The delays in testing could “literally be killing elephants,” Mr. Hiley added.
Dr. Mmadi Reuben, the principal veterinary officer at Botswana’s Department of Wildlife and National Parks, said the government is taking the deaths seriously and responded “swiftly, adequately and responsibly — as soon as we received this information.”
He said that some testing has ruled out common causes like anthrax, which is caused by bacteria that occur naturally in soil. He and his colleagues are now working with labs in Zimbabwe, South Africa and Canada to perform further testing. “It’s not going to be a one-off thing where we say, ‘We’ve sent out samples, now we’re done,’” Dr. Reuben said. “It’s an ongoing dialogue with different labs.”
There is still no evidence that the deaths are foul play by humans, he added.
Cyanide, which poachers sometimes use to poison elephants, seems unlikely, because carcasses tend to be clumped together near where the poison was deployed. It also tends to kill other animals, but no other species seem to be affected in this case. However, it’s possible that other poisons could be used against elephants, and Mr. Hiley says some of them can dissipate quickly.
Covid-19, he added, is unlikely, because the disease has yet to infect people in Okavango’s remote communities. There is also no evidence yet that elephants can contract the virus.
Dr. Thouless suspects that a naturally occurring disease is the most likely culprit. One leading candidate is encephalomyocarditis, a viral infection that can be transmitted by rodents, which can cause neurological symptoms. It killed around 60 elephants in South Africa’s Kruger National Park in the mid-1990s. Botswana also recently emerged from a drought, which could have left some elephants stressed and more vulnerable to disease, Dr. Thouless said.
At this point, he continued, the deaths do not constitute a conservation crisis, because the numbers documented so far represent a small percentage of the 15,000 to 20,000 elephants that live in the Okavango Panhandle. “This is distressing, but it’s currently trivial in population terms,” he said.
Past examples also show that when conditions are favorable, elephants can quickly rebound. For example, in 1970 and 1971, a drought in Tsavo East National Park in Kenya killed an estimated 5,900 of the park’s 35,000 elephants. By 1973, the population was back to 35,000.