Birds in southern California’s Mojave Desert are accustomed to living at the extremes. The occasional 120-degree day hardly seems to bother the slowly circling kestrel or broad-chested roadrunners scampering across abandoned highways. But even desert life has its limits: new research suggests that the number of bird species have nearly halved in the Mojave Desert over the last century, and climate change is the likely culprit. The decline in bird species is likely the proverbial canary in the coalmine for the desert’s ecological future – and the desert could be the same warning for other ecosystems.
Scientists from the University of California, Berkeley, resurveyed sites throughout the Mojave Desert that were originally studied at the turn of the 20th century by Joseph Grinnell, a biologist known for his meticulous field research throughout California. The surveys were conducted as part of a larger effort to recreate Grinnell’s research in order to evaluate the ecological changes between his time and ours. Using the same methods that Grinnell and his team employed nearly a century ago, the surveys showed that the 61 sites in the Mojave lost on average 43 percent of their species. The research found that 39 of the 135 breeding bird species studied were less likely to be found at a given site today than 100 years ago.
“It wasn’t what we expected,” says Kelly Iknayan, a PhD student at the University of California, Berkeley, and the lead author of the study. According to Iknayan, similar avian surveys that were conducted in the Sierra Nevada and Central Valley yielded “a little bit more balance” -- only a slight increase in the number of species in the Sierras, and a slight decrease in the Central Valley. In comparison, the changes in the Mojave were dramatic. “When we see a decline across a community like this, it also could potentially indicate that other things are out of balance.”
What's out of balance is rainfall. Climate change has altered precipitation patterns in the desert, leading to the survey sites receiving 20 percent less precipitation than when they were first studied. Precipitation impacts the amount of surface water available and the health of the plants birds use for sustenance and hydration. The researchers determined that this decline in rain and snow was the major cause for the shriveling bird populations, not rising temperatures (which have not yet increased to the point of dehydrating birds more rapidly) or increased wildfires caused by flammable invasive species.
Desert birds seek refuge in areas with higher elevation, more surface water, and higher levels of precipitation. But over time as precipitation continues to decline, these refuges are also drying up. Birds are more likely to suffer from lethal dehydration before they can escape to the refuges or move out of the desert Southwest all together.
The research also observes that there are no new species replacing the lost birds in the Mojave Desert.
“What we found in the Mojave that it was a lot of decline without any really climatological winners across bird species,” says Iknayan. “It may mean that these sites are becoming too inhospitable for new species to be coming in and colonizing.”
There was one notable exception: the common raven, which showed increased populations across the sites. Across North America, the scavengers have proliferated as new sources of once-limited food and water resources become available in the form of human-made landfills, roadkill, Dumpsters, sewage ponds and golf courses. In the Mojave Desert, increased raven populations threaten other native species like the desert tortoise. In this case, the raven’s persistence is a red herring rather than good news, serving as yet another example of the impacts human activity can have on the desert ecosystem.
“The ravens are incredibly adaptable,” says Andrea Jones, director of bird conservation at Audubon California. “They’re a desert bird, but they have also spread across other parts of coastal California. They are highly mobile and survive well because they’re opportunistic feeders.”
According to Jones, birds are useful indicators of an ecosystem’s health because they are diverse, deeply connected to their habitats, highly mobile, and generally conspicuous. Recorded observations from bird enthusiasts have also made birds a popular proxy for ecological change, though the Mojave Desert is a notable exception. “You can go through a vast stretch of the desert and not see many birds, and then find a green patch,” Jones says.
Despite their elusiveness, the diversity of birds serve many functional roles in the Mojave ecosystem. Costa’s hummingbirds are important pollinators, golden eagles are apex predators, and vultures are scavengers. Phainopepla – which Jones describes as the “quintessential bird of the Mojave desert” – is essential for dispersing seeds in an ecosystem where patches of life exist like islands in large swaths of unforgiving open desert. The Mojave’s habitability for avian species is also important for migrating birds needing rest stops as they fly across the desert to reach their breeding grounds. If bird populations continue to drop, the impacts would likely cascade throughout the desert ecosystem.
The changes in the desert may also portend a less bird-friendly future for other ecosystems. Over the past century, deserts around the world have warmed and dried more rapidly than other areas. Though the declines in bird population observed other regions of California could not compare with those in the Mojave, Steve Beissinger, senior author on the research, explains that the impacts of climate change are nuanced for different ecosystems. “Climate change is kind of lumpy,” he explains. “It’s happening at different rates in different places.” Beissinger says it is hard to predict whether similar bird surveys in other ecosystems will show dramatic declines in the near future, the changes in the desert likely forebode broader climactic trends over time.
“The deserts are in trouble,” Beissinger warns, “and outside of the Arctic, they’re probably the next hot spot for climate change.”
One of the research’s most troubling findings was that even national parks and protected lands were not immune to the avian collapse. Land use in the Mojave Desert overall has not changed much since Grinnell’s original surveys; about 85 percent of land studied was undisturbed and ecologically intact, which removed complicating land-use change variables like increased grazing. Even so, some of the greatest declines were observed in Death Valley, the largest national park in the lower 48 states, where 90 percent of the land is designated wilderness.
“It’s a shot across our bow; it’s a warning,” says Beissinger. “It's pretty clear to us that despite the fact that we’ve protected these lands, we’re going to have trouble keeping all the species that are part of those [desert] ecosystems.”
The desert’s lands face even more pressures now than in Grinnell’s time. Extractive groundwater projects could threaten desert springs and impinge on birds’ already limited water. The desert is also often caught in a climatic catch-22 as renewable energy companies look to raze desert habitat for large-scale infrastructure. Solar farms have been particularly eager to develop in the Mojave Desert, where large swaths of land in full sunlight are plentiful, but existing solar farms have been documented to be lethal to birds.
“We are really in need of having renewable development to curb greenhouse gases, but we can continue to do so in ways that are not using area that are critical habitat,” Iknayan says. “We as humanity need to evaluate how we interface with the natural world."
Editor's note 8/9/18: We've corrected a quote from Audubon California's Andrea Jones to clarify where ravens are spreading. They're moving to coastal California, not northern California.