This day is a United Nations international day to celebrate all the world’s wild animals and plants and the contribution that they make to our lives and the health of the planet. This date was chosen as it is the birthday of CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora, signed in 1973. The United Nations General Assembly proclaimed the 3rd March as UN World Wildlife Day on 20th December 2013.
The website is here.