UC Berkeley researchers found that about 30 percent of bird populations in the Mojave Desert are declining due to direct, physiological responses to climate change.
According to lead author and campus postdoctoral researcher Eric Riddell, the increase in global temperature by 2 degrees Celsius has affected the ability of birds to retain enough water.
“As ecologists (or) biologists, we often think about how animals are going to experience some sort of lethal condition in the next century,” Riddell said. “The climate change that has already occurred is too much for these desert birds.”
According to Steven Beissinger, a campus professor of conservation biology and senior author of the study, birds need extra water to stay cool, which is called a “cooling cost.” Their ability to survive largely depends on whether or not that extra water is available. He added that birds also spread their wings to cool down, as this helps water evaporate.
The researchers worked with the findings of the UC Berkeley Museum of Vertebrate Zoology to test the effect of temperature changes on 50 different desert bird species. According to Riddell, the program identified which birds would struggle the most with water retention in the heat — these birds are the same ones to decline in population in the Mojave Desert.
The recent research was kicked off by findings from the Grinnell Resurvey Project, which documented the distribution of mammals and birds in California from the 1900s to the 1940s. The project was produced by Joseph Grinnell, the founding director of the Museum of Vertebrate Zoology. Using field notes from the museum, Beissinger’s team recorded the new distribution of birds and found a 30 percent decline in desert bird species.
The simulation tested specific species of Mojave Desert birds and their responses to temperature changes, according to Riddell.
“(It) took thousands of measurements to estimate how hot each species gets in the desert, how much sunlight their feathers absorb, the dimensions of the bird, how deep, how thick their feathers are,” Riddell said.
He added that the measurements helped pinpoint the specific ways various types of birds lost water and which birds were affected the most.
Insectivores, seed-eaters and carnivorous birds are more likely to lose water because of their diets, according to Riddell. These birds, now on the decline, include the American kestrel, the prairie falcon and the turkey vulture.
To Beissinger, the study is significant because of its unique contribution to climate change research.
Most research so far, he said, observes impacts on food webs and chains rather specific physical changes within populations. He added that there had previously been little evidence to suggest that changes in precipitation and temperature might affect a species’ ability to survive.
“This is one of the first, few studies that show direct physiological effects,” Beissinger said.