Here’s how 53 African bird species are adapting to historic heat

Here’s how 53 African bird species are adapting to historic heat
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This article was originally featured on The Conversation.

During the northern hemisphere summer of 2022, yet another round of extreme heat waves roasted Eurasia, North America and northern Africa – a stark reminder that these conditions are becoming the new normal.

These events can have a severe impact on wildlife. For instance, reports of large-scale deaths of birds have become regular in recent years, as we’ve seen in Patagonia, Argentina and Spain.

These events highlight the need to understand how birds and other animals can withstand extreme heat. This information is essential to predict where and when future deaths could occur. It can also help us predict which species will be most affected.

Intriguingly, when we conducted a study to measure how much heat 53 bird species in southern Africa could stand, we found that species vary greatly in the way they handle heat.

Most importantly, the maximum temperature at which a bird’s body can get – what we refer to as “maximum tolerateable body temperature”) – varies among bird species from different climates. This means that birds from different climates will respond differently to extreme heat.

This important finding is important. Previous research assumed that the body temperature response to extreme air temperatures for birds was similar between species. This thinking has been used to predict how vulnerable birds will be to climate change.

Our study shows that reality is more complicated. The reality is more complex. Birds could have evolved differently depending on where they lived. This could have led to variations in body temperature and heat handling abilities.

Presuming that all birds handle heat the same way could lead to predictions that aren’t accurate. This could make it difficult for them to assess how vulnerable they really are to global warming. The body temperature limits for specific species are needed to improve the accuracy of such predictions.

Body temperature regulation in the heat

Our study examined 53 bird species from hot arid, cool mountainous or warm humid coastal regions of southern Africa.

We hypothesized that birds from different climates would have different body temperatures in response to extreme temperatures. This hypothesis was tested by measuring the birds’ body temperature and metabolic rate, as well as their evaporative water loss at increasing temperatures. (Water loss occurs when birds don’t wear pants and allow their bodies to cool down. )

We were particularly interested to know the maximum body temperature of the birds. This was taken just before birds began to show symptoms like loss of coordination and uncontrolled rises in body temperature. These symptoms are often associated with severe hyperthermia or overheating.

We found that desert birds comfortably handled air temperatures exceeding 50degC, without a dramatic increase in their body temperature. They maintained body temperatures below approximately 44.5degC.

In contrast, birds from warmer, humid regions tolerated air temperatures in the upper 40s before showing signs of severe hyperthermia. Their body temperatures increased on average by almost six degrees above normal levels of 38-41degC.

Generally, high temperatures in birds exposed to extreme heat can indicate that they aren’t capable of maintaining (or thermoregulating) optimal body temperatures.

However one species, the red-billed quelea, which occurs across much of sub-Saharan Africa, could cope with a body temperature increase to an astounding 48degC without any ill effect. This was previously considered physiologically impossible for birds.

Evolution of heat tolerance

Why did birds develop tolerance for such high body temperatures and are they still able to survive?

We believe that birds from more humid regions have learned to rely less upon evaporative cooling in hot weather.

Evaporative cool is when a bird loses heat through its mouth, or other means. It is the only way that a bird can heat off its surroundings if the temperature is higher than its own body temperature. Being able to tolerate high body temperatures allows birds to survive in humid areas where they can’t lose heat as much by panting.

Birds that have evolved in humid climates can survive extreme heat by allowing themselves to be hyperthermic. Desert birds, on the other hand, use highly efficient evaporative cooling to avoid hyperthermia.

This suggests that birds from different climates have evolved different body temperatures and heat tolerances.

Protecting birds from heat

Our study is highly relevant to understanding the dangers posed by extreme heat waves for birds and other wildlife. For instance, our findings confirm previous suspicions that songbirds, which make up over half of all bird species on Earth, are particularly vulnerable to heatwaves.

It is vital to develop strategies to reduce the impact of extreme heat events on birds and wildlife, as they are becoming more frequent and widespread in southern Africa. They are a growing threat to the region’s amazing biodiversity.

These risks were dramatically illustrated in northern KwaZulu-Natal, South Africa, on 8 November 2020, when air temperatures in the Pongola area soared to 45degC by mid-afternoon. This caused huge numbers of birds to succumb. Approximately 90% of the bird carcasses found by field rangers in the nearby Phongolo Nature Reserve in the aftermath of the heat were those of songbirds.

Managing protected areas can reduce the chance of future mortality events. For example, shady vegetation provides cool areas where birds can escape the heat. The likelihood of birds being able to keep their body temperatures below the lethal limit will increase if there are water sources available.

However, the only way to stop large-scale loss of avian biodiversity due to rapid global warming is rapid decarbonisation and a global shift to renewable energy sources.

Marc Trevor Freeman is awarded funding from the National Research Foundation.

Andrew McKechnie is funded by the National Research Foundation. He is the South African Research Chair for Conservation Physiology hosted by the South African National Biodiversity Institute. It is co-hosted at the University of Pretoria.

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