Hippos (not the Pygmy Hippo) require too much space. I downloaded a habitat from the Steam workshop that was made for elephants. It wasn't a massive habitat, but it's big enough to comfortably house four full-grown elephants (of either species). I put three adult hippos in, however, and it barely meets their space requirements, even with modifications to the habitat. This has been an issue ever since the game was released, and I'm far from the first person to bring this up. The habitat I used is comparable in size to, if not a bit bigger than, some real-life hippo habitats at different zoological facilities like the San Diego Zoo and Disney's Animal Kingdom, and those places had good-sized habitats for multiple hippos, adults and/or calves. So, why do hippos require more space than elephants?
Another thing is that the minimum social requirement should be changed from three to one. I've been to zoological facilities with hippos, and they either have them living in groups or solitarily. This should be reflected in the game.
Another thing is that the minimum social requirement should be changed from three to one. I've been to zoological facilities with hippos, and they either have them living in groups or solitarily. This should be reflected in the game.