Flock Of Red-billed Quelea (Quelea quelea) At Sunset Flying To Roosting Tree. (Photo by Wolfgang Kaehler/LightRocket via Getty Images)
Birds living in hot, humid climates have evolved to handle larger spikes in body temperature surprisingly better than their counterparts in deserts or cool mountains, according to new research led by the University of Pretoria.
The study, which is based on the PhD work of zoology student Marc Freeman, found that rising temperatures because of climate change will affect bird species differently. Their abilities to withstand extremely hot conditions depends on the part of the world that they find themselves in and the climatic region to which their physiology has become adapted over thousands of years.
The team of ornithologists collected data from 53 bird species in South Africa, including from Richards Bay, Harrismith and desert areas in the Northern Cape, which experience different air temperatures and levels of humidity.
They discovered that red-billed queleas are able to withstand body temperatures up to 48°C, which was the highest temperature measured. Burchell’s starlings, on the other hand, can handle 43°C before showing signs of severe heat stress. For the maximum air temperatures that the various species could handle, heat tolerance limits ranged from 43.3°C to 56°C.
The university’s ornithologists are involved in the international Hot Birds Research Project, which studies the behaviour and physiology of desert birds to understand and predict their responses to climate change.
What surprised the researchers is that bird species living in humid lowland sites, and not desert birds, were able to withstand higher body temperature extremes and could tolerate hyperthermia better, before experiencing difficulty moving and could no longer safely regulate their body temperatures.
“Birds living in hot deserts don’t seem to have the same capacity for hyperthermia as birds from cooler environments and East Coast environments,” said Andrew McKechnie, of the department of zoology and entomology and South African Research Chair in Conservation Physiology, and lead researcher, told Mail & Guardian. “The thing is that hyperthermia and letting your body temperature go quite far above normal levels is a really good way to save water.”
Water conservation, said McKechnie, who is also the co-principal investigator of the Hot Birds Research Project, has always been recognised as one of the important functions of hyperthermia. “And if there’s an environment where you would expect strong selections for water conservation, it’s deserts. So, I was really surprised that birds in deserts don’t seem to be able to let their body temperatures go as high as birds from other environments.”
The ability of birds from lowland areas to better handle hyperthermia is their internal body temperatures are able to rise higher and have a lower resting body temperature than birds from other regions. Humid conditions are typically difficult to handle when combined with hot weather.
According to McKechnie, it’s important to know just how much heat birds and other animals can stand before their bodies start shutting down on an extremely hot day. “Knowing this will help us to make better predictions about how vulnerable they are to higher temperatures and more frequent and intense heatwaves, whether such extreme events might be lethal to them, and under which conditions and at which temperatures we might see them dying on a large scale in future.”
Climate change is “relentless and ongoing” and the habitats in which birds live are heating up, he said. “In hot environments, many species already live life on the edge and can give us early warning of the impacts of change. We are studying the capacity of these birds to tolerate elevated body temperatures, and how this capacity varies among species.”
Each bird species has a particular resting body temperature and a maximum threshold to which their internal body temperatures can increase before their activity levels and bodily function is affected. Once the threshold is reached, overheating as a result of hyperthermia and subsequent heat exhaustion can prove fatal.
Lethal heatwaves have become increasingly common worldwide. In Australia, such events have caused the deaths of birds and fruit bats en masse. In 2018, a third of the country’s population of spectacled flying foxes — a type of fruit bat — died over the course of two extremely hot and humid days.
In November 2020, the first such event in South Africa was recorded around Pongola in northern KwaZulu-Natal on a humid day when temperatures quickly reached 45°C. “Twelve species of birds, including blue waxbills, fork-tailed drongos, magpie shrikes and yellow-fronted canaries, died, as well as 50 Wahlberg’s epauletted fruit bats,” McKechnie said.
This month, hundreds of baby swifts in southern Spain died after leaving their nests prematurely, when they tried to escape the extreme temperatures during one of the country’s earliest heatwaves on record, The Guardian reported.
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