One in four mammal species could be extinct within 50 years, largely as a result of human actions. One in eight bird species also faces being wiped out along with a third of amphibians, according to the World Conservation Union, which monitors 41,000 species. . . The union says that the rapid extinction rate is between 1,000 and 10,000 times higher than the expected, natural rate. It warns that humans are to blame. Urbanization, agriculture, deforestation and hunting all cause loss of habitat - the biggest danger to plants and animals. Climate change is also thought to be an increasing threat. . In the past 500 years, human activity has forced 820 species to extinction.
