It's actually 30, not 20 and not a big deal to get. Just one habitat with only like half of the African Savannah grazers will hit it pretty quickly as babies are born. Only takes one keeper to keep them all fed, if you keep all the feeders near the keeper gate they don't even fall behind. And, of course, another one assigned to keep it clean.
This is the kind of habitat where I'm sure I've seen two keepers filling feeders at one time in some of my zoos though (I often have more keepers, and more habitats, in the same work zone), which is why I question the statement people make that only one can be in the habitat on a specific task at a time.
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so thx. 
