Birds are considered to be a good indicator of the condition of the natural environment.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/15-indian-birds-among-100-globally-endangered-species
[2] http://admin.indiaenvironmentportal.org.in/category/author/vijay-pinjarkar
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/times-india-new-delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/india
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/birds
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/endangered-species
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/grasslands
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/bombay-natural-history-society-bnhs
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/wildlife