WWF’s 2018 Living Planet Report finds that population sizes of thousands of vertebrate species have declined by 60%, on average, between 1970 and 2014, land degradation seriously impacts 75% of terrestrial ecosystems, and current species extinction rates are 100 to 1000 times higher than the background rate. The report attributes these impacts to rising demand for land, water and energy, and explores the impacts of agriculture, fisheries and deforestation.
Note that the average 60% decline in the population sizes of the species considered does not mean that the total number of animals across all of the species considered has decreased by 60%, in contrast to the claims of some media headlines. For further discussion, see this blog post from the Zoological Society of London.
See media coverage here: Widely misinterpreted report still shows catastrophic animal decline (National Geographic), Wait, Have We Really Wiped Out 60 Percent of Animals? (The Atlantic) and Australia's east coast named as 'deforestation front' in WWF Living Planet report (The Guardian).