It has been observed that the number of mammals, birds, reptiles, amphibians and fish across the globe are declining in numbers day by day due to various reasons.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/national-wildlife-week-5-species-will-be-extinct-soon
[2] http://admin.indiaenvironmentportal.org.in/category/author/shruti-saxena
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/zee-news
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/india
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/wwf
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/tiger
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/deforestation
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/poaching
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/environmentalists
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indonesia
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/endangered-species
[12] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rhinoceros
[13] http://admin.indiaenvironmentportal.org.in/category/thesaurus/wildlife