Sad to see this happening even in Bharatpur.
On my recent visit to Karnala Bird Sanctuary (near Mumbai) I found that an NGO from a neighbouring village has joined hands with the FD to start keeping a check on plastics taken inside the sanctuary. They thoroughly check each bag carried by visitors for any plastics. If they find any plastics they keep them along with a Rs.200 deposit, and return them when the visitors leave. In addition, regardless of keeping plastics, they collect Rs.10 from each group of visitors as a fee to keep the place tidy.
The littering in the sanctuary has subsequently been reduced a great deal, especially considering it is a popular weekend getaway for a large number of people from Mumbai.