The bodies of numerous bee-eaters (above) and swallows who had migrated from the Northern Hemisphere were found around the country. (Supplied)
The annual spectacle of migratory birds arriving in South Africa in spring took a tragic turn this year when numerous bee-eaters and swallows perished during the cold snap at the end of October.
According to BirdLife South Africa, unpredictable and extreme weather conditions, including sub-zero temperatures, hail, heavy rains, awaited the avian travellers after their long and difficult journeys from the Northern Hemisphere.
The underlying causes are complex and “deeply worrisome”. Birds face various difficulties during their epic journeys, which is worsened by extreme weather and resource scarcity.
“This serves as a warning about the impact of climate change on declining migratory bird populations, and the need to understand the effect of more frequent extreme weather events.”
The non-profit warned that the annual spectacle of bird migration, which is one of nature’s incredible phenomena, is under threat because a “changing climate wreaks havoc on migratory birds”.
“We’ve received reports of numbers between two to 60 swallows dead in one location and two to 42 bee-eaters in another,” said Jessica Wilmot, the flyway and migrants project manager for BirdLife South Africa. “People have reported but there’s still lots unaccounted for.
“You don’t expect this volume of mortalities. While this isn’t the first time this event has occurred, its frequency is increasing and with additional threats faced by migratory birds, it’s a concern.”
Wilmot said the birds wouldn’t have had time to recover from their thousands of kilometres journey from Europe and Asia to escape their native home range winter. “And who knows what type of threats they faced along the way.”
Key stop-over sites, which they need to rest and refuel, “may be degraded so they are not gaining enough strength to survive and have the strength to withstand such a cold spell”.
Migratory birds are becoming more susceptible to environmental stressors because they cannot get sufficient high-quality resources necessary for replenishing their energy levels. And the accumulation of toxins undoubtedly weakens their immune systems, although this is not yet fully understood.
A similar incident in the United States a few years ago saw tragedy on an even greater scale, when migratory birds, forced to flee raging wildfires and seek refuge in areas with inadequate resources, were met with an unexpected snowstorm, resulting in the loss of thousands of birds.
“Subsequent scientific studies revealed this phenomenon as ‘weather whiplash’ … which was the root cause of this devastating migratory bird mortality. These reports sound a stark warning about the cumulative impact of climate change on migratory birds, a group already in decline. The consequences are all too clear, highlighting the urgency of addressing this crisis,” BirdLife South Africa noted.
While human-caused climate warming is driving the increase of extreme climate events globally, the ecological cascading effects of these events as a severe threat to the conservation of migratory birds “have largely been understudied”, it said.
Andrew McKechnie, a professor in the department of zoology and entomology at the University of Pretoria, said a combination of factors probably caused the bird mortalities.
They would have been in a very poor body condition after recently arriving from their long migration. “These long migrations from one hemisphere to another really take it out of birds and they often arrive in really poor body condition.
“They would likely have burnt up all of their fat; they would probably be metabolising protein as well and so by the time they got here, they were just not in good condition,” said McKechnie, who is the South African Research Chair in Conservation Physiology at the South African National Biodiversity Institute.
“You combine that poor body condition with cold weather where your energy requirements go up to keep warm, but your energy supply goes down because all of those birds were aerial insectivores so they … feed on aerial insects and the moment you get this cold, your flying insects just vanish.”
This combination of high energy requirements because of the cold, the rain and the wind, and low energy supply because the cold weather would have pushed out the insect availability, “was just a recipe for disaster”.
McKechnie is also the co-principal investigator of the Hot Birds Research Project, which
studies the behaviour and physiology of desert birds to understand and predict their responses to climate change.
In a scientific paper with colleagues in 2021, he and his colleagues documented the first heat-related mortality event involving wild birds and bats in Southern Africa. On 8 November 2020, about 50 birds and 60 bats were found dead in northern KwaZulu‐Natal after temperatures of 43°C to 45°C, although these probably represented only a fraction of mortalities.
“This mortality event occurred on a single very hot day preceded by several cooler days … and involved weather conditions similar to those associated with at least one recent flying‐fox die‐off in Australia,” they wrote.
McKechnie told the Mail & Guardian this week that extreme weather events have been happening for a long time. “I have seen predictions that climate change, if it causes more variability in weather, can result in more extreme cold weather as well.
“I’m not a climate scientist and I would be very hesitant to ascribe that cold period directly to climate change and I don’t think we can necessarily do that, but I think it just speaks to the vulnerability of birds to these extreme weather events, whether it’s cold or heat.”
As the reports came in of common species such as the barn swallows and bee-eaters dropping dead in the cold spell, “you also have to wonder about the more threatened species”, he said, citing the example of blue swallows, which are down to just 30 pairs in KwaZulu-Natal.
“It’s one thing for these common species, but it’s another matter altogether when you’ve got really threatened species and a small breeding population.”
In circumstances such as this, “it’s not beyond possibility that an entire population can be wiped out by an extreme event”, McKechnie said.
BirdLife South Africa said extreme weather events are predicted to become more common and information about bird mortalities “will help us predict how birds will be affected and identify particularly vulnerable species. Consequently, documenting the extent of these events is vital”.
*If you encountered dead birds in the aftermath of the cold snap, forward the relevant information to Jessica Wilmot: [email protected]