Climate change is testing the resilience of our planet's birds. While tropical avian species appear especially vulnerable to habitat loss, drought, natural disasters, and declining prey, new research suggests they can withstand heat waves quite well.
Using the largest dataset of its kind, the research calls into question a commonly-held conclusion that tropical birds, living in grasslands, deserts, and mountains, are more vulnerable to climate warming than those living in more temperate climates.
Testing the heat tolerance of 81 bird species, 23 from one temperate site and 58 from another tropical site, researchers found both groups handled rising temperatures just fine.?
While it's true birds from more temperate areas are, on average, better at withstanding higher temperatures, their vulnerability to climate warming did not differ from their tropical cohorts.
Even if temperatures rose 3 or 4 degrees Celsius, researchers say that's well within the margin of safety for all the birds measured. In fact, virtually every species could withstand a temperature increase of 10 degrees Celsius and more.?
"Both temperate and tropical birds were able to tolerate temperatures into the 40s [in degrees Celsius] (starting around 104 degrees Fahrenheit), but they only experience maximum temperatures of around 30 degrees Celsius in their everyday environments, so they have a substantial buffer," says ecophysiologist Henry Pollock from the University of Illinois Urbana‐Champaign.
When things began to heat up, the team found that doves and pigeons, which are found in both temperate and tropical regions alike, stayed particularly cool.
In general, most birds tend to 'run hot', which is why scientists are worried about their future in a warming world. While many avian species rely on fluttering to reduce their body temperature – akin to dogs' panting –?that's a relatively energy-intensive strategy.
Even when the heat of the day rises as high as 60 degrees Celsius, some prior research suggests doves can maintain body temperatures 14 degrees Celsius below air temperature. Like pigeons, doves can beat the heat by passively 'sweating', allowing water to evaporate along the skin. Like fluttering, this requires a fair bit of energy.
But doves' sweating also requires a steady supply of water, and many parts of the world are facing more frequent and intense droughts with climate change. Which brings us to the bad news.
"If someone walked away from this thinking tropical birds are going to do fine because they're not going to overheat, that would be a simplistic bottom line to take away from this paper," says avian ecologist Jeff Brawn from the University of Illinois.?
"Warming is likely to affect tropical birds indirectly, by impacting their resources, the structure of tropical forests. So they may not be flying around panting, suffering from heat exhaustion, but there may be more indirect effects."
Like dehydration or starvation. While warm-blood creatures, like birds, may show remarkably high heat resistance, scientists worry that rapidly warming temperatures will drive much of their cold-blooded prey into decline.
It's also important to keep in mind the limitations of this research. The study was based on birds from just two locations, one in South Carolina and the other in Panama, and researchers only measured responses to acute heat stress, not chronic rising temperatures.
Future research will need to verify whether avian heat resistance stands for other locations, habitats, and conditions, especially because these results are unexpected.
Prior studies estimate 15 percent of bird and mammal species are already experiencing temperatures beyond their thermal safety margins, and while the authors of the current study pin this down to differences in methodology, the mixed results call for further verification.
"This is the first geographic comparison ever for birds," Pollock says.
"We need more data from more sites and studies of chronic heat stress over longer periods of time. But I think at the very least, what we can say is that they're able to tolerate higher temperatures than I think anybody expected."
The study was published in Functional Ecology.