In a Hotter World, Desert Birds Will Face a Much Higher Risk of Dehydration

(Author: Meghan Bartels, Photo: Sandrine Biziaux-Scherson, February 13, 2017)

As the climate changes, desert-dwelling birds are going to need more oases than ever to stay cool and hydrated, according to a new study.

When the mercury soars, birds don’t really sweat it—but only because they can’t. Instead of sweating, birds harness the cooling power of panting, which expels excess heat by evaporating water.

“They have their beaks open and you can see them heaving, their bodies are going up and down,” says Deborah Finch, a U.S. Forest Service biologist who has studied desert birds. “You know that they’re feeling overheated.”

But cooling off comes at a price: water loss. Birds need to replace that water, and finding juicy fruits, juicy bugs, or another water source to replenish their reserves takes serious effort. If they can’t find water, birds sometimes die in the heat—an event that could grow more common as climate change causes an increase in hot days and their severity in many places.

To better understand what these changes could mean for birds, Thomas Albright, a geographer and biologist at the University of Nevada, Reno, did the math to figure out how much heat birds can take. “We’re almost acting like accountants, balancing the water budgets of these birds,” he says. His team knew from previous studies that if a bird loses more than 15 percent of its body weight in water, it will likely die. But they wanted to see how much climate change birds can take before they hit that limit. Their research was published today in the Proceedings of the National Academy of Sciences.

With the birds’ safety in mind, Albright’s colleagues designed an experiment to estimate how quickly birds grow dehydrated at higher temperatures. The team caught about 200 birds of five different species common in southwestern U.S. deserts. Then they put each bird in a closed chamber that measures water loss and cranked up the temperature.

The scientists ended the test after each bird lost around 10 percent of its body mass, allowing it to recover quickly and stay healthy. They found that the smaller species in the study (Lesser Goldfinches and House Finches) burned through their water reserves more quickly than the larger birds (Cactus Wrens, Abert’s Towhees, and Curve-billed Thrashers). This makes sense: the smaller birds started with less water, so they used up their reserves sooner. Meanwhile, the larger birds had bigger stockpiles that could last longer.

The team then mapped the locations where these birds faced high risk of dehydration today, and simulated what would happen if those areas grew hotter, assuming a 7.2°F (4°C) across-the-board temperature rise by the end of the century. That’s on the high end of estimates produced by the Intergovernmental Panel on Climate Change, but served as a starting point to let them examine birds’ responses.

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