When field rangers at the Phongolo Nature Reserve in northern KwaZulu-Natal told Ferdi Myburgh of the dead birds they had encountered while out on patrol, he and his team started putting “two and two together”.
The previous day, 8 November, had been sweltering, reaching an unusual 40°C by 10 am, topping 45°C by noon — and cooling only at sunset.
“The same day I noticed that in the troop of monkeys that live around the office, that one female and her baby had died due to the heat,” says Myburgh, the reserve’s conservation manager.
In total, rangers discovered about 60 dead birds of different species wherein areas they patrolled; people on neighbouring properties reported sightings of dead birds and bats.
“I found three yellow-fronted canaries tucked between a battery and a wall at an observation hide, where they tried to get away from the heat,” says Myburgh.
“What’s interesting is that there was water available 5m from where they died, so it’s not so much dehydration maybe, but heat-related stress that caused the deaths, but that is speculation on my side.”
Such high temperatures are not unheard of in Phongolo. “We have recorded 47°C, I believe, but it’s for a brief period in the day. This time around it was the duration of the heat more than anything else that caused these little animals to succumb.”
That dozens of birds and bats perished in one day of extreme heat in the region alarms Professor Andrew McKechnie of the University of Pretoria, who is the South African research chair in conservation physiology at the South African National Biodiversity Institute.
He runs a research programme studying the effects of climate change on birds and bats.
This bird and bat die-off, he says, seems to have been driven by the same processes as similar die-offs in Australia: lethal hyperthermia or dehydration.
“Essentially what happened on 8 November is that air temperatures in northern KwaZulu-Natal were about five degrees hotter than the previous day. It was just essentially that one extremely hot day,” he says. “From a bird physiology perspective, the challenges in terms of avoiding heatstroke become pronounced on days above 40°C.”
In recent years, McKechnie, together with his colleagues and students, has published several studies predicting that mass mortality events during heatwaves will become more common as climate change advances.
In Australia, says McKechnie, such die-offs have become relatively routine events. “This pattern of one or two extremely hot days during a longer period of more moderate weather seems to be quite a regular feature of these die-off,” he says.
The northern KwaZulu-Natal event is the first involving South African species of which he is aware, McKechnie says. “There were reports of strange drinking behaviour. Certainly, an unprecedented number of birds were coming down to pools of water to drink, to try to cool off — species that are normally completely independent of water.”
McKechnie strongly suspects that birds in more humid areas, such as KwaZulu-Natal, may be at similar or even greater risk of significant mortality events compared to the desert species that most of his work focuses on, because higher humidity makes it harder for them to offload heat under very hot conditions.
South Africa’s birds already face many immediate threats caused by human activities such as overfishing and powerline mortalities, says Mark Anderson, the chief executive of Birdlife South Africa.
Climate change, however, is a “more insidious threat” and requires the co-operation of a multitude of stakeholders, including the government and industry, Anderson says. “Although the KwaZulu-Natal event involved, as far as we can tell, only common species, if these events become more frequent in future as is being predicted, we could also face scenarios whereby massive damage is done to populations of threatened species in a matter of hours.”
Anderson says red larks in Australia are one example of a high-risk species. Another high-risk species, in KwaZulu-Natal, is the green barbet and if a heatwave of similar magnitude materialises a little further south, affecting the Ngoya Forest, it could be devastating for this species.
Vicky Kearney, a landowner in the neighbouring Pongola Game Reserve, rescued several overheated bats on her property on 8 November.
“It’s already very hot here, but it was ridiculously hot. We saw birds on the floor, and they were panting, so we put the sprinklers on and made a birdbath for them. The bats were so weak and disoriented that they were crashing into the windows and everything,” Kearney says.
“One was so weak he couldn’t keep his head up. We caught him and wrapped a towel around him and put him in some water to cool him down, and he was drinking from the tap. That’s how thirsty he was.”
Myburgh says, from 2013 to last year, on average there was one day between 1 and 17 November on which temperatures exceeded 40°C.
“By 17 November [this year], we had three events of over 40°C. What we’re worried about is that February is our hottest month and we’re technically only in spring. We don’t know if it’s just an outlier — that we’re already this hot this early in the season. This has been a very hot November,” Myburgh says.
“This is also one of the driest Novembers. It’s been a very dry November in a dry season so far; food is in short supply and then you see the animals get whacked by these high temperatures and dying of heat stress,” Myburgh adds.