Photos: The world's critically endangered species Black rhino – Poachers and hunters are responsible for the early decline of black rhino population. The world's animal population has halved in 40 years as humans put unsustainable demands on Earth, according to a 2014 report from the World Wide Fund for Nature Hide Caption 1 of 12

Photos: The world's critically endangered species Hawksbill sea turtle – The existence of Hawksbill sea turtles have been traced back 100 million years. Now they are critically endangered, the WWF says. Hide Caption 2 of 12

Photos: The world's critically endangered species Mountain gorilla – As humans move more into the mountain gorillas' territory, the gorillas have been pushed farther up into the mountains, forcing them to endure dangerous and sometimes deadly conditions, the WWF report on the planet says. Hide Caption 3 of 12

Photos: The world's critically endangered species Amur leopard – Amur Leopard, a rare species of leopard living on the borders of Russia and China, was the winner of the 2013 WWF award dedicated to the positive evolution of an endangered species, but remains critically endangered. Hide Caption 4 of 12

Photos: The world's critically endangered species Sumatran orangutan – Sumatran orangutans are losing their natural habitats to mining, palm oil and paper plantations. Hide Caption 5 of 12

Photos: The world's critically endangered species South China tiger – The South China tiger is considered "functionally extinct," as it has not been sighted in the wild for more than 25 years. Hide Caption 6 of 12

Photos: The world's critically endangered species Sumatran elephant – Sumatran elephants come into conflict with humans due to the rapid expansion of palm oil plantations which destroy their habitat. Hide Caption 7 of 12

Photos: The world's critically endangered species Sumatran tiger – Sumatran tigers are the smallest surviving tiger species and are protected by law in Indonesia. But despite increased efforts in tiger conservation, they remain critically endangered. Hide Caption 8 of 12

Photos: The world's critically endangered species Leatherback turtle – Leatherback turtles are the largest sea turtle species and also one of the most migratory, crossing both the Atlantic and Pacific Oceans. According to WWF, their numbers have seriously declined during the last century as a result of intense egg collection and fishing. Hide Caption 9 of 12

Photos: The world's critically endangered species Western lowland gorilla – Western lowland gorillas are critically endangered species. Because of poaching and disease, their numbers have declined by more than 60% over the last 20 to 25 years, according to the WWF's report. Hide Caption 10 of 12

Photos: The world's critically endangered species Yangtze finless porpoise – The population of Yangtze finless porpoises is declining rapidly. The freshwater dolphins are suffering due to pollution and hunting. Hide Caption 11 of 12