Mojave Desert birds have suffered major collapse over the past century, scientists say

Ian James | The Republic | azcentral.com

Show Caption Hide Caption Audubon Arizona is looking for volunteer bird counters to track migration Audubon Arizona is looking for bird counting volunteers to help collect data about birds along the state's western rivers.

In 1908, biologist Joseph Grinnell began leading hundreds of research expeditions throughout California to collect animals as museum specimens and catalog the wildlife in the forests, mountains and deserts.

The meticulous notes he and his colleague took over four decades captured scientific snapshots of the wildlife in the first half of the 20th century, including surveys of birds in many areas of the Mojave Desert.

In the past several years, scientists have used those detailed records to retrace the steps of Grinnell's survey teams at dozens of sites across the Mojave in California and Nevada. And they've come to a striking conclusion: There are far fewer birds in the desert than there used to be.

In a newly published study, researchers from the University of California, Berkeley, say they discovered widespread declines of many species, from American kestrels to olive-sided flycatchers — a massive collapse they attribute to climate change.

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Of the 135 bird species found in the Mojave Desert in the early 20th century, 39 species have become less common.

The researchers surveyed 61 sites in the desert and found that, on average, there were 43 percent fewer species of birds than a century ago.

"We almost have lost half of the species that used to be there," said Steve Beissinger, a professor of conservation biology at UC Berkeley who coauthored the study. "The number of places where you find them has been eroding away and shrinking."

Birds reach limits in drying places

In other parts of the country, bird habitats have been lost to development. But the research focused on relatively undisturbed areas of the desert, including parts of Death Valley and Joshua Tree national parks, as well as Mojave National Preserve in Southern California and protected federal lands in Nevada — places where ecosystems have generally been seen as remaining intact.

"We think about this as a collapse of the whole community of birds. It's not just one or two species," Beissinger said. "And this collapse of the community has been due to the drying and warming caused by climate change. Especially the drying seems to be pushing species over the edge."

Raptors, including prairie falcons, turkey vultures and sharp-shinned hawks, are some of the species that were more common in the early 20th century and have declined dramatically.

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Other birds that have seen major declines include northern mockingbirds, white-throated swifts, western kingbirds, violet-green swallows, common yellowthroats, house sparrows, mountain quail and western meadowlarks, among others.

"It was surprising to be able to record this level of decline," said Kelly Iknayan, a UC Berkeley graduate student who coauthored the study after leading the surveys with a team of researchers. "Deserts are harsh environments, and while some species might have adaptations that allow them to persist in a desert spot, they are also at their physiological limits."

Fewer birds could affect plants

Many of the birds that have become less common, such as mockingbirds, killdeer and various sparrows and flycatchers, are also found in other habitats in addition to the desert. Iknayan said taking steps to protect these bird populations throughout their entire ranges could help them survive.

"California deserts have already experienced quite a bit of drying and warming because of climate change," Iknayan said. "It seems like we are losing part of the desert ecosystem."

Birds that are adapted to the desert, such as the cactus wren and the roadrunner, also declined but fared better than other birds.

Four nonnative species have taken hold in the Mojave over the past century: the Eurasian collared dove and European starling, which were introduced by people; an imported gamebird called the chukar; and the great-tailed grackle, which migrated north from parts of the Southwest and Mexico.

The scientists found only one native bird species that has flourished and expanded in the desert: the common raven. Ravens have also thrived around towns and cities, sometimes feeding on trash.

Iknayan said the overall decline in bird populations could affect desert plants, which rely on birds for pollination and for spreading seeds.

Her team found that although the declines have occurred across the Mojave Desert, birds fared better around oases where springs and water holes nourish plants and wildlife, suggesting that dehydration is a factor driving the trend.

Some of the natural springs that were flowing in Grinnell's time have dried up, Beissinger said, and the causes seem to include a long-term decrease in rainfall in the region as well as groundwater pumping in some areas.

'A wake-up call'

To help prevent more losses of birds, the scientists suggested limiting groundwater pumping and pursuing short-term solutions like establishing more artificial water sources, or "guzzlers," in the desert to sustain wildlife.

In the big picture, they said, their findings point to a need for action to reduce emissions of planet-warming greenhouse gases.

"This has occurred in our national jewels, our national parks. So, it should be a wake-up call for us that we really can no longer think about climate change as business-as-usual," Beissinger said.

"We need to be switching to clean energy in order to slow those trends of carbon emissions into the atmosphere and start to reverse the effects of climate change," he said. "It's a slow process but there can be no more waiting for it to happen, no more wishing."

