The number of savanna elephants in Africa is dramatically declining and the majestic animals are in danger of being wiped out, largely due to poaching, the results of a three-year aerial survey have revealed.

The continent's savanna elephant population plunged by about 30 percent from 2007 to 2014, and is declining at about 8 percent a year, according to the Great Elephant Census, published on Wednesday.

"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 aerial survey covered 18 countries using dozens of airplanes to fly the equivalent of going to the Moon and partway back.

The study, which was funded by Microsoft co-founder and philanthropist Paul Allen, estimated the population of savanna elephants at 352,271.

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 differed from country to country.

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, according to the study.

However, populations were found to be stable, or even increasing, in South Africa, Botswana, Uganda, parts of Kenya, Zambia, Zimbabwe, Malawi and the W-Arli-Pendjari conservation area that spans the borders of Benin, Niger and Burkina Faso.

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Results of the study, which involved 90 scientists, were announced before the International Union for the Conservation of Nature World Conservation Congress in Honolulu.

Allen, who provided $7m 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."