May 04, 2015 09:50 AM EDT By Russell Westerholm, UniversityHerald Reporter

The mass decline of the Earth's biggest plant-eaters is concerning scientists, as they are noticing less and less rhinos, elephants, gorillas and more.

According to BBC News, authors of a study published in the journal Science Advances found 60 percent of large herbivores are possibly facing extinction. For their study, the researchers at Oregon State University (OSU) analyzed 74 such species that weighed in at 100kg at the least.

"I expected that habitat change would be the main factor causing the endangerment of large herbivores," study lead author William Ripple, a wildlife ecologist at OSU, said in a press release. "But surprisingly, the results show that the two main factors in herbivore declines are hunting by humans and habitat change. They are twin threats.

"Our analysis shows that it goes well beyond forest landscapes, to savannahs and grasslands and deserts. So we coin a new term, the empty landscape."

Joined by an international team of scientists, Ripple determined the root causes for this mass population decline are poaching and loss of habitat. Herbivores are not alone either, as carnivores are going through a similar problem.

"The big carnivores, like the charismatic big cats or wolves, face horrendous problems from direct persecution, over-hunting and habitat loss, but our new study adds another nail to their coffin - the empty larder," David Macdonald, of Oxford University's Wildlife Conservation Research Unit, told BBC News. "It's no use having habitat if there's nothing left to eat in it."

The new study adds to a growing discussion about the harmful effects poaching has on the environment and how government leaders can effect change through policymaking.

"We hope this report increases appreciation for the importance of large herbivores in these ecosystems," Ripple said. "And we hope that policymakers take action to conserve these species."

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