A personal experience about this topic is when I went the zoo a while ago i noticed that a lion wasn't really belonging in his exhibit because it was too small for him to live in. It wasn't big enough and it didn't seem like his true habitat. Animal cruelty inside the zoo and there living ways inside the zoo. They shouldn't be in a cage surrounded by people and looked out 24/7. The zoo keepers shouldn't be scared of the animals because it's more scared of him.
The major problem with zoos is that the animals who live there are kept in enclosures that don't allow them to live their life like they normally should. Zoo animals have to spend repeated days and years in the exact same enclosure. For example the San Diego zoo has a polar bear and he doesn't live in the habitat that he should be instead he is living on hard rock floor. He isn't getting the coldness that he usually should get in Alaska or Greenland.
The issue with this cause is that the animals need to live out their lives in their real habitats not a enclosure. And it also makes them not able to live back in the wild if released. They wouldn't be able to survive and adapt to their old ways, because they wouldn't know how to hunt anymore after just being given food.
Some of the many causes of animal cruelty in zoos are that the zookeepers are scared of the animals so they use force. The animals are also scared to begin with so they fight back when force is being used so it makes it worse. Another cause of this is that the animals just feel cornered in those kind of situation and have to fight their ground. Also there breeding programs stress the animals to their limits and they feel like they're in danger so they attack.
I would say that a call to action would have to that we have to get more qualified zoo keepers and make sure that those who fund or the people or perform check ups on the zoo's perform better and actually check the little things that could become a problem. We would have to start of shelters for those animals and help them get back into the wild where they belong and show them how to hunt in the wild.