Africa's elephant population has plunged faster than almost anyone predicted, raising startling questions about the failure to protect one of the world's largest mammals.
There are now only 352,271 savanna elephants in nearly all of sub-Saharan Africa, according to Elephants Without Borders, a research organisation that just completed an 18-country census.
Between 2007 and 2014, the elephant population declined by at least 30 per cent, or 144,000 elephants, the study found.
Previous estimates had suggested that the population was considerably higher, making the results of the new study, called the Great Elephant Census, a devastating revelation.
"These dramatic declines in elephant populations are almost certainly due to poaching for ivory," the study said.
"Elephant poaching has increased substantially over the past 5-10 years, especially in eastern and western Africa."
The researchers delivered their findings after years of travel across Africa in helicopters and bush planes, spending about 10,000 hours in the air. National Geographic called the study "the largest wildlife census in history". Some of the countries included, such as Angola, had never before been surveyed.
"If we can't save the African elephant, what is the hope of conserving the rest of Africa's wildlife?" said Mike Chase, the principal investigator in the census and the founder of Elephants Without Borders.
The population of savanna elephants declined dramatically as their land was destroyed. Their range "shrank from three million square miles in 1979 to just over one million square miles in 2007," according to the World Wildlife Fund.
In recent decades, poaching has added a devastating new threat.
Most of the ivory taken from elephants ends up in Asia, where it fetches as much as US$1000 per pound and is frequently used in unproven medicinal treatments.
As the Great Elephant Census researchers flew over much of Africa, they repeatedly saw the detritus of the poachers' trade - large elephant carcasses left to rot in the sun.
"Dead elephants remain visible for several years after dying," the study notes.
Some countries were hit harder than others. In Cameroon, researchers found nearly as many dead elephants as live ones.
"Of note, Angola, Mozambique and Tanzania's elephants experienced staggering population declines, which were much greater than previously known and expected," researchers said.
The study, which was funded largely by billionaire Microsoft co-founder Paul Allen, revealed that Tanzania's elephant population declined by 53 per cent between 2009 and 2015, from about 109,000 in 2009 to 51,000 in 2015.
"We anticipated the decline, but not at this level," Edward Kohi, principal researcher for the Tanzania Wildlife Research Institute, told National Geographic.
Many African nations have attempted to boost their conservation efforts, particularly through the creation of anti-poaching units deployed to national parks, savannas and forests.
Earlier this year, Kenya set fire to 105 tonnes of ivory, an attempt to prove, in the words of President Uhuru Kenyatta, that "for us, ivory is worthless unless it is on our elephants". The United States recently announced a near-total ban on the ivory trade.
But for all the attention that poaching - and the subsequent decline in elephants - has received, there's no sign that it will stop anytime soon. On much of the continent, desperately poor poachers are paid far more than they would earn otherwise to target elephants and rhinos. If they are caught, which is relatively rare, they often serve short jail sentences.