"Sadly, in 2009, we had a terrible drought, and we started seeing a lot of illegal killing of elephants as well as natural deaths," Wittemyer told Live Science. "We've been struggling to respond. We've been trying to find solutions to dampen the illegal killing."
His team used data on natural deaths versus poaching deaths in the Samburu National Reserve in Kenya, and then applied these numbers to a continent-wide database called MIKE, or Monitoring the Illegal Killing of Elephants. Started in 2002, MIKE is maintained by communities across Africa that report when, where and how elephants die.
The researchers created two computer models: one that looked at 12 MIKE sites with the best carcass data, and a second that examined all 306 sites, even those with less information about elephant deaths. The researchers did not include areas in West Africa, which is home to about 2 percent of the African elephant population, because data there are sparse, Wittemyer said.
In the past 10 years, elephant numbers at the 12 sites have decreased by 7 percent, which takes into account that elephant numbers were mostly increasing until 2009. Elephants in central Africa decreased by more than 60 percent in the past 10 years, according to an analysis of three locations in the 12-site model. Poaching is so widespread that 75 percent of elephant populations across the continent have been declining since 2009, with only 25 percent showing stable or increasing numbers, Wittemyer said.