To have an idea you can look at this https://zoo.sandiegozoo.org/content/animals-plants
Dozens...possibly 100's if you count all the birds, snakes and reptiles. They have many animals I hadn't had the chance to see anywhere else: pandas, red pandas, snow leopards, black panthers, savannah cats, grizzly bears, koalas, polar bears, king cobras and cheetahs. And of course the flamingos, crocodiles, tigers, giant tortoises, elephants and giraffes that most zoos have as well.
That's a hard question to answer. I can say that the zoo requires at least 5 to be visited fully, not including time to rest and eat.
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