Delays in testing could “literally be killing elephants,” Hiley added.
Dr. Mmadi Reuben, the chief veterinary officer for the Botswana Department of Wildlife and National Parks, said the government is taking the deaths seriously and responded “promptly, appropriately and responsibly, as soon as we receive this information.”
He said some tests have ruled out common causes like anthrax, which is caused by bacteria that occur naturally in the soil. He and his colleagues are now working with laboratories in Zimbabwe, South Africa, and Canada to conduct further tests. “It won’t be a one-time thing when we say, ‘We have sent samples, now we are done,'” said Dr. Reuben. “It is an ongoing dialogue with different laboratories.”
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 cluster near where the poison spread. It also tends to kill other animals, but no other species seems to be affected in this case. However, it is possible that other poisons may be used against elephants, and Mr. Hiley says that some of them can quickly dissipate.
Covid-19, he added, is unlikely, because the disease has not yet infected people in remote Okavango communities. There is also no evidence that elephants can contract the virus.
Dr. Thouless suspects that a natural disease is the most likely culprit. One of the main candidates is encephalomyocarditis, a viral infection that can be transmitted by rodents and that can cause neurological symptoms. It killed about 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 living in the Okavango Panhandle. “This is distressing, but it is currently trivial in terms of population,” he said.
The examples above also show that when conditions are favorable, elephants can recover quickly. For example, in 1970 and 1971, a drought in Tsavo East National Park in Kenya killed approximately 5,900 of the park’s 35,000 elephants. By 1973, the population had returned to 35,000.
