University of Illinois College of ACES
In a warming climate, can birds take the heat?
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[November 20, 2020]
We don’t know precisely how hot things will get as climate change
marches on, but there’s reason to believe animals in the tropics may
not fare as well as their temperate relatives. Many scientists think
tropical animals, because they’re accustomed to a more stable
thermal environment, may be pushed beyond their limits quickly as
temperatures soar. And that could lead to massive species loss.
Yet, in a first-of-its-kind study, University of Illinois
researchers show both temperate and tropical birds can handle acute
heat stress much better than expected.
“In terms of their thermal physiology, a lot of these birds,
including tropical species, can tolerate temperatures that are a lot
higher than what they experience in their daily lives. That was
surprising because tropical ectotherms, such as insects, have been
shown to be extremely vulnerable to climate warming,” says Henry
Pollock, postdoctoral researcher at Illinois and first author on the
study. “We're just not seeing the same things in birds. It is
somewhat encouraging.”
Although they observed some promising trends, the researchers
caution against celebrating too soon.
“It's not necessarily comforting 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 Jeff Brawn, professor in the
Department of Natural Resources and Environmental Sciences at
Illinois and co-author on the study. “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.”
To test the assumption that tropical and temperate birds differ in
their ability to cope with heat stress, Pollock brought 81 species
from Panama and South Carolina into field labs to test their
responses to rising temperatures. Using tiny sensors, he was able to
detect internal body temperatures, as well as metabolic rates, when
he exposed the birds to warmer and warmer environments.
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Species from both temperate and tropical zones handled the rising
temperatures just fine. Birds from South Carolina had a higher heat
tolerance, on average, than Panamanian birds, but both groups
exceeded Pollock and Brawn’s expectations. And among all the birds,
doves and pigeons emerged as thermal superstars. Most birds cool
down by panting, but doves and pigeons take advantage of their
unique-among-birds ability to “sweat.” In fact, Pollock says, they
exceeded the limits of his testing equipment.
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Although the study provided the first-ever heat tolerance data for many bird
species, the results take on more meaning when put into the context of warming
projections.
“Both temperate and tropical birds were able to tolerate temperatures into the
40s [in degrees Celsius], but they only experience maximum temperatures of
around 30 degrees Celsius in their everyday environments, so they have a
substantial buffer,” Pollock says.
In other words, even if maximum air temperatures rise 3 to 4 degrees Celsius, as
projected by some scientists, that’s well within the thermal safety margins of
all the birds Pollock measured.
![](http://archives.lincolndailynews.com/2020/Nov/20/images/ads/current/graue_preowned_111620.png)
It’s important to note the experiment, which measured acute heat stress, doesn’t
exactly replicate what’s projected to happen during much more gradual climate
warming. But few studies have examined the effects of chronic heat stress in
birds, and having this baseline knowledge of their acute physiological limits is
a good start.
“This is the first geographic comparison ever for birds. 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,” Pollock says.
Brawn adds, “We're just starting to scratch the surface of what we need to do to
really understand how climate change is going to affect birds. But this is an
important first step.”
The article, “Heat tolerances of temperate and tropical birds and their
implications for susceptibility to climate warming,” is published in Functional
Ecology [DOI: 10.1111/1365-2435.13693]. Authors include Henry Pollock, Jeff
Brawn, and Zachary Cheviron. The research was supported by the Smithsonian
Tropical Research Institute, the National Science Foundation, the U.S.
Department of Agriculture, and the University of Illinois Urbana-Champaign.
The Department of Natural Resources and Environmental Sciences is in the College
of Agricultural, Consumer and Environmental Sciences at the University of
Illinois.
[Sources: Henry Pollock
News writer: Lauren Quinn] |