Despite multiple climate models from international researchers around the world, it remains uncertain how hot the world will be years from now. Some experts are especially concerned about tropical species who may not be able to survive warmer temperatures above their limit, resulting in a massive loss of tropical biodiversity.
In a unique study, researchers from the University of Illinois reveal the heat tolerance of tropical birds and susceptibility to global warming. The findings were recently published in the journal Functional Ecology describing how birds can handle acute levels of heat stress.
"Characterizing heat tolerance is critical for predicting an organism's vulnerability to climate warming," wrote the authors. Several studies have also concluded that global warming will affect tropical regions greater than others.
Heat Tolerance of Birds
For the study, the team measured the thermoregulatory responses to acute heat stress of 81 bird species. 58 species were tropical while the rest were temperate species.
In the laboratories, sensors detected internal body temperature and metabolic rates as the birds were exposed to different warm environments. While temperate species from South Caroline had significantly higher heat tolerance limits, tropical species from Panama were able to cope with rising temperatures better than expected. Henry Pollock explained that a lot of the bird species "can tolerate temperatures that are a lot higher than what they experience in their daily lives."
The birds with the highest thermal tolerance were doves and pigeons. While most bird species cool down by panting similar to dogs, doves and pigeons have their own way of sweating to cool their bodies. The two species were even able to exceed the limits of the equipment, shared Pollock.
He continued by saying that all species could tolerate temperatures above 104°F (40°C), but they only experience around 80°F in their natural habitats. The birds would be able to survive the anticipated increase of 37°F to 39°F in global temperatures.
Limitations of the experiments, noted the authors, is that the increased temperatures in a laboratory setting are only one factor of climate change in the real world. For now, the study is a good baseline to understand the effect of thermal heating on bird species.
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Indirect Effects of Climate Change
The results were surprising, Pollock said because ectotherms (i.e. bugs) are typically vulnerable to climate change. Ectotherms are animal species that rely on external sources of heating such as sunlight or warm water.
However, this is not comforting news, said Jeff Brawn. Just because tropical birds can tolerate warmer temperatures does not mean that they will be unaffected by climate change. Warming would most likely affect the birds indirectly, Brawn explained. "They may not be flying around panting [and] suffering from heat exhaustion," but may lose their natural habitat from drought, fires, land-clearing, or other climate change-related events.
Both Pollock and Brawn acknowledged the study as important initial steps to understanding how climate change will affect birds. "We need more data from more sites and studies of chronic heat stress over longer periods of time," said Pollock, but for now, it's a slight relief to know that tropical birds will be able to tolerate higher temperatures better than expected.
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