Which zoo has the most endangered animals

Maybe Bronx Zoo, Chester Zoo or Zoo Antwerpen (this one has many endangered bird species)
 
My guess would be Shedd Aquarium. They have the most animal species, so it would make sense they have the most endangered ones, too.
 
According to ZTL, here is a list of zoos with 3 or more endangered types of mammals:

6: Taipei: Aye-aye, Grey gibbon, Chinese pangolin, Chinese leopard cat, Bengal tiger, Sumatran elephant

5 Al Ain: Arabian leopard, Dama gazelle (nominate subspecies), Nubian red-necked gazelle, Speke’s gazelle, Arabian tahr

Prague: Ganzhorn’s mouse lemur, Malayan slow loris, Mexican spider monkey, Javan leopard, Sri Lankan elephant

4 Berlin TP: Coquerel’s sifaka, Javan leopard, Bawean deer, southern mountain reedbuck

Cologne: Matchie’s tree kangaroo, Greater bamboo lemur, Coquerel’s sifaka, Sri Lankan elephant

Singapore Zoo: Proboscis monkey, red-shanked douc langur, western purple-faced langur, Sri Lankan elephant

3 Chester: Aye-aye, Coquerel’s sifaka, Grandidier’s vontsira

Frankfurt: Eastern quoll, aye-aye, south-central black rhinoceros

Jersey: Comoro flying fox, aye-aye, golden-rumped lion tamarin

Sharjah: Arabian leopard, slender-horned gazelle, Arabian tahr

Singapore Night Safari: Javan slow loris, Malayan slow loris, Dhole (non-specific)
 
According to ZTL, here is a list of zoos with 3 or more endangered types of mammals:

6: Taipei: Aye-aye, Grey gibbon, Chinese pangolin, Chinese leopard cat, Bengal tiger, Sumatran elephant

5 Al Ain: Arabian leopard, Dama gazelle (nominate subspecies), Nubian red-necked gazelle, Speke’s gazelle, Arabian tahr

Prague: Ganzhorn’s mouse lemur, Malayan slow loris, Mexican spider monkey, Javan leopard, Sri Lankan elephant

4 Berlin TP: Coquerel’s sifaka, Javan leopard, Bawean deer, southern mountain reedbuck

Cologne: Matchie’s tree kangaroo, Greater bamboo lemur, Coquerel’s sifaka, Sri Lankan elephant

Singapore Zoo: Proboscis monkey, red-shanked douc langur, western purple-faced langur, Sri Lankan elephant

3 Chester: Aye-aye, Coquerel’s sifaka, Grandidier’s vontsira

Frankfurt: Eastern quoll, aye-aye, south-central black rhinoceros

Jersey: Comoro flying fox, aye-aye, golden-rumped lion tamarin

Sharjah: Arabian leopard, slender-horned gazelle, Arabian tahr

Singapore Night Safari: Javan slow loris, Malayan slow loris, Dhole (non-specific)

This post caught my eye. If true, this list shows how pitifully few endangered species are kept in zoos. Luckily, this is not true.

So I did my own search, limited it to major Dutch zoos, and I only searched for mammals categorized as Critically Endangered or Extinct in the Wild, and using the same source (ZTL). The results of zoos with more than three hits:

Amersfoort has three (Scimitar-horned oryx, golden-bellied capuchin and woylie).
Overloon has three (Lac Alaotra bamboo lemur, golden-bellied capuchin, black-and-white ruffed lemur).
Dierenrijk has three (Visayan warty pig, northern white-cheeked gibbon and red ruffed lemur).
Ouwehands has four (Bornean orangutan, eastern bongo, roloway guenon and western lowland gorilla).
Artis Amsterdam has five (Scimitar-horned oryx, cotton-top tamarin, red-ruffed lemur, celebes crested macaque and western lowland gorilla).
Gaiazoo has five (Europen mink, European hamster, golden-bellied capuchin, eastern bongo and western lowland gorilla).
Beekse Bergen has seven (belted black-and-white ruffed lemur, red-ruffed lemur, black rhinoceros, Kordofan giraffe, addax, western lowland gorilla and Père David's deer).
Rotterdam has nine (Amur leopard, Visayan warty pig, cotton-top tamarin, mhorr gazelle, black rhinoceros, eastern bongo, celebes crested macaque, sumatran tiger, western lowland gorilla).
Apenheul has ten or eleven, depending on if you count subspecies separately (Lac Alaotra bamboo lemur, Bornean orangutan, golden-bellied capuchin, black-and-white ruffed lemur (ssp subcincta and variegata), crowned sifaka, northern white-cheeked gibbon, red ruffed lemur, blue-eyed black lemur, western lowland gorilla and pied tamarin)

So the list by @Dassie rat is very incomplete. I expect that not all these zoos actually have a meaningful impact on all endangered species they hold, but that's not the question of this thread.
 
I started doing a list of all the endangered and critically endangered mammals kept at ZTL zoos and my computer file crashed , so I restricted my list to mammals kept at up to 5 collections. I'm sorry, I should have said that before.

Compiling a list of all ZTL zoos containing endangered is unwieldy, as some animals, such as ring-tailed lemurs, are kept at hundreds of zoos.
 
I am pretty sure that quite a few zoos keep some of their behind-the-scenes animals a secret.

Not exactly relevant to the conversation at hand but most European zoos are quite transparent about their bts species, in stark contrast with the US.
 
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