Why even think of keeping animals in captivity in the first place?
Birds cage, large or small aquariums for fish or turtles, a zoo, non elevated railway tracks passing through forest, or a jungle, as they also contribute to killing of animals, or injuring them seriously.
These are all man made disasters for the animal kingdom.
Its an irony to think that man has been made the most intelligent of all creatures.
If left to man completely by god or nature, the whole of earth may be a desert very soon.
Do we only know how to construct, destroy, renovate, when hardly any of us know how to even plant trees, or protect them.