What is the importance of the zoo in the novel, Ducks, Newburyport?

The zoo is a setting that represents human oppression in Ducks, Newburyport. After spending most of the novel trying to retrieve her cubs from humans, the mountain lioness lands in a cage next to them at the zoo. Her perspective conveys how grossly humans misinterpret her needs and suggests that zoos can never provide adequate homes for wild animals.