Washington Post: Planet Earth lost a tenth of all wilderness in past two decades
Tim Boucher
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Ecowatch: Half the World’s Animal Population Vanished Since 1970

From 2014, but seems to dovetail a little too perfectly with the linked article above about having lost 1/10th of wilderness in past two decades:

The just-released tenth biennial edition of the World Wildlife Fund (WWF) Living Planet report found that between hunting, habitat destruction, environmental degradation and the effects of climate change, the world’s animal populations of mammals, birds, reptiles, amphibians and fish has dropped 52 percent since 1970. The study, produced in partnership with the Zoological Society of London, Global Footprint Network and Water Footprint Network, measured 10,000 species.