Can birds endure the warmth in a warming local weather?

We don't know exactly how hot things will get as climate change progresses, but there is reason to believe that animals in the tropics may not do as well as their temperate relatives. Many scientists believe that because tropical animals are used to a more stable thermal environment, they can quickly go beyond their limits as temperatures rise. And that could lead to massive species loss.

In a unique study, researchers from the University of Illinois show that both temperate and tropical birds can cope with acute heat stress much better than expected.

“In terms of their thermal physiology, many of these birds, including tropical species, can tolerate temperatures much higher than what they experience in their daily life. That was surprising, because tropical ectotherms like insects have been shown to be extremely vulnerable to global warming, ”says Henry Pollock, postdoctoral fellow in Illinois and lead author of the study. "We just don't see the same things in birds. It's a little encouraging."

Although they saw some promising trends, researchers caution against partying too soon.

Bronze-tailed Plumeleteer, Panama, Copyright Trevor Ellery, from the Surfbirds Galleries

"It's not exactly comforting news. If someone walks away from this thinking tropical bird, they'll be fine because they're not overheating. That would be a simplistic conclusion to remove this paper," said Jeff Brawn, professor in the Department of Natural Resources and Environmental Sciences in Illinois, and co-author of the study, "Warming is likely to have an indirect impact on tropical birds by affecting their resources and the structure of tropical forests. They may not fly around panting and suffer from heat exhaustion, but it does can have more indirect effects. "

To test the assumption that tropical and temperate birds differ in their ability to deal with heat stress, Pollock brought 81 species from Panama and South Carolina to field laboratories to test their responses to rising temperatures. With tiny sensors, he was able to record internal body temperatures and metabolic rates when he exposed the birds to warmer and warmer environments.

Species from temperate and tropical zones have coped well with rising temperatures. South Carolina birds, on average, had a higher heat tolerance than Panamanian birds, but both groups exceeded Pollock and Brawn's expectations. And among all birds, pigeons and pigeons appeared as thermal superstars. Most birds cool off with gasps, but pigeons and doves make use of their unique ability to "sweat" among birds. According to Pollock, they have even exceeded the limits of his test equipment.

Although the study provided the first heat tolerance data for many bird species, the findings related to warming projections are gaining importance.

"Both temperate and tropical birds could tolerate temperatures well into the 1940s [in degrees Celsius], but they only experience maximum temperatures of around 30 degrees Celsius in their daily environment, so they have a significant buffer," says Pollock.

In other words, even if the maximum air temperatures, as predicted by some scientists, rise by 3 to 4 degrees Celsius, this is within the thermal safety limits of all birds measured by Pollock.

It is important to note that the experiment that measured acute heat stress does not exactly reflect what is expected during a much more gradual global warming. Few studies have examined the effects of chronic heat stress in birds, and this basic knowledge of its acute physiological limits is a good place to start.

“This is the first geographic comparison for birds. We need more data from more locations and studies on chronic heat stress over longer periods of time. But at least I think what we can say is that they can tolerate higher temperatures than I think anyone expected, ”says Pollock.

Brawn adds, "We are only just beginning to scratch the surface of what we need to do to truly understand how climate change will affect birds, but this is an important first step."

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