This "Living Planet Index" declined by 52 percent between 1970 and 2010, "a much bigger decrease than has been reported previously," according to the report. The 52 percent figure refers to a general trend of vertebrate species populations shrinking, on average, to about half the size that they were 40 years ago, according to WWF spokesperson Molly Edmonds. The report attributes the declines primarily to habitat loss and degradation, hunting and fishing, and climate change.

The previous WWF report analyzing animal populations, published in 2012, suggested a decline of 28% over a similar period. The latest report uses 15% more data than the previous one, is more representative of tropical species and applies an improved methodology.

"We were surprised by the extent of the decline. It means we are not effectively reducing biodiversity loss," said Robin Freeman, a researcher at the Zoological Society of London, which compiled the population database on which the study was based.

View October 1, 2014 RT article
View September 30, 2014 World Wildlife Fund article
View September 30, 2014 The Wall Street Journal article
View September 30, 2014 National Geographic article
View September 29, 2014 The Guardian article