Elephants are dying in droves in Botswana. Scientists don’t know why

Die-offs of African elephants have once again erupted in Botswana. In just the first three months of 2021, 39 have succumbed.

The mysterious deaths occurred in the Moremi Game Reserve, in the northern part of the country, nearly 100 kilometers from a region of the Okavango Delta, where about 350 African elephants died during May and June in 2020. Puzzled scientists have been calling for thorough investigations as the government sends mixed messages on the cause of death.

Anthrax and bacterial infections had been ruled out in the new deaths and “further laboratory analysis is ongoing,” Botswana’s Department of Wildlife and National Parks reported in a March 24 news release.

However, the 39 recent deaths were linked, based on preliminary results, to the same cyanobacteria toxins blamed for last year’s mass die-off, said Philda Kereng, Botswana’s Minister of Environment, Natural Resources Conservation and Tourism, in a March 30 state television address.

Remote sensing of areas of last year’s mass die-off supports the cyanobacteria theory. From March through July 2020, cyanobacteria abundance increased continuously as water sources were shrinking, researchers report online May 28 in the Innovation. With climate change, bodies of water get warmer and toxic cyanobacteria thrive.

Other evidence points to a pathogen as well. “The 2021 elephant mortalities are again specific to elephants, as was the case in 2020,” says Shahan Azeem, a veterinary scientist at the University of Veterinary and Animal Sciences in Lahore, Pakistan.

If anthrax were to blame, other animals would have been affected, but they were not. And there would have been the telltale signs of bleeding on the carcasses, which was not the case. Poaching was also ruled out, because the elephants’ bodies were intact with their tusks. An investigation of the larger 2020 die-off suggests that a pathogen may have been the cause, Azeem and colleagues reported online August 5, 2020, in the African Journal of Wildlife Research.

Botswana and neighboring countries in southern Africa have a transboundary conservation agreement under which elephants can roam across borders during migration. As Botswana, home to about 130,000 African elephants, has struggled to explain the recent deaths, Zimbabwe on its eastern border reported the death of 37 elephants in 2020. Sudden deaths in one area concern the others. Scientists had first blamed the Zimbabwe deaths on hemorrhagic septicemia, a disease caused by the bacterium Pasteurella multocida.

But more recent genetic studies point to a related bacterium, Bisgaard Taxon 45, as the culprit, says Jessica Dawson, CEO of Victoria Falls Wildlife Trust in Zimbabwe, which has been doing lab analyses for that country’s deaths. 

In March, the International Union for Conservation of Nature called African forest elephants “critically endangered” and African savannah elephants “endangered.” The IUCN lists poaching as the principal threat along with a rapid increase in land use by humans, which has decreased and fragmented the elephants’ living areas.

Shrinking habitat and climate change may play a role in keeping the elephants exposed to the deadly pathogen — whatever it is, researchers say. The area is a hot spot for human-elephant conflict. Fencing to keep the animals away from crops and the deep Okavango River “imprison” the elephants, biologist Stuart Pimm of Duke University and colleagues wrote January 11 in PeerJ. The researchers tracked elephants in the area and showed very limited movement.

“What’s clear is that in Botswana, and indeed in other places, fences restrict those movements,” Pimm says. “Elephants can’t escape what may be a dangerous situation for them.”