Our Burning Planet

Survival of the coolest — Oppenheimer research grant winner on overheating birds in a changing climate

‘Black bulbs’ set up to log temperatures experienced by birds. (Photo: Supplied)

11 Oct 2024

Climate change biologist Dr Shannon Conradie, the winner of this year’s $150,000 Jennifer Ward Oppenheimer Research Grant, is fascinated by how animals interact with their habitats, and her studies focus on ‘understanding the relationship between complex changing environmental conditions and population survival and fitness in wildlife’.

Do birds take siestas in the desert? To survive they have to get out of the heat. But equally, to eat and drink they have to make forays into the furnace. Global warming is making this equation of eat, drink, snooze more fraught.

Many birds are finding conditions too hot to handle, and desert species are most at risk.

To survive, they need to hotfoot, or rather hotwing, it to where life is more tolerable, or find a way to get used to new extremes in temperature. Either way, they live in a state of constant trade-offs: how far can they fly to get water before they use up their energy; can they pant fast enough to keep cool; how long can they spend in the open before they have to retreat into the shade; can they find food close enough to keep healthy?

Climate change biologist Dr Shannon Conradie, the winner of this year’s $150,000 Jennifer Ward Oppenheimer Research Grant, is fascinated by how animals interact with their habitats, and her studies focus on “understanding the relationship between complex changing environmental conditions and population survival and fitness in wildlife”.

This quest for understanding is urgent. By the end of this century the maximum air temperatures in some desert zones will increase by up to 5°C, far beyond the upper limits of desert birds’ tolerance.

Conradie, who lectures at Wits University, says: “We know that if it is hot, birds are spending more energy and more water. At temperatures that are close to about 40°C, the birds start dumping off excess water to try and stay cool. And when they’re doing this, they’re at risk of lethal dehydration because they’re losing too much water. But if they don’t do that, they might risk hyperthermia.”

Climate change biologist Dr Shannon Conradie, winner of the 2024 JWO research grant. (Photo: Supplied)

birds heat Southern yellow-billed hornbills: when average summer temperatures breach 35°C, there's about a 50% drop off in breeding success. (Photo: Supplied)

The birds have limited options: “They can adjust their physiology or adjust their behaviour. In terms of physiology, if there is a continuous supply of drinking water, a bird can just lose more water because it can drink the water back and keep itself cool by evaporation and panting.

“What birds can also do is reduce their time spent in hot environments. If there are cooler sites, they’ll go and sit there. They will generally spread their wings to allow for wind to convectively cool them, and they’ll spend their time resting in the shade at the hottest time of day. But that also comes with trade-offs. When maximum daily temperatures are above 35°C, as a rule of thumb a lot of species are stopping their daily activities like foraging because they’re spending more time either in the shade or panting and then they’re not actually able to eat as much.

“So we have a tipping point where they’re not able to maintain body condition because they’re having to thermoregulate. And consecutive days of doing this is problematic because they’re losing body mass from not being able to forage.

“And we’re seeing knock-on effects of birds stopping breeding because it’s too hot and their body condition is too compromised. We’ve seen in southern yellow-billed hornbills, for example, when average summer temperatures are above 35°C, there’s about a 50% drop off in breeding success, because of these heat-related trade-offs that they have to make.”

And as if all this isn’t tricky enough, factor in a heatwave on top of that, and birds plummet from the skies, chicks jump out of nests in desperation, and the shock stunts biodiversity. A mass mortality of this nature occurred at the Pongola Nature Reserve in KwaZulu-Natal in November 2020, when temperatures hit 45°C, killing 110 birds and fruit bats in a very small area searched by rangers. Although the only one recorded in South Africa, such events have been more extensively chronicled in Australia.

Climate change biologist Dr Shannon Conradie. (Photo: Supplied)

Conradie will use her JWO grant to amass the evidence of the biological limitations of species distribution “in order to determine areas critical for conservation and management action”. The research grant scheme is managed by Oppenheimer Generations Research and Conservation and Oppenheimer Generations Philanthropies and was established six years ago to help early-career scientists develop scientific solutions to African problems. The announcement was made at the 13th Oppenheimer Research Conference in Midrand.

