Since Writhedhornbill declared "less then 3 holders" to be rare, here's my list, anyone for some more ideas?
- Saiga Antilope (only held at Cologne Zoo 2.0)
- Douc Langur (only held at Cologne Zoo 1.3.1.1)
- Orinoco River Dolphin (only held at Duisburg 1.0)
- Pangolin (only held at Paris ... think Jardin des Plantes with 1.0)
- Black Saki (only held at Mullhouse Zoo 0.1)
- Panay Cloudrunner (afaik only held at ZSL)
- Kaka (only held at Stuttgart Zoo, think 1.3.0.0)
- Baird's Tapir (only held at Wuppertal Zoo, think 2.3.0.2)
- Birds of Paradise (a few species held at Cologne, Bird-park Walsrode and chester)
- Kiwi (think 2, Frankfurt & Berlin Zoo)
- Four-horned Antilope (Berlin Zoo & Paris Jardin)
- Little Fairy Pinguin (afaik Cologne, is there still a colony in England?)
- Steller sea-lion (afaik 2, Harderwijk & Moscow)
- Walrus (afaik, Harderwijk & Moscow)
- Yellow-backed Duiker (Wuppertal & Nurnberg)
- Tayra (afaik 2, Berlin & Praha)
- Cape hartebeest (Hannover & Arnhem)
- Mountain Paca (afaik Antwerp & Zoo Dvur Kralove)
- Giant Panda (Berlin Zoo & Vienna)
- Gharial (afaik only 1 in Denmark, maybe one or two more in france?)
- Beluga Whale (Valencia & Moscow)
- Killer Whale (Tenerife & Marineland Antibes)
- Chinstrap Pinguin (Madrid.. & Tenerife?)
- Japanese giant salamander (Antwerp)
- Mountain Anoa (Wuppertal & Decin)
- Weddel's Tamarin (Epe)
- Agile Mangabey (Epe)
- Blue-faced mangabey (Gelsenkirchen)
- Bighorn Sheep (Arnhem)
- Black-faced Impala (Barcelona & Lisbon)
- Crab-eating Raccoon (Usti)
- Tuatara (Chester & Berlin Zoo)
Birdpark Walsrode, the biggest birdpark has such an incredible collection with so so many rarities that i would estimate that park to have at least 20 birdspecies that are only held at that park, same with Loro Parc Tenerife (MANY rare parrots in their breeding facility, like the Spix' Macaw)...
Also many subspecies are kept at only one or two institutions for example golden takins, south-east asian leopard, Javan Leopard, Nubian giraffes, northern tamandua, Northern White Rhino, Eastern Lowland gorilla, Red howler monkeys, and some species of spider monkey...
The list could probably be a lot bigger with reptile and amphibian species...