A new biodiversity survey projects staggering losses of animal life on the planet as a result of human threats such as habitat destruction and poaching, with two-thirds of monitored vertebrate creatures expected to be lost by 2020.

The World Wildlife Fund’s Living Planet Report is based on data from the Zoological society of London and covers more than 14,150 monitored populations of 3,700 vertebrate species. According to the data, species declined by an average of 58 percent between 1970 and 2012, and if current trends continue the number will rise to 67 percent, the researchers said.

Monitored populations of freshwater and terrestrial species fell an average of 81% and 38%, respectively. The most common causes of the declines are loss of living space and illegal killings, followed by pollution, invasive species and disease, and climate change.

African elephants are a startling example of the scale of such losses, the report says, with the population in one area of Tanazania falling from 44,806 individuals in 2009 to 15,217 in 2015, or 66 percent, according to the Tanzania Wildlife Research Institute.

The researchers believe that the establishment of protected areas has slowed the fall of land animal populations overall compared with marine life.

The report warns that a sixth mass extinction event may already be under way, noting that “This is the first time a new geological epoch may be marked by what a single species (Homo sapiens) has consciously done to the planet — as a opposed to what the planet has imposed on resident species.”

Expanding on this grim vision, the study outlines a future in which megalopolises such as New York or Tokyo have been reduced to complex fossils buried in manmade layers of rock. The researchers call for rapid development of sustainable energy, a reduction in the consumption of animal protein, and environmentally friendly agricultural systems.