The world populations of birds, amphibians, mammals, and fish fell overall by 52 percent between 1970 and 2010, far faster than previously believed, the World Wildlife Fund reported.
The group's Living Planet Report, published every two years, said humankind's demands were now 50 percent more than nature can bear.
"This damage is not inevitable but a consequence of the way we choose to live," Ken Norris, Director of Science at the Zoological Society of London, said in a statement, according to Reuters.
There is still hope if politicians and businesses take the right action to protect nature, the report said.
"It is essential that we seize the opportunity - while we still can - to develop sustainably and create a future where people can live and prosper in harmony with nature," said WWF International Director General Marco Lambertini, according to Reuters.
Preserving nature isn't just about protecting wild places, but also about protecting the future of humanity, "indeed, our very survival," Lambertini added.
The biggest declines were in tropical regions, especially Latin America, according to the report. The WWF's "Living Planet Index" is based on trends in 10,380 populations of 3,038 mammal, bird, reptile, amphibian and fish species.
The average decline was much bigger than previously believed, mainly because earlier studies had relied on readily available information from North America and Europe, WWF said.
The same report put the decline at 28 percent between 1970 and 2008 two years ago.
The worst decline was among populations of freshwater species, which dropped by 76 percent over the four decades to 2010. Marine and terrestrial numbers fell by 39 percent, according to Reuters.
The group said the main reasons for declining populations were the loss of natural habitats, exploitation through hunting or fishing, and climate change.
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