The world was very different in 1970. Internet cat videos weren’t around to distract us. Millennials hadn’t yet graced the planet. Simon & Garfunkel had the biggest hit song of the year.

Another difference?

There were many, many more wild animals living on Earth–about double the number alive today, according to a comprehensive new survey from the environmental conservation group, WWF, and the Zoological Society of London.

Dolphins. Hawks. Iguanas. Pythons. It’s essentially a census.

We often hear about the plight of various endangered species, and the fact of the matter is that experts are starting to think we’re on the verge of a sixth mass extinction in the entire 3.8 billion year history of life on this planet. However, to most people, species are kind of an abstract concept; so is the academic term “biodiversity,” which is so frequently used.

The Living Planet report makes the wildlife crisis hit home in a more shocking, visceral way. It’s counting not species, but numbers of individuals. Dolphins. Hawks. Iguanas. Pythons. It’s essentially a census. And the results are stark: In less than two generations of humans, the populations of vertebrate animals have dropped by 52% between 1970 and 2010.

The survey, conducted biennially, looked at more than 10,000 representative populations of more than 3,000 species of mammals, birds, reptiles, amphibians, and fish. For the first time this year, the researchers then extrapolated this work to create an index that gauges the health of all 45,000 species of vertebrates.

The causes of the die-off have been many, ranging from habitat loss, hunting, and poaching to climate change and water pollution. The biggest declines were seen in the tropics (a 56% reduction) and in freshwater ecosystems, such as rivers and lakes (an average 76% decline). Latin America saw the biggest drops among world regions.