Africa's savanna elephant population plummeted by about 30 per cent from 2007 to 2014 and is declining at about 8 per cent a year, said a survey funded by Microsoft co-founder and philanthropist Paul Allen.
"If we can't save the African elephant, what is the hope of conserving the rest of Africa's wildlife?" elephant ecologist Mike Chase, the lead researcher, said in a statement. "I am hopeful that, with the right tools, research, conservation efforts and political will, we can help conserve elephants for decades to come."
The study, known as the Great Elephant Census and involving 90 scientists, estimated a population of 352,271 savanna elephants.
Overall, researchers spotted about 12 carcasses for every 100 live elephants, indicating poaching at a high enough level to cause population decline. But the rates were much higher than that in some countries.
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Angola, Mozambique and Tanzania experienced greater population declines than previously known, and elephants face local extinction in parts of the Democratic Republic of Congo, Cameroon and Zambia, the study said.
Results of the study were announced ahead of the International Union for the Conservation of Nature World Conservation Congress in Honolulu.
Allen, who provided USD 7 million for the effort, said he decided to launch the census after hearing three years ago that there had not been a comprehensive count of African elephants in decades.
"I took my first trip to Africa in 2006 and have been fascinated by elephants ever since," he said. "They are intelligent, expressive and dignified - but not to be underestimated. So, as this latest poaching crisis began escalating, I felt compelled to do something about it."
Its methodology involves manually counting animals while maintaining a specific altitude and following calibrated strips of land below the plane. The team also used video surveillance when counting big herds.