Conradie says she’s “always been a bit of a nature lover and enjoyed being outdoors, investigating how animals operate in their environments. That set me on the path of doing a degree in zoology. During my master’s I started looking at how species respond to climate. And then during my postdoc, I did some fieldwork in the Kalahari Desert which led to the questions that I’m asking now: how does habitat structure define the thermal environment that animals experience and how is that relationship changing? What makes species vulnerable to risks of climate change and habitat change?”

That field trip was to research the “energy and water balances of the white-browed sparrow-weaver (Plocepasser mahali). We did this through what we call a doubly labelled water technique. These birds roost in U-shaped nests, which have two entrances. So we captured them at night by gently waking them up in the nest. They would fly into bags and we would take a blood sample and then administer an isotopic water solution. We then let that circulate into their bloodstream, take a second blood sample, and we put them back into their nest.

“The next day, we spend the entire day observing that individual. These individuals have colourings on their legs so we can identify who we administered the treatment to. Then, 24 hours later, we recapture and take a third blood sample from that individual and you can measure the water that has been used up.

“This particular data set is still being analysed, and I’m also developing a technique called biophysical modelling, which uses physics and biology to predict water fluxes and energy fluxes in the environment. So, instead of having to go and capture these birds, we can predict it.”

This lies at the heart of the JWO grant research proposal.

“This project aims to use science-based, advanced technology and biophysical modelling to understand and predict species’ thermal vulnerabilities, breeding outcomes and population stability under global change across sub-Saharan Africa. The project will use cutting-edge technology for scenario modelling to determine how various combinations of global change drivers, such as land use and climate change, may impact species and population structures in terrestrial and freshwater systems.”

The project isn’t just looking at birds, says Conradie. “I want to look at bats, small mammals and reptiles, but using the bird data set as a training ground to see what we need to collect. Do we need to collect anything or can we actually use this predictive biophysical model and extrapolate it to other species? We’ll be using 15 years’ worth of data to build the predictive models and to see what the minimum amount of data is that we might need to collect and then to go out and collect that data for other species.”

‘Black bulbs’ set up to log temperatures experienced by birds. (Photo: Supplied)

The research will entail “gathering satellite climate data, but also weather station data and then data that we collect at a microclimate habitat, or microclimate level. We do that through what we call ‘black bulbs’, essentially two copper spheres which we paint matte black and glue together. In the middle of that is an ‘i-button’ that logs temperature, under a tree or in the sun.

“That fine-scale weather or climate that an animal would be experiencing in that exact location is the data we pull in to make these predictions, from arid environments like the Kalahari to coastal forests. We intend doing some work in woodland areas in Zambia and coastland forests in KwaZulu-Natal, and maybe Mozambique.

“The idea is to map the thermal environment using satellite imagery and drones and then to categorise the microclimates with the smaller black bulb loggers. Then we can expand those models across landscapes, even across continents.

Conradie says that “arid zones are at the edge of animals’ thermal vulnerability generally, and we are seeing that these areas are warming quite rapidly. In the last 10 years the Kalahari has warmed by 2°C. We know a lot about the temperature warming, but what we know less about is how things like humidity are going to play a role, because dry heat is one thing, but when you’re in a hot and humid environment, it’s different.

“We also know that the African continent as a whole is warming about one-and-a-half times more rapidly than the global average.”

Conradie says there is still a slim margin of error for animals in arid zones “but they’re definitely under more and more pressure. There is scope to adapt, but it depends on how quickly they’re able to do that.”

But there are glimmers of hope.

“One thing we know is species like the forktail drongos and pied crows are doing really well. They don’t seem to be struggling as much with these increases. They seem to be doing perfectly fine. But then we have species like the hornbills which we can see are struggling.”

Conradie hopes that identifying the physical features in the landscape that can help animals stay cool, and develop models of thermal vulnerability, will help conservation initiatives.

“If you’re a bird and you’re getting hot you could move under a tree to try and stay cool. But it depends if that tree is available or not. The idea is to look at habitat structure to see if the tree is available there or not. Then we can put in place conservation strategies to make sure we’re preserving those trees or water sources that are there to keep species cool.”

Conradie and her colleagues have noted that among birds that suffer the most from extreme heat are small songbirds, which cannot pant fast enough to stay cool. She hopes her research will allow their music to play on. DM

Yves Vanderhaeghen writes for Jive Media Africa, science communication partner of Oppenheimer Generations Research and Conservation (OGRC).

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