Africa's savanna elephants could be wiped out, with their numbers falling rapidly, as ivory trades drive poaching across the continent, a study says.
The continent's savanna elephant population plummeted by about 30% from 2007 to 2014 and is declining at about 8% 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?" said elephant ecologist and lead researcher Mike Chase.
"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 planes to fly the equivalent of going to the moon and part of the way back.
The study, known as the Great Elephant Census and involving 90 scientists, estimated a population of 352,271 savanna elephants.
Researchers spotted about 12 carcasses for every 100 live elephants overall, indicating poaching at a level high enough to cause population decline.
But the rates were much higher than that in some countries.
Angola, Mozambique and Tanzania experienced greater population declines than previously known, and elephants face extinction in parts of the Democratic Republic of Congo, Cameroon and Zambia, said the study.
It also says numbers of elephants in South Africa, Uganda and parts of Malawi and Kenya were stable or partly increasing.
Results of the study were announced ahead of the International Union for the Conservation of Nature World Conservation Congress in Honolulu.
Mr Allen, who provided seven million dollars for the effort, said he launched 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."
The research team used the limited existing data as a baseline for the study. But this survey is more comprehensive and will serve as a more reliable baseline for future observations, the team said.
Its methodology involves manually counting animals while maintaining a specific altitude and following calibrated strips of land below the plane.
The method is widely used for surveying animals on large plots of land and was the most accurate method of three tested on a known population in Africa, said Mr Chase.
The team also used video surveillance when counting big herds.
Elephants are threatened by ivory trading, which is banned internationally, but the domestic trade of ivory within countries is legal nearly everywhere.
A motion being considered at the Hawaii conference seeks to change that by gaining international consensus to close all domestic ivory markets.
It noted that illegal killing of elephants for their tusks threatens national security, hinders economic development and endangers those tasked with protecting the animals.
US president Barack Obama and Chinese president Xi Jinping announced their commitment last year to combating wildlife trafficking.
The leaders promised to work toward a nearly complete ban on ivory imports and exports and an end to the domestic ivory trade.
Estimated density of savannah elephant populations produced by the Great Elephant Census (Chase et al 2016 in PeerJ) pic.twitter.com/TmeEx6oJrY— Gavin Masterson (@gavinprm) August 31, 2016
The decline in savanna elephants is tied directly to criminal poaching activities, some with links to terrorist groups, said Washington's non-profit Environmental Investigation Agency.
"Trade in ivory has been a driver of destabilization wherever it occurs in Africa," agency president Allan Thornton said.
One-time auctions of stockpiled ivory to China and Japan in 2008 resulted in a spike in illegal poaching, and the rate of decline among Africa's elephants has been accelerating since, said Mr Thornton.
In areas with a high rate of population decline, the savanna turns into an overgrown thicket devoid of grasslands that sustain other wildlife and becomes overrun by disease-carrying tsetse flies, said James Deutsch, director of Mr Allen's Vulcan Inc Wildlife Conservation.
And that land becomes useless for tourism when the elephants are removed, he said.