed on their own, let alone in the presence of hyperactive turtles (in my memory at least).
6: I would be worried about diseases carried over from the other species to the koala and the kookaburras eating chicks.
7: Has been done numerous times
8: Personally no idea about how lyrebirds do in captivity, let alone in mixed exhibits.
9: kestrels have been mixed with other species before and so have herons and swans. Kestrels with swans would probably be fine and herons with swans might be (chicks could be preyed on). The turtles probably wouldn't kill anything or be killed but aggression and harassing (both ways) is not unlikely.
10: Don't know, wouldn't take the risk myself
11: This would probably work, king vultures have been mixed with other species (including ibises, ducks, flamingoes, penguins, parrots and other vultures) before and this seems to go well.
12: I guess this would work
13: Seems risky, and at least the skua's are not really animals I would recommend in captivity
14: It might work and it might not. The fish might become stressed by swimming/diving birds.
15: No idea
16: I guess it might work if the vanga are capable of handling captivity and are not stressed out by the hoopoe's.
17: Seems like snack time for the snakes, and don't forget things like disease transfer and possible slightly different environmental requirements. If the snakes don't live in cloud forests like the frogs, chances are any attempt at combining them might result in an intermediate environment where neither species is fully satisfied.
18: Seems like a bad idea. I also couldn't find directly wether the whiptails are only found west of the Andes, because this would mean that the two species might never meet in the wild and actually live in slightly different environments. When it comes to reptiles, small differences can be of huge importance for certain species (especially when it comes to breeding).
19: The parrots would almost certainly harass or at least stress out the other birds. The colobus might be a threat to all birds and might cause trouble with male bongo.
20: Seems like a recipe for stress and aggression.
21: Again loads of stress and aggression probably, possibly even deads
22: Cranes and mongoose seems a bad idea, the rest depends a bit though mongoose can be a pain in the ass in mixed exhibits. Without them this would probably work (preferably in an aviary for the welfare of the cranes) if you include spaces that only the cranes can acces.
23: I'm quite curious about this one actually, and not 100% sure that the giraffes would see the small jackals as a treat as long as they keep their distance from the young giraffes.