Why Animals disappearing from the zoo?

In my childhood when i visit Delhi (india) zoo with family, many wild and rare animals were found to be seen. But now there were very few animals to watch. And that too in dull and sick condition. Due to hunting and dwindling forest areas, the government has already banned the circus. Some wild animals have been kept in the category of rare. In the absence of increasing pollution, limited space and proper eating habits, the condition of the birds and animals of the zoo is worrying. The government needs to pay more attention to this.