Silent Spring 2

Will birds go extinct? Study reveals the impact of climate change

Meanwhile, small mammals employ a survival technique used since the age of the dinosaurs.

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When it comes to environmental disasters, birds are literal canaries in the coal mine. The state of their existence can indicate when something is going very wrong with nature overall.

In the 1962 book Silent Spring, author Rachel Carson's investigative research revealed birds were dying in large numbers because of the pesticide DDT. Recent research suggests we may be undergoing a second Silent Spring, with record declines in bird species due to climate change.

A new study corroborates this research, predicting a potentially sad future for the survival of birds. Published Thursday in the journal Science, the study compares modern-day research regarding birds and small mammals to data gathered a century ago in the Mojave Desert.

The paper found surprising differences in the way both types of animals responded to climate change, ultimately concluding "birds declined markedly in response to warming and drying" of the desert. Small mammals, meanwhile, can use a technique that helped ancient small mammals survive when many dinosaurs perished — they can hide.

"Many of the desert birds that bird enthusiasts love to see will become more difficult to find, leaving the desert a quieter environment without birds," Eric Riddell, a corresponding author on the study and an assistant professor in the ecology department at Iowa State University, tells Inverse.

Violet–green swallow, a desert animal surveyed in the study.

Credit: Sean Peterson

How they did it — The researchers compared 34 small mammal species, including rodents, and 134 bird species at dozens of sites across the Mojave Desert and Joshua Tree National Park.

In order to observe how these two groupings of animals responded to climate change over time, the researchers resurveyed sites that scientist Joseph Grinnell visited in the early twentieth century. The researchers then compared the century-old data to their modern findings.

Specifically, the scientists used simulation models to predict the likelihood of animal occupation of each site — in both the past and present.

The same simulation model also considered the impacts of the climate crisis, such as changes in precipitation and temperature increase, on the likelihood of animal habitation in the desert.

The scientists also used a heat flux model to predict how exposed or vulnerable small mammals and birds were to heat changes, based on certain behavioral responses.

Sharp-shinned Hawk, a desert animal surveyed in the study.

Credit: Sean Peterson

What's new — The results startled the scientists: Previous studies on heat exposure suggested animals living in similar desert environments would face similar species decline in response to climate change.

But those studies didn't take into account the diverse strategies desert animals might deploy in response to rising temperatures.

"Prior to analyzing the results for small mammals, we had published on the collapse of the desert bird community, so in part, we thought that small mammals might mirror the bird declines," Riddell says.

"However, we also suspected that small mammals might be able to avoid some of the physiological costs that birds faced due to their nocturnal and fossorial [underground] lifestyle."

The study proved this hunch correct. The team found, over time, "small mammal communities remained remarkably stable" while "birds declined markedly in response to warming and drying."

Cactus mouse, a desert animal surveyed in the study.

Credit: Jack Daynes

Small mammals were able to mitigate the effects of rising desert temperatures by hiding out in cooler underground burrows, which the study calls "microhabitats."

This held true even for both nocturnal animals and diurnal animals

"In our study system, we studied small mammals that are active at night, like the desert woodrat, or during the day, such as the white-tailed antelope squirrel," Riddel says. "Even though the squirrels are active during the hottest time of day, they still have immediate access to cool microhabitats underground when temperatures get too hot."

Digging into the details — Birds, however, lacked such protective microhabitats, and, were more affected by climate change — especially when it came to cooling costs.

Cooling costs refers to the amount of water that animals require to stay cool in the desert heat, which the study calls "a critical aspect of survival for desert birds and mammals.

The study reports:

"Cooling costs were higher in birds than in mammals by a factor of 3.3 across arepresentative landscape, and climate change increased these costs by 58.5 percent for birds but only 17.4 percent for mammals."

In fact, the vast majority — 80 percent — of small mammals hardly encountered any change in cooling costs at all.

Ultimately, only 9 percent of mammal species declined at the sites surveyed, compared to 29 percent for the bird species.

Why this matters — Climate change is expected to make desert environments even hotter, and even less hospitable to birds.

Cooling costs are "projected to be greater for birds than for mammals by a factor of 3.8 across a representative Mojave landscape by 2080," the study team writes.

Species already taking advantage of cool microhabitats have an edge when it comes to avoiding the direct effects of climate change, Riddell says.

Ultimately, the researchers were most surprised to find that evolutionary adaptations didn't play as big a role in responding to desert climate change as they anticipated.

Although some desert rodents are better suited for dry climates, these small mammals didn't survive climate change because they were inherently adapted better to rising temperatures than birds — they just had a built-in microhabitat advantage.

Mojave Desert at sunrise

Eric Riddelll

What comes next — In order to understand how we can avoid species collapse in the wake of climate change, we have to first understand the strategies that animals are using to stay alive.

"It's critical to understand whether organisms can avoid the direct effects of climate change by sheltering in cool microhabitats, while still being able to forage, find mates, and do all of the necessary activities to sustain their population," Riddell says.

But, oddly enough, we've also seen something similar happen before: during the age of the dinosaurs.

Or, more precisely: the decline of the dinosaurs. During the mass extinction event that wiped out three-quarters of animal life on Earth, the dinosaurs died, but some smaller mammals survived.

Birds are derived from dinosaurs. In a 2015 experiment, scientists observed chickens with "experimental tails" in an effort to see how dinosaurs may have walked.

"The small mammals of the desert and their prehistoric ancestors share the same ability to avoid rapid environmental change, but it's also important to remember that the majority of mammals perished with the dinosaurs 65 million years ago," Riddell says.

As the descendants of dinosaurs, birds may ultimately share a similar fate to their ancestors — but Riddell says we shouldn't get ahead of ourselves.

"I wouldn't necessarily go that far. The effects that we measured are specific to the Mojave region, and though we are seeing declines in birds in many other places, there are likely many causes underlying their declines outside of the Mojave," Riddell says.

"I think we are seeing the beginning of a different desert ecosystem that will likely continue as climates get warmer," he adds.

Desert ecosystems are certainly forever. It's possible small mammals will survive using a similar tactic employed by their ancient forebears.

"Though human-caused climate change and the climate catastrophe 65 million years ago have some important differences, it's clear that hiding underground is an effective strategy to persevere during extreme environmental change," Riddell says.

Abstract: High exposure to warming from climate change is expected to threaten biodiversity by pushing many species toward extinction. Such exposure is often assessed for all taxa at a location from climate projections, yet species have diverse strategies for buffering against temperature extremes. We compared changes in species occupancy and site-level richness of small mammal and bird communities in protected areas of the Mojave Desert using surveys spanning a century. Small mammal communities remained remarkably stable, whereas birds declined markedly in response to warming and drying. Simulations of heat flux identified different exposure to warming for birds and mammals, which we attribute to microhabitat use. Estimates from climate projections are unlikely to accurately reflect species’ exposure without accounting for the effects of microhabitat buffering on heat flux.

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