The study, which was published this week in the journal Proceedings of the National Academy of Sciences, adds to a growing body of research on the threats climate change poses for a wide variety of animals and plants across the United States and around the world.

Scientists calculate that species have been going extinct globally at roughly a thousand times the rate of natural extinction before the development of human civilization, and the losses of species from frogs to fish are projected to accelerate as temperatures climb.

The desert Southwest is one of the regions where scientists say the shift toward a hotter, drier climate has been especially pronounced, and where climate-threatened species include lizards, desert tortoises and iconic Joshua trees.

In their study, the researchers wrote that their results "provide evidence that bird communities in the Mojave Desert are collapsing to a new, lower baseline that supports about half the local species richness that was present a century ago."

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Retracing a landmark survey

Grinnell began his work leading the Museum of Vertebrate Zoology at UC Berkeley in 1908, and over the next four decades he and his colleagues surveyed 61 sites in the Mojave Desert in southeastern California and southern Nevada.

Between 2013 and 2016, researchers revisited those sites as part of the Grinnell Resurvey Project, which Beissinger leads.

Following a set of procedures, Iknayan and her fellow researchers spent three days at each spot counting birds. Her surveys involved walking a path and stopping at 10 places, taking note of all the birds she saw or heard within seven minutes.

She and Beissinger conducted a statistical analysis of the survey results and examined other data for the research sites, including long-term changes in average temperatures and yearly rainfall.

They found that the most significant change linked to declines in bird populations was a long-term decrease in precipitation, and that the long-term increase in high temperatures at a site was unrelated to the loss of species. They also found that birds declined more in places where rainfall decreased more.

The study didn't include parts of the Mojave in northwestern Arizona or the hotter, lower-elevation Sonoran Desert.

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Missing birds in other deserts

David Pearson, a professor at Arizona State University's School of Life Sciences who wasn't involved in the study, said the research methods were appropriate and the findings are "very credible."

"A lot of the species they looked at are these marginal species that are just barely into the desert but occupy other habitats as well," Pearson said. "So, they're not supremely adapted for the desert in the first place, and they're going to also be the most sensitive to any changes."

He pointed out that separating the effects of human-caused climate change from cyclical droughts can be particularly challenging for scientists, but that other studies have found similar changes in the Australian desert and the Kalahari Desert in Africa.

"They're finding very, very similar situations going on in all these deserts around the world," Pearson said. "The Arctic and the desert are places that are very extreme and where we expect to, and are seeing, these changes coming very quickly — that are telling us, as bellwethers, 'watch out.'"

In Arizona, he said, there also are anecdotal signs of shifts in birds, the causes of which are unclear. During the past two years, Pearson said he and other birders have had trouble finding red-faced warblers in the Pinal Mountains and parts of southeastern Arizona.

"They were here, every year, for years and years and years. And all of a sudden, we're not seeing them," Pearson said. "We don't know what's happening. We don't know where they're going."

Andrea Jones, the bird conservation director at Audubon California, said the new research "provides us with an important window into the long-term effects of climate change on bird populations." She said the declines of birds in desert wildlife sanctuaries is particularly troubling.

"Thinking about the silence that one may encounter in those desert areas is hard to comprehend," Jones said in an email. "This is an opportunity to think about both global and local solutions, including local park management to ensure availability for water when birds and other wildlife need it most."

Intense heat takes a toll

Some desert birds may be under added stress due to the extreme heat this summer. Death Valley National Park just had its hottest month on record, with an average temperature of 108.1 degrees in July.

Daytime highs hit 120 degrees or higher many days last month, and on 10 nights, temperatures didn’t drop below 100 degrees.

Park officials found about a dozen dead birds last month, including an owl, a raven and songbirds, with no apparent signs of illness, said Abby Wines, a spokesperson for the national park.

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"We all believe it's due to heat," Wines said. "One thing we're all wondering about is if it's the high overnight lows that might be particularly hard on the birds. When we have overnight lows that are over 100, it's pretty hard for any animal to cool down."

Wines said the latest study — which included bird surveys in Death Valley — provides a rare scientific examination of changes over a much longer period than biologists are capable of seeing during a typical five to 10 years working at the park. She said the findings are valuable and groundbreaking.

"It gives us great information about change that's been happening," Wines said. "However, that leaves us with the challenge of what to do next. How do we handle things differently to help the birds? And we don't have an answer for that."

Ian James writes about water, climate change and the environment for The Arizona Republic. Reach him at ian.james@arizonarepublic.com or @ByIanJames.

Environmental coverage on azcentral.com and in the Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow the azcentral and Arizona Republic environmental reporting team at OurGrandAZ on Facebook, Twitter and Instagram.

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