Worldwide populations of mammals, birds and other vertebrates have fallen by an average of 52 percent in the past 40 years, according to the Living Planet Index report recently released by the World Wildlife Fund.
Many forms of human activity are responsible for the alarming rate of animal decline. Habitat depletion, overexploitation, pollution, invasive species and other problems all contribute to the loss. Climate change is both a cause and a result of species and habitat loss.