The World Wildlife Fund released a report Monday saying it has found an "astonishing" 60 percent decline in wildlife populations globally over the last 40 years, mostly due to human activity, including climate change and habitat loss.

"This report sounds a warning shot across our bow. Natural systems essential to our survival – forests, oceans, and rivers – remain in decline. Wildlife around the world continue to dwindle," said Carter Roberts, president and chief executive officer of WWF-US. "It reminds us we need to change course. It's time to balance our consumption with the needs of nature, and to protect the only planet that is our home."

The group's biennial report said it measured trends in 16,704 populations of 4,005 species of birds, mammals, reptiles, amphibians, and fish. The biggest declines were among creatures that live in fresh water, which faced an even bigger 83 percent drop. South and Central America were hit hardest as rain forests shrank, with 20 percent of the Amazon disappearing.

"Humanity and the way we feed, fuel, and finance our societies and economies is pushing nature and the services that power and sustain us to the brink," the report states.

Human activity has had an impact on oceans, forests, coral reefs, wetlands, and mangroves, the report says. The globe has lost about half its shallow-water corals in the last 30 years.

"From rivers and rain forests, to mangroves and mountainsides, across the planet our work shows that wildlife abundance has declined dramatically since 1970," said Ken Norris, director of science at the Zoological Society of London, which provided one of three indexes used to write the report. "The statistics are scary, but all hope is not lost. We have an opportunity to design a new path forward that allows us to coexist sustainably with the wildlife we depend upon. Our report sets out an ambitious agenda for change."

As an example of the trend, Temple University biologist S. Blair Hedges reported Tuesday in the Proceedings of the National Academy of Sciences that he and a team of researchers had found a near-total loss of Haiti's primary forest and a mass extinction of species. Hedges and his colleagues scrutinized aerial photography and Landsat images from 1988 to 2016, finding that forests covered 4.4 percent of Haiti's land in 1988. That plunged to 0.32 percent by 2016.

John Cecil, vice president for stewardship at New Jersey Audubon, said that he had not yet seen the World Wildlife Fund report, but that it was in line with previous research.

"We're finding a broad decline in species across the board," Cecil said, noting exceptions, such as white-tailed deer and Canada geese. "There are a lot of species out there not threatened with immediate extinction, but compared to 50 or 100 years ago, their populations have declined dramatically."

Previously, habitat loss was by far the biggest driver of species loss, he said. Now, he cites climate change and invasive species as among the top reasons. Both alter the habitat, for example, of birds who can no longer find the insects they once fed on or plant life they depended on because "they're all interconnected."

"The birds are failing where the non-native species are taking over," Cecil said. "We're seeing major changes. These global trends are consistent in the United States and East Coast."

More positively, the World Wildlife Fund report said habitat restoration and other actions have worked, citing population increases in giant pandas, mountain gorillas, and endangered dolphins.

It singled out the U.S. Endangered Species Act of 1973 as helping "an estimated 99 percent of listed species avoid extinction."

Among other findings:

  • Habitat suitable for mammals dropped 22 percent from 1970 to 2010, with the greatest declines in the Caribbean, where it exceeded 60 percent.
  • The index measuring extinction risk for birds, mammals, amphibians, corals, and cycads (an ancient group of plants) showed declines for all groups, with species moving more rapidly toward extinction.
  • Humans have already pushed some areas beyond their limits through climate change, loss of biosphere, nitrogen and phosphorous flows, and land-use change.
  • Ninety percent of the world's seabirds are estimated to have plastic fragments in their stomachs.